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U.S. Department of Health and Human Services

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NADA 141-079 Ivomec® Eprinex™ Pour-On - original approval (continued 3)

d. Results:

 

 

Table V.A.2. Results of cow breeding and calving data (ASR 13639).
VariableGroup 1
Control
Group 2
Before Mating
Group 3
During Mating
Group 4
After Mating
Cows32323232
Brangus16161616
Hereford16161616
Cows pregnant2930a2628
Brangus1414a13b13
Hereford15b161315b
Cows calvingc29292628
Brangus14151313
Hereford1515c1315d
Perinatal Deathsd0123
Brangus0110
Hereford0013
Assisted births1014
Brangus0000
Hereford1014
Calves alive at 30 days29292524e
Brangus14141313
Hereford15151211
a One cow was dropped from the study when it was discovered she was pregnant at the time of study initiation.
b Does not include 1 cow that was initially diagnosed pregnant, but determined to be open at a later date.
c One cow aborted
d Includes one still birth
e One calf died 6 days after birth and is not included in perinatal deaths (see text).

 

 

Table V.A.3. Calf average daily gains and birth weights (ASR 13639).
VariableControlTreatment
before mating
Treatment
during mating
Treatment
after mating
Calf birth weight32.132.732.431.8
Brangus29.829.929.228.6
Hereford34.335.535.634.9
Calf avg. daily gain- birth to 30 days1.071.151.131.08
Brangus1.141.211.131.11
Hereford1.001.091.121.05

There were no significant (p>0.10) differences between the control group and any of the eprinomectin-treated groups for cow average daily weight gain from allocation to calving, from calving to 30 days after calving, or from allocation to final weighing, or for birth weight or calf average daily gain from birth to final weighing.

There were no significant (p>0.10) differences between the control group and any of the eprinomectin-treated groups for number of cows pregnant, number calving, perinatal deaths and assisted births. There was a significant (0.1>p>0.05) difference between the control group and the group treated with eprinomectin after mating (Group 4) for the number of calves alive at the final examination (30 day examination).

There were seven calf deaths, six of which occurred during parturition or on the day of birth. Four of these six calves, three from Group 4 and one from Group 3, resulted from assisted calvings. Two of the calves were abnormally presented at parturition and in the other two, the investigator noted that the cows had a narrow pelvic canal. No abnormalities were found in the calves except those attributable to parturition trauma and/or anoxia. The fifth calf (Group 2), weighed only 18.5 kg at birth and died without nursing. The sixth calf (Group 3), was one of twins. Its forelegs were not fully extended and it died within 8 hours of birth. The other twin survived to trial termination. The seventh calf (Group 4), died 6 days after birth from an eviscerated umbilical hernia. The calf had no abnormalities reported when examined soon after birth and the herniation with subsequent evisceration was presumed to have resulted from trauma.

e. Statistical Analysis: For the dichotomous variables (i.e., pregnant vs non-pregnant), the control group was compared to each eprinomectin-treated group. The comparisons were made using Fisher's Exact Test. All cows were included for the analysis of number of cows pregnant. Only pregnant cows were used in the subsequent analyses: number calving, perinatal deaths, assisted births and calves alive at the final examination.

The continuous variables (weight and average daily gain) were analyzed using analysis of variance for a mixed-model design, with the factors of breed, paddock within breed, replicate within breed and paddock, treatment, and interactions of treatment with breed and treatment with paddock within breed. Single degree of freedom contrasts were done comparing the controls to each eprinomectin-treated group.

f. Conclusions: Eprinomectin administered topically at 3X the recommended therapeutic dose had no attributable adverse effect on cows at all stages of breeding and pregnancy or on their calves.

B. Overall Conclusions

The following paragraph summarizes the Target Animal Safety studies and is found on the label under the ANIMAL SAFETY section.

The safety of eprinomectin was tested in cattle 8 weeks of age and older. Tolerance and toxicity studies have demonstrated the margin of safety for eprinomectin in cattle. In the toxicity study, 8-week-old calves showed no adverse effects after treatment with eprinomectin administered at up to 5 times the recommended dose three times at 7 day intervals. In the tolerance study, one of 6 cattle treated once at 10 times the recommended dose showed clinical signs of mydriasis. Application of three times the recommended dose had no adverse effects on the breeding performance of cows or bulls.

 

VI. HUMAN SAFETY

A. Toxicity Tests

1. Microbial Mutagen Tests With and Without Rat Liver Enzyme (S-9) Activation

a. Report Number: TT #90-8004.

b. Study Dates: Started 16JAN90, ended 18JAN90.

c. Principal Investigators: J. Sina and M. Kloss.

d. Laboratory: Merck Research Laboratories, West Point, PA.

e. Substance and Dosage Form Tested: MK-0397 (L-653,648) as a solution in DMSO. Positive control mutagens were used as follows: 2-aminoanthracene (2-10 µg/plate with and without metabolic activation with all Salmonella strains and Escherichia coli strains WP2 uvrA and WP2 uvrA pKM101 and hydrazine sulfate (500 and 1000 µg/plate) with metabolic activation for E coli strain WP2.

f. Species and Strain: Salmonella typhimurium (TA1535, TA97a, TA98, and TA100) with and without rat liver S-9 microsomal activation system. Escherichia coli (WP2, WP2 uvrA, WP2 uvrA pKM101).

g. Dose Levels Tested: 100, 300, 1000, 3000, and 10,000 µg/plate. Positive control mutagens with S-9 and without S-9 gave the expected response.

h. Results: No two-fold increases in revertants, relative to the vehicle controls in any of the tester strains.

2. In Vitro Alkaline Elution/Rat Hepatocyte Assay

2.1 First Assay:

a. Report Number: TT #90-8305.

b. Study Dates: Started 10JAN90, ended 10JAN90.

c. Principal Investigators: R. Storer and M. Kloss

d. Laboratory: Merck Research Laboratories, West Point, PA.

e. Substance and Dosage Form Tested: MK-0397 (L-653,648-000X012) as a solution in DMSO.

f. Species and Strain: Crl:CD®(SD) BR rat hepatocytes.

g. Dosage Levels Tested: 3, 10, 30, 100, 300, and 500 uM

h. Results: Relative viability ranged from 105 to 30 percent of controls over the dose range of 3 to 500 µM. Concentrations of 100 µM and above resulted in excessive cytotoxicity for assessment of DNA damage in subsequent studies in the alkaline elution/rat hepatocyte assay.

2.2 Second Assay:

a. Report Number: TT #90-8309.

b. Study Dates: Started 13FEB90, ended 15FEB90.

c. Principal Investigators: R. Storer and M. Kloss

d. Laboratory: Merck Research Laboratories, West Point, PA.

e. Substance and Dosage Form Tested: MK-0397 (L-653,648-000X012) as a solution in DMSO.

f. Species and Strain: Crl:CD® (SD)BR rat hepatocytes.

g. Dosage Levels Tested: 10, 15, 23, 34, and 51 µM. Aflatoxin B1 at a concentration of 1 µM was used as the positive control.

h. Results: MK-0397 did not give an induced elution slope of 0.034 or greater (criteria for a positive response) at any non-cytotoxic concentration. The positive control produced an induced elution slope of 0.087 with 98% relative cell viability. Therefore, MK-0397 is considered negative in this assay.

