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U.S. Department of Health and Human Services

Animal & Veterinary

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NADA 140-857 Equestrolin™ - original approval

Approval Date: January 5, 1990

I. GENERAL INFORMATION:

NADA 140-857
Sponsor: Norden Laboratories, Inc.
Lincoln, NE 68501
Generic Name: luprostiol
Trade Name: Equestrolin™
Marketing Status:  

 

II. INDICATIONS FOR USE

Luprostiol is indicated for 1) estrus control and 2) termination of pregnancy in mares under the following conditions:

Estrus Control: Luprostiol is effective as a luteolysin and may be used to regress a functional, progesterone producing corpus luteum, subsequently inducing estrus, ovulation and normal conception in breeding mares under the following conditions:

  1. Estrus Control in Normal Cycling and Transitional Phase Mares:
    1. Normal cycling mares that demonstrate estrus activity may be treated to shorten the estrous cycle. Treatment should be given during the diestrus period when functional corpora lutea are present.
    2. Mares displaying estrous cycles, albeit erratic, may be treated if mature corpora lutea are present to shorten and/or reinitiate the estrous cycle.
  2. Estrus Control in Postpartum Mares:
    1. Postpartum mares that exhibit an overt foal heat but are not bred at this heat, in order to avoid reduced fertility, may be treated six to 12 days after the foal heat ovulation to attempt an early return to estrus ("second" foal heat) and subsequent breeding opportunity.
    2. Lactating mares that do not exhibit a foal heat and that are considered to be in lactational anestrus may be treated approximately 21 days postpartum in order to initiate estrus cyclicity.
  3. Estrus Control in Mares With Persistent Corpora Lutea:
    Mares not cycling due to a persistent corpus luteum (CL) may be treated to terminate functional luteal tissue. This would include:
    1. mares considered pseudopregnant (i.e., bred and determined not to be pregnant but displaying signs of pregnancy as a result of persistent CL activity).
    2. mares in clinical anestrus (i.e., not cycling during the breeding season due to persistent CL activity).
    3. mares that have lost a conceptus during early gestation and that have not recycled due to persistent CL activity.
    4. maiden and barren mares in extended periods of diestrus due to persistent CL activity.
  4. Termination of Pregnancy
    The luteolytic activity of luprostiol is also effective for the induction of abortion in mares pregnant for 36 days or less.

 

III. DOSAGE

A. DOSAGE FORM Luprostiol is a clear, colorless, sterile solution containing 7.5 mg of luprostiol per mL of propylene glycol.
B. ROUTE OF ADMINISTRATION Equestrolin is to be administered by intramuscular injection
C. RECOMMENDED DOSAGES: The dose is 7.5 mg (1 mL) per mare for the induction of fertile estrus or for abortion.

 

IV. EFFECTIVENESS

A. Estrus Control Claim

A dose determination study, two well controlled studies and 14 clinical field trials were conducted to determine the effectiveness of luprostiol for the induction of a fertile estrus in lighthorse mares. A list of investigators is provided in Table 1. Mares were administered an intramuscular injection of a prostaglandin control or luprostiol at the recommended use levels. In all studies, luteolysis was determined from the visual behavioral signs of estrus displayed by the mares post injection. In addition, serum progesterone concentrations were used in the dose determination and well controlled studies to confirm the luteolytic effect of the prostaglandin. The luteolytic property of the prostaglandins for estrus control was evaluated in 1) normal cycling and transitional phase mares, 2) postpartum mares, and 3) mares with persistent corpora lutea. For each study, posttreatment estrus, ovulation and conception rates were determined for the mares. Mares that subsequently displayed behavioral signs of estrus within six days post injection (PI) were categorized as animals that responded to treatment. The response rates calculated from the number of injections were 77.8% for the prostaglandin treated controls and 82.4% for the luprostiol-treated mares. The first-service conception of mares administered luprostiol was significantly improved in healthy, well-managed mares, especially for those mares considered difficult to breed (e.g., mares in the transitional phase, and mares anestrus during lactation or due to persistent luteal activity). The first-service conception rates for mares that responded to prostaglandin treatment were 56.2% for the controls as compared to 68.4% for luprostiol.

1. Pivotal Studies

Dose Determination Study

E.L. Squires, PhD
Colorado State University
Equine Sciences
Fort Collins, CO

A dose determination study was conducted to determine the effectiveness of luprostiol for inducing a fertile estrus in mares within 6 days postinjection. Healthy mares were allocated into 6 groups (20/group) and administered luprostiol at 0.00, 1.88, 3.75, 7.5 and 15.0 mg/head, or a prostaglandin control at the recommended dose. Following treatment, hormone profiles, indications of induced estrus, and subsequent ovulation and conception were monitored. Appropriate parametric (unpaired t-test) and non parametric (Mann Whitney) tests were used to compare the serum progesterone, LH and FSH concentrations between treatment groups (1). The Fisher's Exact test (1,2) was used to compare differences of nominal independent data between treatment groups regarding estrus induction, ovulation, first-service conception and embryo recovery. The Cochran-Armitage Linear trend test (3) was used to determine a linear trend between the treatment groups and fertile estrus (based on the total number of mares in each group). These tests were used in conjunction with biological advantage to determine the optimal dose.

The luprostiol dose which was effective in inducing estrus and achieving optimal first service conception following induced estrus (fertile estrus) was determined to be 7.5 mg/head. Although significant differences were not found among any of the potentially active luprostiol dosage groups (i.e., 1.88, 3.75, 7.5 and 15 mg.head) with respect to progesterone values, induced estrus rates, fertile estrus rates or subsequent ovulation, the 7.5 mg/head dose resulted in the highest fertile estrus rate suggesting a biological advantage over the other doses. On the basis of achieving an optimal rate of fertile estrus, as indicated by a first service conception rate of 72%, the dosage of 7.5 mg/head is the effective optimal dose of luprostiol for the mare for estrus control. In subsequent clinical field studies, luprostiol administered at 7.5 mg/head was equivalent to prostaglandin controls for estrus control.

  1. RS/1 Software by Bolt, Beranek and Newman Software Products Corp., Cambridge, MA.
  2. Kendall and Stuart, The Advanced Theory of Statistics (1960), Vol. II, pp 581-583.
  3. P. Armitage, Tests for Linear Trends in Proportions and Frequencies, Biometrics, September 1955, pp. 375-386.

Well-Controlled Studies

Two well-controlled studies were conducted at different geographical locations. Lighthorse mares (92) were administered an intramuscular injection of a positive control or luprostiol at the recommended use levels. Observed clinical signs of estrus and serum progesterone concentrations were used to confirm the effectiveness of the prostaglandins. The luteolytic properties of the prostaglandins for estrus control were evaluated in (1) normal cycling mares, (2) postpartum mares, and (3) mares with persistent corpora lutea. The individual investigator's efficacy results for these three indications are summarized in Table 2.

Serum progesterone concentrations were determined to confirm the luteolytic effectiveness of the two prostaglandin. Serum samples were collected from the mares prior to treatment (0 hour) and at 48 and 96 hours post injection, and mean progesterone values are summarized in Table 3.

Clinical Field Trials

Fourteen (14) field trials in different geographical locations were used to conduct the efficacy and safety evaluations of luprostiol in mares for estrus control. The results are listed in Table 2.

Summary of Effectiveness and Statistical Results

The overall effectiveness of luprostiol is displayed in the following table using two different observational units: (1) number of injections; and (2) number of mares. Some mares were administered more than one injection during the breeding season, as is normal practice. Only the initial injection and subsequent efficacy results were used for this summary of the data and thus, the number of mares was also considered the observational unit. The first service conception rates of the 2 treatment groups were statistically analyzed using the Fisher's Exact test.

(Eds. note: The following table consists of 3 columns.)

                                  Treatment Group*        
Observation unit              Control          Luprostiol

Number of Injections
 1. No. of Mares                   144                 370
 2. No. of Injections              176                 403
 3. No. Responding PI (%)           77.8                82.4
 4. Avg. Days to Estrus PI           3.4                 3.5
 5. Avg. Days to Ovulation PI        8.7                 8.6
 6. First Service Conception (%)    56.2(a)             68.4(b)
 
Number of Mares
 1. No. of Mares                   144                 370
 2. No. of Injections              144                 370
 3. No. Responding PI (%)           79.9                82.9
 4. Avg. Days to Estrus PI           3.3                 3.5
 5. Avg. Days to Ovulation PI        8.8                 8.7
 6. First Service Conception (%)    54.5(a)             68.7(b)

(ab) Means regarding percent conception on the same line with unlike superscripts are significantly different (P<0.05, Fisher's Exact test).

* Five (5) prostaglandin treated control mares and 20 Luprostiol-treated mares were excluded from the efficacy determinations for reasons which included: lack of estrus dates, anestrus mares, retained placenta, metritis, granulose cell tumor, cystic ovaries, endometrial cyst, under dose, or progesterone levels below 1 ng/ml at the time of injection. However, these mares were included in the overall safety analyses profile found in the following safety section. Data is summarized from a dose determination study, two well controlled studies, 12 controlled and 2 non-controlled clinical field trials.

The effectiveness of luprostiol to subsequently induce estrus, ovulation and normal conception in breeding mares is summarized under the following conditions: 1) normal cycling and transitional phase mares; 2) postpartum mares; and 3) mares with persistent corpora lutea. The number of injections was used as the observational unit.

(Eds. note: The following table consists of 3 columns.)

Category or Indication                   Treatment Group*        
   (parameter)                      Control          Luprostiol
Normal Cycling/Transitional Phase
  1. No. of Mares                          43                  143
  2. No. of Injections                     51                  154
  3. No. Responding PI (%)                 88.0                 87.9
  4. Avg. Days to Estrus PI                 3.4                  3.2
  5. Avg. Days to Ovulation PI              9.1                  8.4
  6. First Service Conception (%)          53.7                 67.6
Postpartum Mares
  1. No. of Mares                          52                  116
  2. No. of Injections                     62                  125
  3. No. Responding PI (%)                 73.3                 77.4
  4. Avg. Days to Estrus PI                 3.4                  3.9
  5. Avg. Days to Ovulation PI              8.3                  8.7
  6. First Service Conception (%)          63.6                 68.5
Mares with Persistent Corpora Lutea
  1. No. of Mares                          49                  110
  2. No. of Injections                     63                  122
  3. No. Responding PI (%)                 73.8                 80.2
  4. Avg. Days to Estrus PI                 3.3                  3.3
  5. Avg. Days to Ovulation PI              8.6                  8.7
  6. First Service Conception (%)          50.0(a)              69.2(b)

Note: Two luprostiol injections (or case reports) were not assigned to 1 of the 3 possible conditions (i.e., normal cycling/transitional phase mares, postpartum mares or mares with persistent corpora lutea) by the respective investigator. Therefore, the number of injections for each condition, when totalled in the overall summary, does not include these two case reports. Similarly, the number of mares for each condition, when totalled, does not include one of the unassigned case reports (the other case report involved a mare's second treatment).