2.3 Third Assay:

a. Report Number: TT #90-8314.

b. Study Dates: Started 28FEB90, ended 02MAR90.

c. Principal Investigators: R. Storer and M. Kloss

d. Laboratory: Merck Research Laboratories, West Point, PA.

e. Substance and Dosage Form Tested: MK-0397 (L-653,648-000X012) as a solution in DMSO.

f. Species and Strain: Crl:CD® (SD)BR rat hepatocytes.

g. Dosage Levels Tested: 10, 15, 22, 29, and 35 µM. Aflatoxin B1 at a concentration of 1 µM was used as the positive control.

h. Results: MK-0397 did not give an induced elution slope of 0.034 or greater (criteria for a positive response) at any non-cytotoxic concentration. The positive control produced an induced elution slope of 0.087 with 98% relative cell viability. Therefore, MK-0397 is considered negative in this assay.

3. In Vitro V-79 Mammalian Cell Mutagenesis Assay With and Without Rat Liver Enzyme (S-9) Activation

3.1 First Assay:

a. Report Number: TT #91-8502.

b. Study Dates: Started 26APR91, ended 02MAY91.

c. Principal Investigators: J. DeLuca and M. Kloss

d. Laboratory: Merck Research Laboratories, West Point, PA

e. Substance and Dosage Form Tested: MK-0397 (L-653,648-000X014) as a solution in DMSO.

f. Species and Strain: V-79 Chinese hamster lung cell line.

g. Dosage Levels Tested: 10, 20, 30, 40, 50, 60, 70, and 80 µM with and without rat liver S-9 metabolic activation.

h. Results: Plating efficiency ranged from 79 to 14 percent of controls over a dose range of 10 to 40 µM with S-9 and from 43 to 11 percent over the same dose range without S-9. At concentrations above 40 µM relative plating efficiency was <0.3 percent.
3.2 Second Assay:

a. Report Number: TT #91-8510.

b. Study Dates: started 10MAY91, ended 17MAY91.

c. Principal Investigators: J. DeLuca and M. Kloss

d. Laboratory: Merck Research Laboratories, West Point, PA.

e. Substance and Dosage Form Tested: MK-0397 (L-653,648-000X014) as a solution in DMSO.

f. Species and Strain: V-79 Chinese hamster lung cell line.

g. Dosage Levels Tested: 5, 10, 30, and 40 µM with S-9 and 1, 3, 7, 10, 30, and 40 µM without rat liver S-9 metabolic activation.

h. Results: Plating efficiency ranged from 95 to 18 percent of controls over a dose range of 5 to 40 µM with S-9 and from 80 to 12 percent over a dose range of 1 to 40 µM without S-9.

3.3 Third Assay:

a. Report Number: TT #91-8503.

b. Study Dates: Started 04JUN91, ended 27JUN91.

c. Principal Investigators: J. Deluca and M. Kloss.

d. Laboratory: Merck Research Laboratories, West Point, PA.

e. Substance and Dosage Form Tested: MK-0397 (L-653,648-000X014) as solution in DMSO.

f. Species and Strain: V-79 Chinese hamster lung cell line.

g. Dosage Levels Tested: 0.01, 0.02, 0.03, and 0.04 µM with S-9 metabolic activation and 0.001, 0.005, 0.02, and 0.04 µM without S-9. Positive controls used were methylnitrosourea without S-9 and 3-methylcholanthrene with S-9.
h. Results: Statistical analyses of the mutation frequencies with MK-0397 with and without S-9 did not result in any significant increases relative to the solvent controls. All mutation frequencies with MK-0397 were within the laboratory's 95% confidence limit for historical controls. The positive control mutagens resulted in highly significant increases in mutation frequency (P < 0.001) compared to the solvent control. Therefore, MK- 0397 is considered negative for induction of mutations in V-79 mammalian cells in vitro.

4. In Vitro Assay for Chromosomal Aberrations With and Without Rat Liver Enzyme Activation (S-9) in Chinese Hamster Ovary Cells

4.1 First Assay:

a. Report Number: TT #90-8611.

b. Study Dates: Started 06FEB90, ended 07FEB90.

c. Principal Investigators: S. Galloway and M. Kloss

d. Laboratory: Merck Research Laboratories, West Point, PA

e. Substance and Dosage Form Tested: MK-0397 (L-653,648-000X012) as a solution in DMSO. Cyclophosphamide at a concentration of 5 µM with S-9 and mitomycin C at a concentration of 0.5 µM without S-9 were used as positive controls.

f. Species and Strain: Chinese hamster ovary (CHO) cells, Clone WBL.

g. Dosage Levels Tested: 0.08, 0.16, 0.31, 0.63, 1.3, 2.5, 5.0, 10.0 and 20.0 µM with and without S-9 metabolic activation.

h. Results: Cell counts 85 to 1 percent of negative controls were found at 5 and 10 µM with S-9 with no significant effect on cell survival at concentrations < or = 2.5 µM. Without S-9 cell counts ranged from 76 to 13 percent of negative controls at concentrations of 10 and 20 µM. No effects on survival were found at concentrations < or = 5.0 µM without S-9. The positive controls, cyclophosphamide and mitomycin C, produced cell counts of 68 and 75 percent of the negative controls, respectively, as expected.

4.2 Second Assay

a. Report Number: TT #90-8614.

b. Study Dates: Started 13MAR90, ended 30APR90.

c. Principal Investigators: S. Galloway and M. Kloss.

d. Laboratory: Merck Research Laboratories, West Point, PA.

e. Substance and Dosage Form Tested: MK-0397 (L-653,648-000X012) as a solution in DMSO.

f. Species and Strain: Chinese hamster ovary (CHO) cells, Clone WBL.

g. Dosage Levels Tested: 5, 6, and 7 µM with S-9 and 8, 10, and 12 µM without S-9 activation. Mitomycin C at concentrations of 0.25, 0.35, 0.5, and 0.75 µM without S-9 and Cyclophosphamide at 2.5 and 5.0 µM with S-9 were included as positive controls.

h. Results: Cytotoxicity of 63% cell survival was produced at concentrations of 12 µM without S-9 with 68% survival at a concentration of 7 µM with S-9. No significant increases in percentages of cells with chromosome aberrations were found in the treated groups relative to the solvent or untreated controls. The positive control mutagens produced statistically significant increases (P < 0.05) in the number of cells with aberrations relative to the solvent control. Therefore, MK-0397 is considered negative for production of chromosomal aberrations in vitro in CHO cells.

5. In Vivo Assay for Micronucleus Induction in Mouse Bone Marrow

a. Report Number: TT #93-8719.

b. Study Dates: started 07DEC93, ended 18APR94.

c. Principal Investigators: S. Galloway and M. Kloss.

d. Laboratory: Merck Research Laboratories, West Point, PA.

e. Substance and Dosage Form Tested: MK-0397 (L-653,648-000X021) as a suspension in 0.5% aqueous methylcellulose administered at a dose volume of 0.1 ml/10 g body weight.

f. Species and Strain: Mouse, Crl:CD-1®(ICR)BR strain.
g. Dosage Levels Tested: 0, 10, 20, and 40 mg/kg administered to 10 mice/sex/group. The negative control received the vehicle only while the positive controls (5 mice/sex) received 0.35 and 2.0 mg/kg of Mitomycin C. Five mice/sex/group were sacrificed at 24 and 48 hours after dosing for harvesting bone marrow for examination except for the positive control groups which were sacrificed only at 24 hours after Mitomycin C treatment. Approximately 2000 cells per animal were examined.

h. Results: Clinical signs of toxicity including ptosis, decreased activity, bradypnea, ataxia, tremors, and spastic movements were observed within 4 hours after dosing with MK-0397 in all animals at 40 mg/kg. Most animals were normal by 24 hours after treatment. Similar signs were observed in 2 of 10 males treated with 20 mg/kg of MK-0397. All animals survived until scheduled necropsy. No dose group treated with MK-0397 at either sacrifice time had a significant (P < or = 0.05) increase in micronucleated polychromatophilic erythrocytes compared to the concurrent control by pairwise comparison. There were highly significant increases (P < 0.001) in micronucleated polychromatophilic erythrocytes in the positive control groups. Therefore, MK-0397 is negative for induction of micronucleated polychromatophilic erythrocytes in mouse bone marrow in vivo.