The efficacy of luprostiol to induce estrus in "difficult to breed mares," i.e., transitional phase mares, postpartum mares treated for lactational anestrus and mares with persistent corpora lutea, is presented in the following table. This table excludes normal cycling mares and postpartum mares treated to induce a "second" foal heat.

(Eds. note: The following table consists of 3 columns.)

                                        Treatment Group*        
Difficult to Breed Mares    Control          Luprostiol

1. No. of Mares                    52                  145                
2. No. of Injections               66                  162                
3. No. Responding PI (%)           75.0                 77.9               
4. Avg. Days to Estrus PI           3.3                  3.4                
5. Avg. Days to Ovulation PI        8.4                  8.8                
6. First Service Conception (%)    51.3(a)              71.4(b)            

Summary of Progesterone Concentrations Progesterone profiles for mares from 4 investigations are provided below. Serum progesterone concentrations were used in the dose determination, the 2 well controlled studies, and the target animal safety study. These progesterone profiles, consistent with that expected of a fully effective equine prostaglandin, demonstrated the luteolytic effectiveness of luprostiol given at 7.5 mg to induce fertile estrus.

(Eds. note: The following table consists of 7 columns.)

Treatment    No.     Mean Serum Progesterone Level PI (ng/mL)
  Group     Mares     0 hr.    24 hr.   48 hr.    72 hr.    96 hr.
  
Placebo        15        8.26(a)    8.39(a)  11.73(a)   10.94(a)    ND*
Control #1     21        4.16(a)    ND        0.28(b)    ND         0.30(b)
Control #2     10       10.14(a)    2.10(b)   0.52(c)    0.47(c)    ND
Luprostiol     45        5.50(a)    1.32(b)   0.25(c)    0.28(c)    0.16(d)

(abcd)Means on the same line with unlike superscripts are significantly different (P<0.05, unpaired t-test or Mann-Whitney)

* ND = Not determined

2. Corroborative Studies Summary

Four investigations were conducted in Europe to evaluate the clinical effectiveness of luprostiol for use in mares. Dose response studies indicated that the optimal effective dosage of luprostiol for estrus control in the mare was 7.5 mg/head administered intramuscularly. European field use and drug tolerance studies demonstrated that luprostiol was highly efficacious and will tolerated for inducing fertile estrus. Studies to determine the effectiveness of luprostiol for estrus control indicated that a total of 137 mares given luprostiol at 7.5 mg./head, 110 (80%) came into estrus and of these 72 were successfully bred. Thus, a pregnancy rate of 65.5% was achieved in the mares which came into estrus following luprostiol treatment.

One clinical study conducted in the United States is also included in this section. Treatments were administered during mid to late September, a time of year when mares enter into season anestrus. Thus, low efficacy results were not unexpected. The results of this study to evaluate luprostiol for estrus control also included the determination of serum progesterone concentrations for mares of three separate experiments.

Individual Corroborative Studies

A. de Kruif
Boxmeer
The Netherlands

A pilot study to determine estrus induction in 28 mares was conducted in 27 Warmbloed Paardenstamboek Nederland (W.P.N.) breed mares and one heavy draught Belgian mare using luprostiol at 5.625 mg/head. The mare's body weights ranged from 450 to 750 kg. Nineteen mares were initially treated with 5.625 mg luprostiol. No rectal examination before treatment was performed, nor plasma progesterone values determined. Therefore, the study was not designed to show 100% estrus induction because this compound can only be effective in the presence of a functional corpus luteum. Of these 19 mares, 14 came into heat (showing clinical signs of estrus) within 4 days post injection, 13 were serviced and 7 became pregnant. The remaining 5 mares were treated with another dose of 5.625 mg luprostiol 7 days later, 1 mare came into heat and was serviced but did not conceive. Three (3) of the 4 remaining mares were dosed for a third time. All 3 mares exhibited signs of heat by the fourth day post injection, all were serviced, and 1 mare became pregnant.

A second group of 9 mares which had been serviced and were negative with the rectal pregnancy test were treated. After they were administered luprostiol, all mares exhibited estrus. Six (6) of the mares were serviced and 5 conceived.

No side effects were observed in the treated horses from either group.

Drs. A. Wilderbeek and Ir. A.J. Mul
Boxmeer
The Netherlands

A dose titration study involving 30 cases of luprostiol treated mares of W.P.N. and Arabian breeds, ranging from two to 11 years and body weights of 532 to 725 kg., were administered intramuscularly 1 ml of one of the following concentrations: 0.47 mg/ml, 0.94 mg/ml, 1.88 mg/ml, 3.75 mg/ml or 7.5 mg/ml. An additional untreated control group was also used with plasma progesterone levels determined for all treatment groups on day 0, day 1, day 3, day 8-10, and day 14. Results indicated that the optimal effective dosage of luprostiol for estrus control in the mare is 7.5 mg/head administered intramuscularly.

Dr. A. Wilderbeek
Boxmeer
The Netherlands

The first clinical trial involving 31 mares at one farm of mostly New-Forest ponies and Arabian breeds, were administered 1 ml (7.5 mg) luprostiol intramuscularly which resulted in 67% of the mares having estrus induced within seven days, of which 20 were serviced and 18 became pregnant. The second clinical trial involved 4 Haflingers (dosed with 3.75 mg/head), one riding horse and one heavy draught horse each dosed with 1 ml(7.5 mg/head) luprostiol intramuscularly. The results showed 100% estrus induction and 100% conception. Sweating was observed in one mare of the 37 luprostiol-treated mares.

Drs. A. Wilderbeek
Drs. S. Theunissen
Baarn
The Netherlands

A clinical trial was conducted using luprostiol in field use conditions located on stud farms and private residences. Forty (40) horses were treated for one of the following indications: 1) suboestrus, 2) second foal heat (the induction of estrus 20 days after parturition), 3) induction of estrus after embryonic death, and 4) partus induction. Mares of various breeds (W.P.N. breed, Hackney, Standardbred, Arabian and English thoroughbred), ages (4 to 23 years) and weights (400 to 750 kg) were administered 7.5 mg luprostiol to treat these disorders. Excluding the indication of partus induction, a total of 37 horses were treated, 35 came into heat, 31 were serviced, and 19 became pregnant within the first two cycles after luprostiol treatment. None of the mares treated showed any side effects.

E.L. Squires, PhD
Colorado State Univ.
Equine Sciences
Fort Collins, CO

One clinical study conducted in the United States was included in this section. Treatments were administered during mid to late September, a time of year when mares enter into seasonal anestrus. Thus, low efficacy results were not unexpected. The results of this study to evaluate luprostiol for estrus control also included the determination of serum progesterone concentrations for mares in three separate experiments. These results are summarized below:

(Eds. note: The following table consists of 5 columns.)

Serum progesterone:
                                            Mean Serum Progesterone
                                                Level PI (ng/mL)
Category of Mare   Treatment Group  No. Mares  0 hour      72 hour
Normal Cycling        Control               16        4.53          0.05
                      Luprostiol            15        3.78          0.08
Normal Cycling        Placebo               12        5.99          5.45
                      Luprostiol             9        5.46          0.30
Persistent Corpus     Control               13        1.14          0.04
   Luteum             Luprostiol            13        1.31          0.04

(Eds. note: The following table consists of 4 columns.) 

Induced estrus response:
                                                No. Responding Within
Category of Mare   Treatment Group  No. Mares      7 Days PI
Normal Cycling        Control               16           69% (11/16)
                      Luprostiol            15           60% (9/15)
Normal Cycling        Placebo               12            0% (0/12)
                      Luprostiol             9           44% (4/9)
Persistent Corpus     Control               13           31% (4/13)
Luteum                Luprostiol            13           38% (5/13)

B. Abortion Claim 1. Pivotal Studies

A dose confirmation study and 4 clinical field trials were conducted to evaluate the effectiveness of luprostiol for termination of pregnancy in mares. A list of investigators is provided in Table 1. The same dose of 7.5 mg per mare was determined to be effective for the abortion claim. A study was designed to confirm this efficacy and the conclusion was that luprostiol was highly effective and safe as an equine abortifacient when administered as a single injection through 36 days of gestation.

Dose Confirmation Study

E.L. Squires, PhD
Colorado State Univ.
Equine Sciences
Fort Collins, CO

The clinical efficacy and safety of luprostiol for induced abortion was evaluated in 48 Appaloosa, Quarterhorse and Thoroughbred mares in northeastern Colorado. This study was designed to confirm that 7.5 mg/head was efficacious as an equine abortifacient. Mares pregnant for approximately 33 days were administered an intramuscular injection of placebo (i.e., propylene glycol), a prostaglandin control or luprostiol. Efficacy and safety results for these three treatment groups are summarized below:

(Eds. note: The following table consists of 4 columns.)

                            ---------Treatment Group---------
Parameter                   Placebo     Control     Luprostiol
No. Animals                       15            16            17            
Average Gestation (days)          33.6          33.0          32.8          
Number Abortions PI (%)           20.0          93.8         100.0         
Average Days to Abortion PI        6.3           4.7           4.3           
Complications Postabortion (%)     0.0           0.0           0.0         

Serum progesterone concentrations were determined in order to confirm the luteolytic effectiveness of the placebo and two prostaglandins. Serum samples were collected from the mares prior to treatment (0 hour) and at 24, 48 and 96 hours post injection, and mean progesterone values for the 3 treatment groups are summarized below:

(Eds. note: The following table consists of 5 columns.)

                      Mean Progesterone Levels (ng/mL)
Treatment Group   0 hour    24 hour    48 hour    96 hour
Placebo             4.49(a)     3.64(a)      4.55(a)     4.99(a)
Control             5.75(a)     1.45(b)      0.99(b)     1.39(b)
Luprostiol          5.98(a)     1.00(b)      0.55(b)     0.47(b)

(ab)Means in columns with unlike superscripts are significantly different
(P<0.05, unpaired t-test or Mann-Whitney)

These progesterone profiles, consistent with that expected of a fully effective equine prostaglandin, demonstrated the luteolytic effectiveness of luprostiol given at 7.5 mg as an equine abortifacient. Clinical Field Trails

D. Meyer, DVM
Route 2
Muscoda, WI

The clinical efficacy and safety of luprostiol to induce abortion was evaluated in 2 mares. Each mare given a single injection of luprostiol on day 16 of gestation aborted without complications. The actual day of abortion was not recorded for these 2 mares. No side effects were reported for either mare administered luprostiol.

R.S. Lacy, DVM
Box 1398
Vernon, TX

The clinical efficacy and safety of luprostiol to induce abortion was evaluated in 1 mare. The mare given a single injection of luprostiol on day 30 of gestation aborted without complications by day 4 post injection. No side effects were reported.