6. Fourteen-Week Oral Toxicity Study in Rats

a. Report Number: TT #90-037-0.

b. Study Dates: Started 28MAR90, ended 28JUN90 (Males) and started 30MAR90, ended 29JUN90 (Females).

c. Principal Investigators: H. Allen, J. Coleman, and M. Kloss.

d. Laboratory: Merck Research Laboratories, West Point, PA.

e. Substance and Dosage Form Tested: MK-0397 (L-653,648-000X012).

f. Species and Strain: Rat/Sprague-Dawley (Crl:CD®(SD)BR).

g. Number of Animals/Sex/Group: 20 rats/sex/group.

h. Dosage Levels Tested: 0, 1, 5, and 30/20 mg/kg/day.

i. Route of Administration: Oral via diet.

j. Parameters Examined: Physical signs daily, body weights and food consumption weekly, ophthalmic exams on all control and high dose group animals in weeks 4, 7, and 12 for males and 3, 7, and 12 for females, hematology and serum biochemistry in weeks 4, 8, and 12, urinalysis in weeks 8 and 12 on all animals. Complete necropsies and organ weights recorded for all animals. Histology conducted on all control and high dose group animals and gross lesions and target organs examined for all animals in all groups.

k. Toxicity Observed: Whole body tremors and decreased food consumption and body weight gain were found in the high dose group males and females, necessitating lowering the high dose level from 30 to 20 mg/kg/day in week 4 (females) and week 5 (males). The high dose females had decreased lymphocyte counts relative to controls throughout the study while both sexes in the high dose group had slight elevations in blood urea nitrogen and increased urinary specific gravity. Also, there was evidence of hemoconcentration in the high dose group based on increases in the erythron and serum protein concentrations. Postmortem examination revealed a variety of organ weight changes which were statistically significant (P < or = 0.05) compared to controls in the high dose group only. Treatment-related histologic changes were limited to sciatic nerve degeneration in the high dose group only.

l. No-Observed-Effect Level: 5 mg/kg/day.

7. Fifty-Three-Week Oral Toxicity Study in Dogs

a. Report Number: TT #92-116-0.

b. Study Dates: Started 10DEC92, ended 17DEC93.

c. Principal Investigators: W. Bagdon, L. Gordon, and M. Kloss

d. Laboratory: Merck Research Laboratories, West Point, PA.

e. Substance and Dosage Form Tested: MK-0397 (L-653,648-000X021) as a suspension in 0.5% aqueous methylcellulose administered at a dose volume of 5 ml/kg body weight.

f. Species and Strain: Dogs, Beagle.

g. Number of Animals/Sex/Group: 4/sex/group.

h. Dosage Levels Tested: 0, 0.5, 1.0, and 2.0 mg/kg/day.

i. Route of Administration: Oral via gavage.

j. Parameters Examined: Physical signs daily, body weights weekly, food consumption daily 2-5 times each week, ophthalmic exams pretest and in weeks 13, 28, 39, and 53, hematology and serum biochemistry in weeks 4, 12, 25, 39, and 51, urinalysis in weeks 12, 25, 39, and 51 for all dogs. Electrocardiograms were recorded pretest and in weeks 12, 26, 38, and 52 for all dogs. Complete necropsies and organ weights were recorded for all animals. Histology was conducted on all control and high dose group animals and gross lesions and target organs examined for all animals in all groups.

k. Toxicity Observed: Mydriasis was observed in the high dosage group dogs throughout the study. In addition, one high dose group animal became progressively less active, with salivation, weight loss, ataxia and recumbency. This animal was sacrificed in week 13. There were no treatment-related postmortem findings in this animal. Treatment-related postmortem findings were limited to very slight focal neuronal degeneration in the cerebellum in 3 of 8 high dose group dogs.

l. No-Observed-Effect Level: 1.0 mg/kg/day.

8. Oral Developmental Toxicity Study in Rats

a. Report Number: TT #90-718-0.

b. Study Dates: Started 09JUL90, ended 03AUG90.

c. Principal Investigators: M. Cukierski and M. Kloss.

d. Laboratory: Merck Research Laboratories, West Point, PA

e. Substance and Dosage Form Tested: MK-0397 (L-653,648-000X014) as a suspension in 0.5% aqueous methylcellulose at a dose volume of 5 ml/kg body weight.

f. Species and Strain: Rat/Sprague-Dawley (Crl:CD[[dieresis]](SD)BR).

g. Number of Animals/Sex/Group: 25 females/group.

h. Dosage Levels Tested: 0, 0.5, 1.0, 3.0, and 12.0 mg/kg/day administered on gestation days 6-17.

i. Route of Administration: Oral via gavage on days 6 through 17 of gestation.

j. Parameters Examined: Physical signs daily, food consumption measured over three-day interval from days 3-20 of gestation, maternal body weights recorded on days 0, 6, 8, 10, 12, 14, 16, 18, and 20 of gestation. Reproductive parameters examined included the numbers of corpora lutea, implants, resorptions, live and dead fetuses, fetal weights, and external, visceral, and skeletal examination of fetuses. In addition, a gross necropsy was performed on all sacrificed dams.

k. Toxicity Observed: During the treatment period, increased body weight gains were found in the 3 and 12 mg/kg/day groups. However, following treatment on gestation days 18 to 20, there were significant (P < or = 0.05) treatment-related decreases in body weight gain in the 3 and 12 mg/kg/day groups compared to controls. Treatment-related increases in food consumption paralleled the increased body weight gains during the treatment period in these same groups. There was no evidence of developmental toxicity in any of the treated groups based on postimplantation survival, fetal weights, or external, visceral, or skeletal fetal examinations.

l. No-Observed-Effect Level: 1.0 mg/kg/day for maternal toxicity and > 12 mg/kg/day (highest dose tested) for developmental toxicity.

9. Oral Developmental Toxicity Study in Rabbits

a. Report Number: TT #90-719-0.

b. Study Dates: Started 02OCT90, ended 02NOV90.

c. Principal Investigators: L. D. Wise and M. Kloss.

d. Laboratory: Merck Research Laboratories, West Point, PA

e. Substance and Dosage Form Tested: MK-0397 (L 653,648-000X014) as a suspension in 0.5% aqueous methylcellulose.

f. Species and Strain: Rabbits, New Zealand White.

g. Number of Animals/Sex/Group: 18 females/group.

h. Dosage Levels Tested: 0, 0.5, 2.0, and 8.0 mg/kg/day.

i. Route of Administration: Oral via gavage on gestation days 6-18.

j. Parameters Examined: Physical signs and food consumption daily, maternal body weights, numbers of corpora lutea, implants, resorptions, live and dead fetuses, fetal weights, and external, visceral, and skeletal examination of fetuses.

k. Toxicity Observed: Slowed pupillary reflex was observed in dams in the 2 and 8 mg/kg/day groups. Slight decreases in maternal body weight gain of about 10% compared to controls were found in the high dose group only. There were statistically significant (P < or = 0.05) decreases in the numbers of implants/pregnant female and live fetuses/pregnant female in the high dose group only compared to controls. Although not statistically significant (P > 0.05) in the mid dose group, these parameters were also decreased relative to controls in this group as well. No other evidence of developmental toxicity was found in this study.

l. No-Observed-Effect Level: 0.5 mg/kg/day for both maternal and developmental toxicity.