D. Rollins, DVM
F. Boweres, DVM
300 South Hammons
Springfield, MO

The clinical efficacy and safety of luprostiol to induce abortion was evaluated in 1 mare. One mare given a single injection of luprostiol on day 62 of gestation did not abort. No side effects were reported.

E. Stencel, DVM
PO Box 127
Curtis, NE

The clinical efficacy and safety of luprostiol to induce abortion was evaluated in 1 mare. The mare given a single injection of luprostiol on day 36 of gestation aborted without complications by day 4 postinjection. No side effects were reported.

Summary

Luprostiol was evaluated in 1 dose confirmation and 3 clinical field trials as an equine abortifacient. Overall results indicated that this prostaglandin was highly effective and safe when administered as a single injection through 36 days of gestation. These results are summarized below:

(Eds. note: The following table consists of 5 columns.)

           No. of Luprostiol   Gestation       No. Abortions   Average Day to
No. Mares     Injections      Range(days)      Postinjection    Abortion
 21                 1                 <36              21 (100.0%)       4.3 (N=19*)      

* Actual day of abortion was not reported for 2 mares

2. Corroborative Studies

Ir. A. Mul
Boxmeer
The Netherlands

Twelve pony mares, pregnant for 106 to 152 days, were given luprostiol for the termination of pregnancy in a clinical trial. Eleven of the 12 (92%) aborted after an average of 3 injections. No evidence of side effects, retained placenta nor endometritis were observed after abortion on the 11 mares. Three months post abortion the mares were observed for estrus and bred, and within 8 months post abortion 10 of the 11 mares (91%) were again pregnant. The 12th mare did not abort after 5 injections and subsequently gave birth to a healthy foal. This mare did show signs of sweating and increased respiration after receiving multiple injections.

 

V. SAFETY PROFILE

A. Pivotal Studies

A target animal safety study, 2 nursing foal safety studies and 14 clinical field trials have been conducted to provide information for the safety of luprostiol in mares.

Target Animal Safety Study

John M. Murphy and Lyn Jensen
Norden Laboratories
Lincoln, NE

A toxicity/safety study was conducted to determine the effect of luprostiol when administered to mares at 1X, 3X and 5x the proposed use level (7.5 mg per mare). Additionally, a group of control mares were each administered a 5 ml placebo containing propylene glycol (i.e., equivalent to the volume of vehicle given to mares that received luprostiol at 5x). The test articles were administered by intramuscular injection once daily for three consecutive days. Appropriate parametric (unpaired t-test) and nonparametric (Mann-Whitney) tests were used to compare the serum progesterone, clinical chemistry, hematology, body weights and feed consumption data(1). The Fisher's Exact test (1,2) was used to compare differences of nominal independent data between treatment groups. In summary, the administration of luprostiol at 1x, 3x, or 5x the recommended level produced little overt effect.

No dose-response trend was apparent with respect to changes in body temperature following any of the 1x, 3x or 5x injections. A decrease in the percentage of eosinophils was observed after each injection, irregardless of the luprostiol treatment group observed. However, the eosinophil counts returned to baseline within 24 hours postinjection. No dose response relationships were detected for the remaining hematological or clinical chemistry parameters. Ovarian follicular fluid increased as the dose of luprostiol was increased. However, this is not considered pathologically significant since one of the effects of luprostiol is accelerated ovulation. Therefore, the increase in follicular fluid was judged to represent a more mature preovulatory follicle in the mares receiving increased dosages of luprostiol. Hyperglycemia, dyspnea, hypergastric motility and hyperthermia were not observed in mares given luprostiol up to 5X the recommended dose for three consecutive days. Gross and macroscopic evaluation of tissues from mares administered luprostiol at 1x, 3x, or 5x the recommended level revealed no drug related lesions at the conclusion of the study.

Foal Safety Studies

M.L. Sharp, DVM
Box 353
Vernon, TX

Two separate trials were conducted to evaluate the clinical safety of luprostiol in 28 healthy foals. Either 7.5 mg/head or 15 mg/head of luprostiol was administered by intramuscular injection to each postpartum mare with a nursing foal.

Sixteen (16) healthy foals were observed in the first trial. Four (4) postpartum mares with nursing foals were each administered a 1 ml intramuscular injection of a placebo (i.e., propylene glycol). Eight postpartum mares with nursing foals were each administered a 1 ml intramuscular injection of luprostiol (7.5 mg/head).

Each foal was continuously observed 24 hours prior to treatment of its dam and through 24 hours post-treatment. The following parameters were measured: (1)rectal temperature, (2) heart rate; (3) respiratory rate; (4) intestinal sounds; (5) frequency of defecation; (6) stool consistency; (7) frequency of micturition; (8) frequency of nursing; (9) frequency of lying down and duration.

The observed parameters were considered normal for all 16 foals during the 48 hour observation period. No adverse reactions were reported for any of the foals and no effect on their overall functions or behavior was noted. Therefore, nursing foals were not affected when their dams were intramuscularly administered 1 ml (7.5 mg) of luprostiol.

In the second trial, 12 healthy foals were observed. Four postpartum mares with nursing foals were each administered a 2 ml intramuscular placebo (i.e., propylene glycol). Eight postpartum mares with nursing foals were each administered 2 ml (2x the recommended use level) luprostiol intramuscularly at a concentration of 7.5 mg/ml.

Each foal was continuously observed 24 hours prior to treatment of its dam and through 24 hours post treatment. Daily observations of each foal were continued for 30 days post treatment of its dam. The same parameters, previously mentioned, were measured for each foal beginning 24 hours prior to treatment of its dam and continuing for 96 hours post treatment of its dam.