10. Oral Embryo/Fetal Viability Study in Rabbits

a. Report Number: TT #94-707-0.

b. Study Dates: Started 21JAN94, ended 23 MAY94.

c. Principal Investigators: M. Cukierski and M. Kloss.

d. Laboratory: Merck Research Laboratories, West Point, PA

e. Substance and Dosage Form Tested: MK-0397 (L 653,648-000X021) as a suspension in 0.5% aqueous methylcellulose.

f. Species and Strain: Rabbits, New Zealand White.

g. Number of Animals/Sex/Group: 24 females/group.

h. Dosage Levels Tested: 0, 1.2, 2.0, and 8.0 mg/kg/day.

i. Route of Administration: Oral via gavage.

j. Parameters Examined: Physical signs daily, maternal body weights, numbers of corpora lutea, implants, resorptions, and live and dead fetuses.

k. Toxicity Observed: Maternal toxicity was limited to the 8 mg/kg/day group and consisted of slowed pupillary reflex and decreased body weight gain during days 6-18 of gestation. There were no effects on preimplantation loss, corpora lutea/pregnant female, implants/pregnant female, percent resorptions plus dead fetuses/implant, or live fetuses per pregnant female.

l. No-Observed-Effect Level: 2 mg/kg/day for maternal toxicity and > 8 mg/kg/day for embryo/fetal viability.

11. Multigeneration Study in Rats

a. Report Number: TT #90-9010.

b. Study Dates: Started 22JUN90, ended 20JUN91.

c. Principal Investigators: A. Brooker, D. Myers, C. Parker.

d. Laboratory: Huntingdon Research Centre Ltd., Huntingdon, Cambridgeshire, England.

e. Substance and Dosage Form Tested: MK-0397 (L-653,648-000X014)

f. Species and Strain: Rat/Sprague-Dawley (Crl:CD"(SD)BR).

g. Number of Animals/Sex/Group: 32/sex/group for F0 generation; 28/sex/group and 24/sex/group for F1 and F2 generations, respectively.

h. Dosage Levels Tested: 0, 6, 18, and 54 ppm (equivalent to approximately 0.5, 1.5, and 4.5 mg/kg/day).

i. Route of Administration: Oral via diet.

j. Parameters Examined: Physical signs, food consumption and body weights were recorded weekly. Water consumption was measured daily over the initial and final two weeks of pre-mating for each generation. Reproductive parameters assessed included mating performance, fertility index, numbers of pups/litter, pup weights and sexual maturation of pups. Histologic examination of the reproductive tract was conducted for the F0 and F1 high dose and control group males and females and target organs and gross lesions from all animals.

k. Toxicity Observed: Increases in body weight gain and food and water consumption were found in the high dose group F0 animals. Decreased mating performance was also evident in the high dose group. Neonatal toxicity characterized by increased pup mortality, tremors, and decreased pup weights were found in the high dose F1 and F2 pups, while toxicity in the mid dose F1 pups was limited to tremors in a few pups. Due to marked increases in food consumption during lactation resulting in increases in drug intake in the F0 and F1 animals, the F1 animals were re-mated and the diet concentrations of drug reduced by a factor of 2 to maintain more constant drug intake values. As a result, drug intake values were approximately 0.4, 1.3, and 3.3 mg/kg/day during lactation of the F2b offspring, compared to values of 1.0, 3.0, and 6.5 mg/kg/day for the F2a offspring. In the F2b offspring tremors were again noted in the high dose group pups. However, no toxicity was found in the mid and low dose group pups

l. No-Observed-Effect Level: 1.0 to 1.5 mg/kg/day.

B. Safe Concentrations of Total Residues

The most appropriate toxicity study for determining the safe concentrations for eprinomectin-related residues in milk and edible tissues is the 53-week oral toxicity study in dogs. The no-observed-effect level (NOEL) for this study is 1.0 mg/kg/day. The Acceptable Daily Intake (ADI) based on a NOEL of 1.0 mg/kg/day and a safety factor of 100 is 10 mcg/kg/day, calculated as follows:

 

 

ADI  =  1.0 mg/kg/day  ÷  100 safety factor  =  10 mcg/kg/day
        (600 mcg/day/60 kg person)

The portion of the ADI set aside for milk is 4%. Consequently, the ADI for cattle is allocated in the following manner:

 

 

ADI (milk)  =   0.4 mcg/kg/day (24 mcg/day/60 kg person)

ADI (tissues)   =   9.6 mcg/kg/day (576 mcg/day/60 kg person)

Safe Concentrations (SC's) for Cattle Tissues and Milk:

 

 

SC (milk)       =   0.4 mcg/kg x 60 kg/1.5L
                =   16 mcg/L or 16 ppb
                
SC (muscle)     =   9.6 mcg/kg x 60 kg/0.3 kg
                =   1920 mcg/kg = 1920 ppb or 1.92 ppm
                
SC (liver)      =   9.6 mcg/kg x 60 kg/0.1 kg
                =   5760 mcg/kg = 5760 ppb or 5.76 ppm
                
SC (kidney)     =   9.6 mcg/kg x 60 kg/0.05 kg
                =   11,520 mcg/kg = 11,520 ppb or 11.52 ppm
                
SC (fat)        =   9.6 mcg/kg x 60 kg/0.05 kg
                    11,520 mcg/kg = 11,520 ppb or 11.52 ppm

C. Total Residue Depletion and Metabolism Studies 1. Total Residue Depletion in Milk.

1.1 Stability of Tritium Labeled L-653,648 in Lactating Dairy Cows Treated Topically with a Single Dose of L-653,648 Labeled with Tritium and Carbon-14 (CA-365).

a. Name and Address of Investigator:

 

 

Narayana I. Narasimhan
Merck Research Laboratories
Box 2000
Rahway, NJ 07065

b. Test Animals: Four lactating Holstein dairy cows in the second lactation and in either the first or the third trimester of milk production were treated in this study.

c. Route of Drug Administration and Time and Duration of Dosing: Test animals were administered a single dose of eprinomectin (L-653,648; MK-0397) topically at 750 mcg/kg body weight (1.5 x the use level).

d. Radiotracers: Two cows were dosed with a dosing solution containing 5-3H-L-653,648 and 14C-N-acetyl-L-653,648. The other two cows were dosed with a second dosing solution containing 4a-methyl-3H-L-653,648 and 14C-N-acetyl-L-653,648. The radiochemical purity of L-653,648 (both tritium and C-14 labels) was in the range of 98.8-99.2% by high performance liquid chromatography. The two dosing solutions used in this study were the same as the formulation to be marketed for use on cattle.

e. Milk Sample Collection: Milk samples were collected at twelve hours predosing, immediately prior to dosing and every twelve hours thereafter until 21 days post-dose.

1.2 Milk, Plasma, and Tissue Radioresidues in Lactating Dairy Cows Treated Topically with a Single Dose of Radiolabeled L-653,648 (Trial CA-367).

a. Name and Address of Investigator:

 

 

Narayana I. Narasimhan
Merck Research Laboratories
P. O. Box 2000
Rahway, NJ 07065

b. Test Animals: Four lactating Holstein dairy cows in either the third or the fourth lactation cycle and in either the first or the third trimester of milk production were treated in this study.

c. Route of Drug Administration and Time and Duration of Dosing: Test animals were administered a single dose of eprinomectin topically at 750 mcg/kg body weight (1.5 x the use level).

d. Radiotracer: Four cows were dosed with a dosing solution containing 5-3H-L-653,648. The radiochemical purity of the drug substance was 99.1% by high performance liquid chromatography. The topical solution used in this study was the same as the formulation to be marketed for use on cattle.

e. Milk Sample Collection: Milk samples were collected at twelve hours predosing, immediately prior to dosing and every twelve hours thereafter until 21 days post-dose.