In addition, clinical tests that included hematology, blood and serum chemistries were performed on blood drawn from each foal at 24 hours prior to treatment of its dam and then at 0 hour and 1, 4, 8, 12, 24, 48 and 96 hours post treatment of its dam. Also, a urinalysis and fecal examination for each foal was conducted at 24 hours prior to treatment of its dam and then at 0 hour and 24, 48 and 96 hours post treatment of its dam.

The observed parameters were considered normal for all 12 foals during the 30 day post treatment observation period. No adverse reactions were reported for any of the foals and no effect on their overall functions or behavior was noted. No systemic signs of toxicity or adverse effects were noted in the blood, urine or fecal analyses.

In summary, nursing foals were not affected when their dams were treated with either 1x or 2x the recommended dose (7.5 mg/head) of luprostiol.

Clinical Safety - Summary

Information regarding the safety of luprostiol administered at the recommended use level of 7.5 mg for estrus control or abortion was collected during the clinical efficacy field program. No drug interactions were reported between luprostiol and the standard therapy in the management or treatment of mares. Standard animal health products included antibiotics, anthelmintics and therapies to induce ovulation (e.g., GnRH, HCG). Post treatment conception rates, particularly first service conception, were highly successful in the luprostiol treated mares. Therefore, it was demonstrated that luprostiol had no adverse affect on conception and that the reproductive competence of these mares was not only maintained, buy may have been improved.

A summary of the percentage of side effects observed during clinical field trials evaluating luprostiol for estrus control and abortion is provided below:

(Eds. note: The following table consists of 5 columns.)

Treatment                                Side Effects Observed PI    
Group       No. Mares   No. Injections    Number      Percent
Control #1      135             165             94/165          57.0%           
Control #2      25              27              0/27            0.0%            
Luprostiol      392             425             19/425          4.5%          

B. Corroborative Studies Mutagenicity Studies

The mutagenicity of luprostiol was evaluated in the following tests:

  1. Salmonella/mammalian: Microsome Mutagenicity Test (Ames Test), H.P.F. Joosten, Scientific Development Group, Organon, Oss, The Netherlands
  2. Micronucleus Test in Rats, H.P.F. Joosten, Scientific Development Group, Organon, Oss, The Netherlands
  3. L5178Y TK+/-Mouse Lymphoma Mutagenesis Assay, Paul Kirby, Microbiological Assoc., Bethesda, MD
  4. Unscheduled DNA Synthesis in Rat Primary Hepatocytes, A. Thilagar, Microbilogical Assoc., Bethesda, MD

A negative response was produced in each study and it was concluded that luprostiol was not a potential mutagen.

Oral Toxicity Study in Rats

Crosby Thompkins
Toxicity Research Labs
Muskegon, MI

Four groups of Crl:CD® (SD) BR rats (20/sex/group) were dosed orally by gavage once daily with 0.00, 0.10, 3.00, or 100.00 mg/kg/day of luprostiol until the day of necropsy. Body weights and food consumption were recorded. Administration of 100 mg/kg/day of luprostiol to rats for 13 weeks produced retained corpora lutea, hematopoiesis of the spleen and liver, nephrosis and interstitial nephritis, degeneration of the harderian gland, excessive formation of bone trabeculae and osteoid tissue in the femur, excessive formation of osteoid tissue and/or callus in the tibia/fibula, and fractures of the tibia/fibula. (Formation of callus in the tibia/fibula is considered to be an attempt by the body to heal the fractures). Administration of 3.00 mg/kg/day of luprostiol produced some retention of corpora lutea but no other treatment related effects. Administration of 0.10 mg/kg/day of luprostiol produced no treatment-related effects.

Oral Toxicity Study in Dogs

Crosby Thompkins
Toxicity Research Labs
Muskegon, MI

Four groups of beagle dogs (6/sex/group) were dosed once daily with 0.0, 0.025, 0.250 and 2.500 mg/kg of luprostiol until their day of necropsy during week 14. Administration of luprostiol at the 2.500 mg/kg/day dose level produced multifocal serositis in the liver, associated with changes in some clinicopathologic parameters. Other effects were transitory lower body weight gain and food consumption averages, and several clinical signs which decreased in frequency as the study progressed. The only effects seen at the 0.250 mg/kg/day dose level were a higher mean adrenal weight in treated males than in the control group and observed vasculitis, mainly of the central vein of the liver, in 50% of the males and 17% of the females. No effects of toxicological significance were seen at the 0.025 mg/kg/day dose level.

Teratogenicity Study in Rats

Mildred Christian
Argus Research Labs, Inc.
Perkasie, PA

Luprostiol was administered orally via gavage to presumed pregnant rats on day six through 15 of gestation at dosages of 0 (vehicle), 0.12, 1.20, 12.00 or 2500.00 µg/kg/day. The dosage volume administered (5 ml/kg) was adjusted daily for observed body weights. The dams were sacrificed, and the fetuses were Caesarean-delivered on day 20 of presumed gestation.

Embryo/fetal effects occurred only at the abortifacient 2500.00 µg/kg/day dosage. Most of these effects could not be distinguished from the maternal effects of the test article and included increased resorption, fetal death and decreased litter size. The adult and developmental NOEL were determined to be 12.00 µg/kg/day.

Multigeneration Study in Rats

Mildred Christian
Argus Research Labs, Inc.
Perkasie, PA

Luprostiol was administered via gavage once daily to F0 Generation Crl:COBS® (SD)BR male and female rats at dosages of 0 (vehicle), 0.10, 1.00, 10.00 or 2500.00 µg/kg/day. Dosages were administered to the second parental generation rats (F1b Generation).