1.3 Depletion of Total Eprinomectin-Related Residues from Milk.

The milk samples collected during the course of both studies CA-365 and CA-367 were assayed for total radioresidues directly using a liquid scintillation counter. Peak levels of total radioresidues ranged from 3.08 to 25.84 ng/mL (ppb) and occurred during the period of 1.5 - 8.0 days post-dose. Since the total radioresidue levels included the contribution from tritiated water, a by-product of a low level of tritium label loss, the tritiated water levels were subtracted from the total radioresidue levels. The corrected eprinomectin-related peak residue levels were in the range of 2.53 - 24.68 ng/mL.

Since milk is pooled in the dairy industry before being marketed, daily averages of the total residue levels were computed in order to simulate the drug residue levels in the marketed milk. The pooled daily average of the total radioresidues (eprinomectin and structurally related metabolites) peaked at 7.02 ng/mL at 3.0 days post-dose

From the results of studies CA-365 and CA-367, where eight lactating dairy cows were treated topically with eprinomectin at a level of approximately 1.5 times the market dose, all daily averages of the total eprinomectin-related residues in milk samples were below the milk safe concentration of 16 ng/mL.

2. Total Residue Levels in Tissues.

2.1 Depletion of Radioresidues in Tissues of Cattle Dosed Topically with a Single Dose of Radiolabeled MK-0397 (Trial CA-368).

a. Name and Address of Investigator:

 

 

Narayana I. Narasimhan
Merck Research Laboratories
P.O. Box 2000
Rahway, NJ 07065

b. Test Animals: Six heifers and six steers, consisting of Angus and Hereford breeds and eight to ten months of age, were dosed in this study. The twelve cattle were divided into four treatment groups with three animals in each group.

c. Route of Drug Administration and Time and Duration of Dosing: Test animals were administered a single dose of eprinomectin topically at 500 mcg/kg body weight. The animals were sacrificed by groups at 7, 14, 21 and 28 days after dose administration.

d. Radiotracer: The cattle were dosed with a dosing solution containing 5-3H-MK-0397. The radiochemical purity of the drug substance was greater than 98% by high performance liquid chromatography. The topical solution used in this study was the same as the formulation to be marketed for use on cattle.

e. Total Residue Concentration: The following tissues were collected in this study: liver, kidney, fat, dose-site muscle, and muscle. Tissue samples were combusted and subjected to radioactivity analysis in a liquid scintillation counter. Mean concentrations of total radioresidues are shown in Table VI.C.1.

 

 

Table VI.C.1. Mean Concentration (ng/g orppb) of Total Residue in Tissues of Cattle Following a Topical Dose of 5-3H-Eprinomectin at 500 mcg/kg bw
Tissue
Post Dosing Interval to Sampling (Days) - 7Post Dosing Interval to Sampling (Days) - 14Post Dosing Interval to Sampling (Days) - 21Post Dosing Interval to Sampling (Days) - 28
Liver977 ± 136751 ± 240465 ± 238185 ± 55
Kidney181 + 62121 ± 3970 ± 3030 ± 10
Fat34 ± 1522 ± 614 ± 85 ± 2
Dose site muscle24 ± 510 ± 419 ± 922 ± 28
Muscle8 ± 36 ± 24 ± 22 ± 0

Limit of detection varied from about 0.15 ppb to 0.16 ppb and limit of quantitation varied from about 0.27 ppb to 2.24 ppb. The total radioresidue concentrations in all edible tissues were already below their respective tissue-safe concentrations by 7 days post-treatment.

2.2 Residues in Tissues of One-Day Old Calves from Cows Dosed 7 - 14 Days Prior to Parturition with a Single Topical Application of Formulated 3H-MK-0397 (Trial CA-372, Protocol Number 4042).

a. Name and Address of Investigator:

 

 

Narayana I. Narasimhan
Merck Research Laboratories
P. O. Box 2000
Rahway, NJ 07065

b. Test Animals: Six near-term pregnant Holstein dairy cows were treated in this study.

c. Route of Drug Administration and Time and Duration of Dosing: Test animals were administered a single dose of eprinomectin topically at 750 mcg/kg body weight (1.5 x the use level) 7 to 14 days prior to parturition. The calves born to the dosed cows were sacrificed 12 to 24 hours after birth.

d. Radiotracer: The cows were dosed with a dosing solution containing 5-3H-MK-0397. The radiochemical purity of the drug substance was greater than 98% by high performance liquid chromatography. The topical solution used in this study was the same as the formulation to be marketed for use on cattle.

e. Milk and Tissue Sample Collection: Milk samples were collected at least once during the first 24 hours after parturition and every twelve hours from approximately 1.5 days through 7 days post parturition. Liver, kidney, fat, and muscle were collected from the calves. Milk and combusted tissue samples were subjected to radioactivity analysis using liquid scintillation spectrometry.

f. Total Residue Concentration: In colostrum and milk, peak radioresidue levels were in the range of 7.14 - 13.18 ng/mL (lower than the safe concentration of 16 ng/mL allowed in milk). The total residue levels observed in milk in study CA-372 were similar to or lower than the total milk residue levels observed in studies CA-365 and CA-367 described above. Total residue levels in fat and muscle of the calves were below the limit of quantitation (3.9 ppb for fat and 1.1 ppb for muscle). The total residue levels in kidneys were all equal to or below 2.0 ppb. The total residue levels in livers ranged from 5.8 ppb to 55.0 ppb and averaged 21.4 ppb.

3. Metabolism of Eprinomectin in Cattle.

Metabolite profiles in milk (Studies CA-365 and CA-367) and tissues and feces (metabolism study ADMES-3, samples from study CA-368) were determined. The radioresidues derived from eprinomectin and structurally similar metabolites were all essentially extractable into organic solvents. These solvent extracts were analyzed by reversed phase HPLC. Eprinomectin was not metabolized to a significant extent in lactating and beef cattle. The total amount of all the metabolites in the edible tissues or milk was 10% or less of the total radioresidues in any particular matrix. Also none of the metabolites was greater than 10% of the total radioresidues or was present in amounts greater than 0.1 ppm. Therefore, metabolites were not structurally identified. In general, the metabolite profile in a given matrix (tissues, plasma, or excreta) did not change with time post-dose in either dairy or beef cattle. Also, in beef cattle, the metabolite profiles in all matrices were independent of the sex of the animal. The metabolism of eprinomectin in all the biological matrices is nearly identical qualitatively and quantitatively.

Eprinomectin is not metabolized extensively in cattle and the B1a component is the major residue in all matrices. For example, in milk, liver, kidney, fat, dose-site muscle, and muscle, the percent contribution from the B1a component was 85.6, 86.4, 86.2, 86.7, 83.3, and 82.0, respectively. The percent contribution from eprinomectin and metabolite residues to the overall metabolite profile in milk, liver, fat, and feces are shown in Table VI.C.2.

 

 

Table VI.C.2. Percent Contribution of Eprinomectin and Metabolites to the Overall Metabolite Profile in Milk and Tissues
MatrixEprinomectinMetabolites
 B1b B1a Total
Milk7.985.693.5two metabolites > 1.0%
Liver9.386.495.7one metabolite 1.1%
Fat7.286.793.9one metabolite 1.0%
Feces8.378.386.6one metabolite 7.4%,
one metabolite 1.6%

D. Comparative Metabolism of Eprinomectin in Rats

1. The Distribution, Excretion, and Metabolism of MK-0397 (L-653,648) in Rats (ADMES-1).

a. Name and Address of Investigator:

 

 

Bruce A. Halley
Merck Research Laboratories
Box 2000
Rahway, NJ 07065

b. Test Animals: Sprague-Dawley (CRL-CD-SD BR) VAF rats (fourteen males and fourteen females), approximately seven weeks of age, were used in this study. The same strain of rats was treated in the fourteen-week and multigeneration oral toxicity studies and an oral developmental toxicity study.

c. Route of Drug Administration and Time and Duration of Dosing: Twelve animals of each sex were administered seven consecutive daily oral gavage doses of eprinomectin at approximately 6.0 mg/kg body weight. Two animals of each sex (controls) received approximately the same volume of unmedicated vehicle.

d. Radiotracer: The dosing solution contained 5-3H-L-653,648. The radiochemical purity of the drug substance was 98% by high performance liquid chromatography.

e. Samples Collected: Three male and three female rats were sacrificed at approximately 7 hours, 1, 2, and 5 days after the seventh dose. Liver, kidney, fat, muscle, and GI tract were collected. In addition, urine and feces were collected daily from each rat.

f. Results: Through day 5 after the last dose, 90% of the administered dose was excreted in feces and less than 1% in urine. Based on chromatographic retention times, the metabolite profiles in rat tissues and feces were shown to be qualitatively similar to the profiles in cattle milk, plasma, tissues, and feces. Although in most of the rat tissues, especially at later times, the percent contribution from one metabolite (M5, identified as the N-desacetyl MK-0397) was greater than 10%, metabolism of eprinomectin to M5 does not occur to any significant degree as a whole in the rat. This was based on the fact that in rat feces, where 90% of the dose was accounted for, M5 constituted only 1.5% and 6.2% of the total residues in males and females, respectively. All the metabolites that were observed in cattle tissues and milk were also observed in several rat tissues. Whereas the metabolism of eprinomectin was independent of sex in cattle, the metabolism of eprinomectin to M5 was sex-dependent in rats, i.e., the female rats produced more of M5. From this comparative metabolism study, it was evident that the rat, a laboratory toxicity test species, was exposed to the major drug residue components which were present in cattle tissues.

E. Selection of a Target Tissue, Marker Residue, and Determination of a Tolerance

Since the residue levels in liver were higher than those in other tissues and the total residue levels and the marker residue levels deplete in parallel in liver, liver was considered as the target tissue. Total residue levels in liver also depleted in parallel to total residue levels in other tissues.

Metabolite profiles of milk and other edible tissues indicated that the B1a component of eprinomectin was the major residue. The levels of the B1a component depleted in parallel to the total residues in all edible tissues, and was selected as the marker residue. Marker residue levels in milk and edible tissues were determined using the validated high pressure liquid chromatography-fluorescence detection method.

In studies CA-365 and CA-367, the peak levels of the marker residue in milk were in the range of 2.15 - 21.10 ng/mL. The ratios of marker residue levels to total eprinomectin-related residues (corrected for the contribution from tritiated water) at every milking interval were calculated and averaged to be 0.77. Hence, the tolerance of 12 ng/mL for the eprinomectin B1a component marker residue in milk was obtained by multiplying this ratio with the milk safe concentration of 16 ng/mL.

In study CA-368, the marker residue levels were determined in various edible tissues and are presented in Table VI.E.1.

 

 

Table VI.E.1. Marker Residue Levels (ng/g or ppb) in Edible Tissues of Cattle following a Topical Dose of 5-3H-Eprinomectin at 500 mcg/kg bw
Tissue
Post-Dosing Sample Interval (Days) - 7Post-Dosing Sample Interval (Days) - 14Post-Dosing Sample Interval (Days) - 21Post-Dosing Sample Interval (Days) - 28
Liver807 ± 168546 ± 185369 ± 194181 ± 70
Kidney161 ± 55113 ± 3554 ± 2324 ± 7
Fat30 ± 1119 ± 614 ± 85 ± 2
Dose-site muscle17 ± 48 ± 414 ± 612 ± 14
Muscle6 ± 34 ± 0.73 ± 1< 2

The ratio of marker residue concentration to the total residue concentration in each animal tissue was calculated and averaged for each tissue type. The average ratios in liver, kidney, fat, dose-site muscle, and muscle were 0.83, 0.85, 0.92, 0.71, and 0.69, respectively. The marker residue (eprinomectin B1a component) tolerance in the liver (target tissue) was calculated by multiplying the safe concentration in liver by the average ratio of marker to total residues in liver. Therefore, the tolerance in liver was 5760 ppb x 0.83, or 4800 ppb after rounding.

In study CA-372, marker residue levels in livers of one-day old calves were also determined. The marker residue levels in livers were averaged to be 19.3 ppb with a marker to total residue ratio of 0.90.

F. Studies to Establish a Withdrawal Time

1. Zero Milk Discard:

A zero milk discard has been established for IVOMEC® EPRINEX™ (eprinomectin) Pour-On for Beef and Dairy Cattle using 24 mcg of the total ADI for a person weighing 60 kg as the portion assigned to milk. This was based on the milk residue data from the radiotracer studies CA-365 and CA-367 as described in parts VI. C and VI. E of this summary.

2. Zero Tissue Withdrawal Period:

Three studies using the commercial pour-on formulation were conducted to demonstrate that no withdrawal period is required for edible tissues.

2.1 Eprinomectin (MK-0397): A Study in Cattle to Determine the MK-0397 Marker Residue for Establishing a Withdrawal Period (Study 94031, CA-371).

a. Name and Address of Investigator:

Study Director:

 

Lori D. Payne, Ph.D.
Merck Research Laboratories
Merck & Co., Inc.
P.O. Box 2000
Rahway, NJ 07065

Principal Biologist:

 

Terry D. Faidley, Ph.D.
Merck Research Laboratories
Merck & Co., Inc.
Somerville, NJ 08876

b. Test Animals: Seventeen male castrates and seventeen heifers, Hereford x Holstein, beef cattle weighing 436 to 656 kg and ranging in age from approximately 17 to 20 months were used in this study.

c. Route of Drug Administration: Thirty cattle were dosed by topical administration at 500 mcg/kg body weight (1 mL/10 kg body weight) with a solution containing 5 mg eprinomectin per mL of formulation (0.5%). The topical solution used in this study was the same as the formulation to be marketed for use on cattle. For calculation of the volume dosed, the animal's body weight was rounded up to the nearest 50 kg.

d. Time and Duration of Dosing: The cattle were treated once at Day 0. Five treated animals were sacrificed at each of six times post-dose: 10, 17, 24, 34, 44, and 55 days. Four animals served as unmedicated controls.

e. Results: Marker residue assays were conducted on the liver samples (the target tissue) and dose-site muscle using a validated high pressure liquid chromatography-fluorescence detection method. The average marker residue concentrations found are presented in Table VI.F.1.