The 2500.00 µg/kg/day dosage was toxic to the first parental generation of rats. Toxic effects of this dosage of luprostiol included death, clinical signs, gross lesions and inhibited body weight gain. This toxic dosage also resulted in adverse effects on reproduction including decreased fertility, abortion and decreased viability of offspring. As compared with control values, no adverse, dosage dependent toxic or adverse reproductive effects were observed for the 0.10, 1.00, or 10.00 µg/kg/day dosage group first (F0) or second (F1b) generation adults or their offspring (F1a, F1b, F2a and F2b litters). Thus, the NOEL was determined to be 10 µg/kg/day.

 

VI. HUMAN SAFETY

Data on the safety of human consumption of drug residues in food were not required for this NADA. Luprostiol is intended for use only in horses, and is not intended for human consumption and is labeled: NOT FOR USE IN HORSES INTENDED FOR FOOD.

Human safety relative to handling and administration of this product is provided in the labelling, as follows: Women of childbearing age, asthmatics, and persons with bronchial and other respiratory problems should exercise extreme caution when handling this product. In the early stages, women may be unaware of their pregnancies. Luprostiol is readily absorbed through the skin and can cause abortion and/or bronchiospasms. Direct contact with the skin should therefore be avoided. Accidental spillage on the skin should be washed off immediately with soap and water.

 

VII. AGENCY CONCLUSIONS

The data submitted in support of this NADA comply with the requirements of Section 512 of the Act and Section 514.111 of the implementing regulations. It demonstrates Equestrolin (luprostiol) when used under its labeled conditions of use is safe and effective.

For the safe and effective use of Equestrolin it is necessary to provide a differential diagnosis of the reproductive status of the ovaries per rectal palpation which only a trained professional can accomplish. Additionally, professional expertise is required to determine the duration of pregnancy in those mares to be aborted since the drug is very efficacious up to 36 days of pregnancy. Accordingly, we have classified Equestrolin as a prescription item.

(Eds. note: The following table consists of 3 columns.)

Table 1 Identification of Investigators, Trial Locations and Study Types  for the Efficacy and Safety Studies Using Luprostiol 

Investigator            Location/Address        Type of Study
____________________________________________________________________________
E.L. Squires, PhD          Colorado State             Dose Determination for     
                           University Fort Collins,   Estrus Control             
                           CO 80523                                              
M.P. Reid, DVM             Route 1 Pendleton, SC      Well-controlled estrus     
                           29670                      control  study             
H.S. Conboy, DVM           1335 Harp Innis            Well-controlled estrus     
                           Lexington, KY 40511        control trial              
R.J. Krieg, DVM            Rt 2, Box 8 Killdeer, ND   Estrus control trial       
                           58640                                                 
D. Hamm, DVM               Route 13, Box 203          Estrus control trial       
                           Fayetteville, AR 72701                                
J.S. Fleming, DVM C.       5019 West Street Ocala,    Estrus control trial       
Roberts, DVM               FL 32674                                              
G.G. Duskin, DVM           11308 State Route 2        Estrus control trial       
                           Snohomish, WA 98290                                   
J. Newman, DVM             3518 1st Avenue North      Estrus control trial       
                           Great Falls, MT                                       
J. Melton, DVM             Harrison Animal Clinic     Estrus control trial       
                           Route 8 Harrison, AR                                  
                           72601                                                 
P. Lieux, DVM              4728 Riverview Drive       Estrus control trial       
                           Riverside, CA 92509                                   
A.R. Balay, DVM            7401 Dixboro Road South    Estrus control trial       
                           Lyon, MI 48178                                        
D. Meyer, DVM              Riverdale Vet. Clinic      Estrus control and         
                           Rural Route 2 Muscoda,     abortion trial             
                           WI 53573                                              
R.S. Lacey, DVM            P.O. Box 1398 Vernon, TX   Estrus control and         
                           76384                      abortion trial             
D. Rollins, DVM F.        3230 E. Lombard            Estrus control and         
Bowers, DVM                Springfield, MO 65802      abortion trial             
E. Stencel, DVM            P.O. Box 127 Curtis, NE    Estrus control and         
                           69025                      abortion trial             
E.L. Squires, PhD          Colorado State             Dose Confirmation study    
                           University Fort Collins,   for induced abortion       
                           CO 80532                                              
H.P.F. Joosten             Scientific Development     Mutagenicity, Ames Test    
                           Group Organon, Oss The                                
                           Netherlands                                           
Paul Kirby, PhD            Scientific Development     Mutagenicity,              
                           Group Organon, Oss The     MicronucleusTest           
                           Netherlands                                           
A. Thilagar, PhD           Microbiological Assoc.    Mutagenicity, Lymphoma     
                           5221 River Road            Mutagenesis Assay          
                           Bethesda, MD 20816                                    
Crosby Thompkins, PhD      Toxicity Research Labs     Oral Toxicity in Rats      
                           510 West Hackley Ave.                                
                           Muskegon, MI 49444                                    
Crosby Thompkins, PhD      Toxicity Research Labs     Oral Toxicity in Dogs      
                           510 West Hackley, Ave.                               
                           Muskegon, MI 49444                                    
Mildred Christian, PhD     Argus Research Labs        Teratogenicity in Rats     
                           Perkasie, PA 18944                                    
Mildred Christian, PhD     Argus Research Labs        Multigeneration in Rats    
                           Perkasie, PA 18944                                    
M.L. Sharp, DVM            P.O. Box 353 Vernon, TX    Two safety studies in      
                           76384                      foals                      
John M. Murphy, MS Lyn     Norden Laboratories 601    Target Animal Safety       
Jensen, DVM                W. Cornhusker Hwy.                                   
                           Lincoln, NE 68521                                   

(Eds. note: The following table consists of 9 columns.)