 

 

Table VI.F.1. Average Marker Residue Concentrations (ng/g or ppb) in Liver and Dose-Site Muscle of Cattle Dosed Topically with Eprinomectin at 500 mcg/kg bw

Average Marker Residue Concentrations  
Post-Dose Sampling Interval (Days)
101724344455Control
ng/g (Liver)74823756264<1<1
Std. dev.7812528243------
ng/g (Dose-site muscle)83<2<1<1NA<1
Std. dev.22---------------
NA = not assayed

The analytical method used to determine the marker residue has a lower limit of reliable measurement of 2 ng/g and a limit of detection of 1 ng/g. The marker residue tolerance for eprinomectin-treated cattle has been established to be 4800 ng/g for liver. The average marker residue concentrations in liver from study CA-371 were at least six times lower than the liver tolerance.

2.2 Eprinomectin Topical: A Study in Cattle to Determine Eprinomectin (MK-0397) Marker Residue in Edible Tissue at 0.5, 1, 3, 5, and 7 Days After Treatment (Study 94458, ASR 14741).

a. Name and Address of Investigator:

Study Director:

 

Lori D. Payne, Ph.D.
Merck Research Laboratories
Merck & Co., Inc.
P. O. Box 2000
Rahway, NJ 07065

Principal Biologist:

 

Ron Gogolewski, Ph.D.
Merck Research Laboratories
Merck Sharp & Dohme Pty Ltd
P. O. Box 135
Ingleburn NSW 2565
Australia

b. Test Animals: Beef cattle (fourteen male castrates and thirteen heifers), of either Angus or Hereford breed, weighing 227 to 389 kg, and ranging in age from approximately 12 to 19 months were used in this study. The in-life phase was conducted in New South Wales, Australia.

c. Route of Drug Administration: Twenty-five cattle were dosed by topical administration at 500 mcg/kg body weight (1 mL/10 kg body weight) with a solution containing 5 mg eprinomectin per mL of formulation (0.5%). The topical solution used in this study was the same as the formulation to be marketed for use on cattle. For calculation of the volume dosed, the animal's body weight was rounded up to the nearest 50 kg.

d. Time and Duration of Dosing: The cattle were treated once at Day 0. Five animals were slaughtered at each of five times post-dose, 0.5, 1, 3, 5, and 7 days. Two animals served as unmedicated controls.

e. Results: Liver and dose-site muscle samples were assayed by the validated high pressure liquid chromatography-fluorescence detection method for marker residue. The average marker residue concentrations found are presented in Table VI.F.2.

 

 

Table VI.F.2. Average Marker Residue Concentrations (ng/g or ppb) in Liver and Dose-Site Muscle of Cattle Dosed Topically with Eprinomectin at 500 mcg/kg bw
Average Marker Residue Concentrations 
 
Post-Dose Sampling Interval (Days)
0.51357Control
ng/g (Liver)278551710376323<1
Std. dev.7114817713483---
ng/g (Dose-site muscle)<2342<2<1
Std. dev.---11---------
NA = not assayed

The criteria for a zero-withdrawal time were that the average marker residue concentration at each slaughter time in liver had to be no greater than one-half the liver marker residue tolerance of 4800 ppb. The criteria were met with this study, thus establishing a zero-withdrawal time for cattle. The average marker residue concentrations in dose-site muscle at all slaughter times were lower than 1/450 of the muscle safe concentration of 1920 ppb.

2.3 Eprinomectin (MK-0397): A Study in Non-ruminating Calves to Determine Eprinomectin Marker Residue Concentrations in Edible Tissues at 1, 3, 7, and 14 Days after Treatment (Study 94633, ASR 14645).

a. Name and Address of Investigator:

Study Director:

 

Lori D. Payne, Ph.D.
Merck Research Laboratories
Merck & Co., Inc.
Box 2000
Rahway, NJ 07065

Principal Biologist:

 

Terry D. Faidley, Ph.D.
Merck Research Laboratories
Merck & Co., Inc.
Somerville, NJ 08876

b. Test Animals: Fourteen preruminating male Holstein calves, weighing 90.4 to 103 kg and to be less than 16 weeks old at slaughter, were used in this study.

c. Route of Drug Administration: Twelve calves were dosed by topical administration at 500 mcg/kg body weight (1 mL/10 kg body weight) with a solution containing 5 mg eprinomectin per mL of formulation (0.5%). The topical solution used in this study was the same as the formulation to be marketed for use on cattle. For calculation of the volume dosed, the animal's body weight was rounded up to the nearest 10 kg.

d. Time and Duration of Dosing: The cattle were treated once at Day 0. Three treated calves were sacrificed at each of four times post-dose: 1, 3, 7, and 14 days. Two calves served as unmedicated controls.

e. Results: Marker residue assays were conducted on the liver samples (the target tissue), kidney, and dose-site muscle using a validated high pressure liquid chromatography-fluorescence detection method. The average marker residue concentrations found are presented in Table VI.F.3.

 

 

Table VI.F.3. Average Marker Residue Concentrations (ng/g or ppb) in Liver, Kidney, and Dose-Site Muscle of Calves Dosed Topically with Eprinomectin at 500 mcg/kg bw

Average Marker Residue Concentrations  
Post-Dose Sampling Interval (Days)
13714Control
ng/g (Liver)618832122080333
Std. dev.3771303864621
ng/g (Kidney)1191662371204
Std. dev.113481455--
ng/g (Dose-site muscle)9265723<1
Std. dev.111285--

The criteria for a zero-withdrawal time were that the average marker residue concentration at each slaughter time in liver had to be no greater than one-half the liver marker residue tolerance of 4800 ppb. The criteria were met with this study, thus establishing a zero-withdrawal time for preruminating cattle. The average marker residue concentrations in kidney and dose-site muscle at all slaughter times were lower than 1/45 of the kidney safe concentration of 11520 ppb and 1/30 of the muscle safe concentration of 1920 ppb, respectively.

G. Regulatory Methods

Because no withdrawal time applies to this product for either milk or edible tissues, no regulatory method is required. However, a determinative method using a high pressure liquid chromatography assay for the B1a component of eprinomectin has been validated in a sponsor-monitored method trial meeting CVM requirements. In addition, a validated research method for the B1a component of eprinomectin in milk has been made available by the sponsor.

H. User Safety

1. Acute Oral Toxicity Study in Mice

a. Report Number: TT #93-2733.

b. Study Dates: Started 21SEP93, ended 04OCT93.

c. Principal Investigators: W. Bagdon and M. Kloss.

d. Laboratory: Merck Research Laboratories, West Point, PA.

e. Substance and Dosage Form Tested: MK-0397 Cattle Topical Formulation (L-653,648-127C).

f. Species and Strain: Mouse, Crl:CD-1®(ICR)BR.

g. Number of Animals/Sex/Group: 10/sex.

h. Dosage Levels Tested: 5000 mg/kg (5.45 ml of formulation/kg body weight).

i. Route of Administration: Oral via gavage.

j. Parameters Examined: Physical signs of toxicity were recorded daily and body weights were recorded pretest and days 7 and 14.

k. Toxicity Observed: No mortality or treatment-related physical signs were observed in any mouse throughout the study.

l. No-Observed-Effect Level: > 5000 mg/kg (highest dose tested).

2. Ocular Irritation Study in Rabbits

a. Report Number: TT #93-2732.

b. Study Dates: Started 04OCT93, ended 18OCT93.

c. Principal Investigators: W. Bagdon and M. Kloss.

d. Laboratory: Merck Research Laboratories, West Point, PA.

e. Substance and Dosage Form Tested: MK-0397 Cattle Topical Formulation (L-653,648-127C).

f. Species and Strain: Rabbits, New Zealand White.

g. Number of Animals/Sex/Group: 2 males and 2 females per group.

h. Dosage Levels Tested: 0.1 ml of the formulation.

i. Route of Administration: Intraocular.

j. Parameters Examined: Daily examinations were conducted for systemic toxicity. Ocular examinations for signs of irritation were conducted for all animals 15 minutes and 2 hours after treatment on most days until study termination on day 15. One group received only the MK-0397 formulation while the other group received the formulation followed by rinsing the treated eye with approximately 20 ml of warm tap water 20 seconds following intraocular administration.

k. Toxicity Observed: Slight conjunctival redness was found in 1 of 4 rabbits in the unwashed group. This effect was completely reversible by 2 hours post-treatment. No other rabbits in this group or the group which received the water rinse showed any signs of irritation throughout the study.