Table 2. Efficacy Evaluation of Luprostiol.

                       Percent       Days to         Days to        First                                  Percent
              No.     Responding     Estrus         Ovulation      Service      Seasonal    No. Services    Side
Compound    Animals  to Treatment  Postinjection  Postinjection  Conception %  Pregnancy %  per Pregnancy  Effects*
                                                           WELL-CONTROLLED STUDIES
                                                          Investigator: M P Reid, DVM
Control         16          84.2            4.1              9.7             73.3           87.5            1.3          100.0(2)
Luprostiol      16          82.4            3.9              8.8             61.5           81.3            1.2            0.0
                                                          Investigator: H S Conboy, DVM
Control         14          93.3            2.7              7.4             54.5           75.0            1.3           86.7(1)
Luprostiol      46          86.0            3.3              7.8             64.9           80.5            1.2            2.0(3)
                                                           CLINICAL FIELD TRIALS
                                                          Investigator: R J Krieg, DVM
Control          5         100.0            2.7              7.2             66.7          100.0            1.5          100.0(1)
Luprostiol      19          86.4            3.3              9.1             88.9          100.0            1.1           69.6(1)
                                                          Investigator: D Hamm, DVM
Control          7          71.4            4.2             11.8             80.0           71.4            1.0            0.0
Luprostiol      15          80.0            4.5             11.3             91.7           93.3            1.1            0.0
                                                          Investigator: J S Fleming, DVM; C Roberts, DVM
Control          6          62.5            3.8              9.0             60.0           80.0            1.3            0.0
Luprostiol      10          57.1            3.0              6.0             75.0           87.5            1.1            0.0
                                                          Investigator: G G Duskin, DVM
Control          5          57.1            2.8              7.3             50.0           75.0            1.3            0.0
Luprostiol       9          71.4            3.7              9.2             80.0           87.5            1.1            0.0
                                                          Investigator: J Newman, DVM
Control          1         100.0            5.0             10.0              0.0            0.0            0.0            0.0
Luprostiol       8         100.0            3.8              7.0             40.0           33.1            1.0            0.0
                                                          Investigator: J Melton, DVM
Control          1         100.0            3.0              6.0              0.0            0.0            0.0            0.0
Luprostiol       4         100.0            3.3              6.5            100.0          100.0            1.0            0.0
                                                          Investigator: P Lieux, DVM
Control         34          75.5            3.4              7.7             55.9           90.6            1.5           52.0(1)
Luprostiol      42          80.0            3.7              8.0             60.0           80.0            1.6            0.0
                                                          Investigator: A R Balay, DVM
Control          1         100.0            4.0              9.0            100.0          100.0            1.0          100.0(1)
Luprostiol       6          75.0            5.0              8.0             50.0           66.7            1.0            0.0
                                                          Investigator: D Meyer, DVM
Control          9          88.9            3.0              7.5             87.5           77.8            1.0           66.7(1)
Luprostiol      33          93.8            3.8              8.5             70.0           74.2            1.0            0.0
                                                          Investigator: R S Lacy, DVM
Control         11          50.0            2.3             15.4             50.0           71.4            1.2           69.7(1)
Luprostiol      27          80.8            3.4             10.1             81.0           84.9            1.1            0.0
                                                          Investigator: D Rollins, DVM; F Bowers, DVM
Control          7          88.9            2.8             ND               16.7           25.0            1.0           55.6(4)
Luprostiol      21          91.3            2.8             ND               53.3           53.3            1.0            0.0
                                                          Investigator: E Stencel, DVM
Control          7          71.4            4.0             ND                0.0           33.3            1.0           75.0(1)
Luprostiol      38          66.7            3.3             ND               51.7           62.9            1.1            0.0
                                                          Investigator: E L Squires, PhD
Control          0
Luprostiol      53          84.0            3.0              8.0             69.0           70.6            1.2            2.5(5)
                                                          Investigator: J L Manning DVM
Control          0
Luprostiol       3         100.0            4.5              8.8            100.0          100.0            1.0            0.0

ND = Not Dmtermined

* Side effects were calculated from the number of injections. The side effects listed in parenthesis are:

  1. sweating
  2. sweating and/or increased respiration
  3. small cutaneous edema
  4. sweating and/or colic
  5. mild discomfort and/or slight sweating

(Eds. note: The following table consists of 5 columns.)

Table 3 Serum Progesterone Concentrations

                                  Mean Progesterone Levels (ng/mL)    
Investigator    Treatment Group  0 Hour      48 Hour     96 Hour
M.P. Reid, DVM     Control            3.65          0.25          0.31            
                   Luprostiol         4.16          0.12          0.05            
H.S. Conboy, DVM   Control            8.97          0.52          0.18            
                   Luprostiol         5.84          0.31          0.41       

 

VIII. LABELING (Attached)

  1. Equestrolin(TM) Package Insert
  2. Equestrolin(TM) Vial Label 1mL
  3. Equestrolin(TM) Carton Label 10-1mL vials
  4. Equestrolin(TM) Vial Label 10mL
  5. Equestrolin(TM) Carton Label 1-10mL vial
  6. Equestrolin(TM) Vial Label 20mL
  7. Equestrolin(TM) Carton Label 1-20mL vial

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

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