3. Guinea Pig Dermal Sensitization Study

a. Report Number: TT #93-643-0.

b. Study Dates: Started 04OCT93, ended 03FEB94.

c. Principal Investigators: G. Durand-Cavagna.

d. Laboratory: Merck Research Laboratories, Chibret, France.

e. Substance and Dosage Form Tested: MK-0397 Cattle Topical Formulation (L-653,648-127C).

f. Species and Strain: Hartley albino guinea pigs.

g. Number of Animals/Sex/Group: 10 females in the negative control group, 11 females in each of the vehicle control and MK-0397-treated groups.

h. Dosage Levels Tested: 0.4 ml/treatment for induction, challenge, and re-challenge.

i. Route of Administration: Dermal.

j. Parameters Examined: Daily examinations for physical signs of toxicity and dermal irritation.

k. Toxicity Observed: Slight dermal irritation was found in the vehicle control and MK-0397-treated groups. However, the MK-0397 formulation is considered negative for dermal sensitization since on re-challenge, dermal signs were less than upon primary challenge and were similar in the vehicle and MK-0397 groups. The observed effects are considered due to the slight irritation produced by the formulation vehicle.

4. Thirty-Day Dermal Toxicity and Irritation Study

a. Report Number: TT #93-128-0.

b. Study Dates: Started 30SEP93, ended 07APR94.

c. Principal Investigators: M. Kloss, M. Hubert, and J. Majka.

d. Laboratory: Merck Research Laboratories, West Point, PA.

e. Substance and Dosage Form Tested: MK-0397 Cattle Topical Formulation (L-653,648-127C).

f. Species and Strain: Hanford mini-swine.

g. Number of Animals/Sex/Group: 4/sex/group.

h. Dosage Levels Tested: 5ml/animal/day for each of the saline control, vehicle control, and MK-0397 formulation groups.

i. Route of Administration: Dermal.

j. Parameters Examined: All animals were observed daily for physical signs and evidence of dermal irritation. In addition, all animals were weighed pretest and once weekly and food consumption was estimated twice daily. Complete necropsies were performed on all animals and the dermal application sites, brain, cervical spinal cord, and sciatic nerves as well as all gross changes from all animals were examined histopathologically.

k. Toxicity Observed: No treatment-related mortality, clinical signs, body weight or food consumption changes were found during the study. The only treatment-related finding was a slight increase in the incidence and severity of focal cellular infiltration noted histologically in the vehicle control and MK-0397-treated groups compared to the saline control. This finding is indicative of a mild degree of irritancy related to the formulation vehicle, since the presence of MK-0397 did not affect the incidence or severity of the response.

l. No-Observed-Effect Level: <5mL/dermal application site

5. Handler Safety Evaluation

The MK-0397 cattle topical formulation is not acutely toxic in mice as no toxicity was observed at 5000 mg/kg, the highest dose tested. The formulation was practically non-irritating to the eyes in the rabbit ocular irritation study. Irrigation of the eyes prevented the mild irritation that was observed. The formulation was not a dermal sensitizer in guinea pigs and did not produce any systemic toxicity when tested dermally in mini-swine. In one field trial, the person applying the drug did report a mild skin irritation on one hand which was directly exposed to the drug and was not immediately washed, however, this individual has a history of multiple hypersensitivities. The following direction is on the product:

As with any topical medication intended for treatment of animals, skin contact should be avoided. If accidental skin contact occurs, wash immediately with soap and water. If accidental eye exposure occurs, flush eyes immediately with water.

In addition, a toll-free telephone number will be available on the label to inform users of where to obtain additional information concerning user safety relative to the MSDS and to report adverse events involving the target species or human exposure.

VI. AGENCY CONCLUSIONS

The data submitted in support of this NADA satisfy the requirements of Section 512 of the Federal Food, Drug and Cosmetic Act and 21 CFR Part 514 of the implementing regulations. The data demonstrate that IVOMEC® EPRINEXTM Pour-On for Beef and Dairy Cattle is safe and effective for the treatment and control of gastrointestinal roundworms, lungworms, grubs, horn flies, lice and mange mites in cattle when administered topically as a single dose of 500 mcg eprinomectin per kilogram body weight. IVOMEC® EPRINEXTM Pour-On for Beef and Dairy Cattle has also been proven to protect cattle against infection or reinfection with Dictyocaulus viviparus for 21 days when administered at the recommended dose.

Based on a battery of toxicology tests, an acceptable daily intake (ADI) of 10 mcg/kg body weight/day was calculated. A portion of the ADI (0.4 mcg/kg body weight/day) was reserved for milk and yielded a milk safe concentration of 16 ppb. The rest of the ADI (9.6 mcg/kg body weight/day) was used in the calculation of safe concentrations for total eprinomectin-related residues of 1.92 ppm in muscle, 5.76 ppm in liver, 11.52 ppm in kidney, and 11.52 ppm in fat. Metabolism studies in cattle along with quantitation of a marker residue in radiolabeled milk and tissues established tolerances of 12 ppb and 4.8 ppm for the B1a component of eprinomectin (the marker residue) in milk and liver (the target tissue), respectively.

Based on the milk residue data from the radiotracer studies, a zero milk discard has been established for the use of IVOMEC® EPRINEX™ (eprinomectin) Pour-On product. There was no pre-slaughter withdrawal time required for edible tissues from the results of marker residue depletion studies in adult cattle and preruminating calves, following a single topical application of IVOMEC® EPRINEX™ (eprinomectin) Pour-On for Beef and Dairy Cattle at a dose rate of 500 mcg/kg animal body weight (1 mL/10 kg body weight).

The data submitted for IVOMEC® EPRINEXTM Pour-On for Beef and Dairy Cattle support the marketing of the product as an over-the-counter new animal drug. Adequate directions for use have been written for the layman, and the conditions for use prescribed on the labeling are likely to be followed in practice. Therefore, the Center for Veterinary Medicine (CVM) has concluded that this product shall have over-the-counter marketing status.

The Agency has carefully considered the potential environmental effects of this action and has concluded that the action will not have a significant impact on the human environment and that an environmental impact statement is not required. The Agency's finding of no significant impact (FONSI) and the evidence supporting that finding is contained in an environmental assessment which may be seen in the Dockets Management Branch (HFA-305), Park Building, (Room 1-23), 12420 Parklawn Dr., Rockville, Maryland 20857.

Under Section 512(c)(2)(F)(i) of the Federal Food, Drug, and Cosmetic Act, this approval qualifies for FIVE years of marketing exclusivity beginning on the date of approval because no active ingredient (including any ester or salt of the active ingredient) of the drug has been approved in any other application. IVOMEC® EPRINEXTM Pour-On for Beef and Dairy Cattle is under patent number 4,427,663, which expires on March 16, 2002 and patent number 5,602,107, which expires on May 10, 2013.

 

VII. APPROVED PRODUCT LABELING 

Copies of applicable labels may be obtained by writing to the:

Freedom of Information Office
Center for Veterinary Medicine, FDA
7500 Standish Place
Rockville, MD 20855