• Decrease font size
  • Return font size to normal
  • Increase font size
U.S. Department of Health and Human Services

Animal & Veterinary

  • Print
  • Share
  • E-mail

NADA 141-074 Trexonil™ - original approval

Approval Date: December 23, 1996

I. GENERAL INFORMATION:

NADA141-074
Sponsor:Wildlife Laboratories, Incorporated
1401 Duff Drive, Suite 600
Fort Collins, Colorado 80524
Generic Name:naltrexone hydrochloride
Trade Name:Trexonil™
Marketing Status:Prescription

 

II. INDICATIONS FOR USE

For use as an antagonist to carfentanil citrate immbolization in free-ranging or confined elk and moose (Cervidae).

 

III. DOSAGE FORM, ROUTE OF ADMINISTRATION AND RECOMMENDED DOSAGE:

The drug is supplied as a sterile solution containing 50 mg of naltrexone hydrochloride per mL in a 20 mL multiple dose vial. Naltrexone is to be administered with one fourth calculated dose (25%) given intravenously and three fourths (75%) calculated dose given subcutaneously. The recommended dosage is 100 mg of naltrexone hydrochloride per 1 mg of carfentanil citrate administered.

 

IV. EFFECTIVENESS

Due to the nature of the species in which the efficacy of naltrexone to reverse carfentanil was to be demonstrated, and humane concerns for the safety and welfare of these animals as well as the fact that these animals are wild and generally free-ranging, it was deemed inappropriate and inhumane to immobilize them with carfentanil citrate and leave them unreversed. Immobilization of elk and moose (cervids) without reversal puts them at risk to complications of bloat, regurgitation of rumen contents, aspiration of rumen contents into the lungs, and self-induced trauma as a result of incoordination during the natural recovery phases. Furthermore, published peer-reviewed scientific literature contains information documenting the recovery times following carfentanil citrate immobilization. Animals have been immobilized with carfentanil citrate up to three hours as discussed in published peer-reviewed literature(1). In accordance with 21 CFR 514.111(a)(5)(ii), the effectiveness of naltrexone HCl as an antagonist to carfentanil in elk and moose is conclusively established by the alternative procedure utilized in the clinical field trials.

LITERATURE CITED

(1)Mueleman, T., J.D. Port, T.H. Stanley and K.F. Williard. 1984. Immobilization of elk and moose with carfentanil. J. Wildl. Manage. 48(1):258-262.

A. PIVOTAL STUDY 1:

Following is a clinical dose titration study which demonstrated the efficacy of Trexonil™ in reversing the effects of carfentanil citrate in elk:

  1. Type of Study: Dose Titration and Acute Toxicity
  2. Name and Address of Investigator:

    Dr. Michael Miller and Dr. Margaret Wild
    Colorado Division of Wildlife
    317 W. Prospect
    Fort Collins, CO 80526

  3. General Design of Investigation:
    1. Purpose: To determine a minimum dose of naltrexone that will effectively reverse carfentanil immobilization of elk with no renarcotization.
    2. Test Animals:
      1. Species: Elk (Cervus elaphus)
      2. Number: 12
      3. Age: 1.3 to 6.3 years Sex: 4 castrated males and 8 females
    3. Type of Control: Each animal served as its own control as effects of naltrexone reversal of carfentanil immobilization are dramatic and self evident. A crossover design was used.
    4. Dosage Form: Sterile injection, 50 mg/mL
    5. Route of Administration: 1/4 intravenously and 3/4 subcutaneously
    6. Dosage:
      • Group A: 25 mg naltrexone hydrochloride/mg carfentanil administered following a 15 minute immobilization with carfentanil
      • Group B: 50 mg naltrexone hydrochloride/mg carfentanil administered following a 15 minute immobilization period with carfentanil
      • Group C: 100 mg naltrexone hydrochloride/mg carfentanil administered following a 15 minute immobilization period with carfentanil
      • Group D: 500 mg naltrexone hydrochloride/mg carfentanil administered following a 30 minute immobilization period with carfentanil

      Each animal received 3 of the 4 dosages.

    7. Parameters Measured:
      1. Body Weight (kg)
      2. Amount of Carfentanil Citrate Administered in mg
      3. Dose Rate of Carfentanil (mcg/kg)
      4. Amount of Naltrexone Hydrochloride Administered in mg
      5. Time to Standing With Full Mobility (Level 5) in Minutes
      6. Adverse Reactions (Renarcotization)
  4. Results: Response to administration of naltrexone hydrochloride following immobilization with 10 mcg/kg of carfentanil citrate via hand injection was determined in elk. Individuals were observed at one minute intervals for up to 16 minutes following injection of carfentanil, and levels of induction of immobilization recorded as follows:
    • Level 1 No effect
    • Level 2 Impaired gait, prancing gait, some excitement
    • Level 3 Lowered head, braced stance, hindquarter weakness
    • Level 4 Sternal recumbency
    • Level 5 Lateral recumbency

    Fifteen minutes following sternal recumbency, one of three dose levels of naltrexone hydrochloride was administered, and animals observed for one minute intervals for up to 16 minutes. One elk in Group B and one elk in Group C did not become fully immobilized. It is noted that in Group D 500 mg naltrexone (5X) was administered following 30 minutes of sternal recumbency, in order to document that they could not rise on their own. Reversal from the effects of carfentanil were assessed as follows:

    • Level 1 No effect
    • Level 2 Increased respiration, increased muscular control
    • Level 3 Able to hold head erect, maintains sternal recumbency
    • Level 4 Able to stand with control of legs, head, and braced stance
    • Level 5 Full mobility, normal attitude

    Additional observations were made at one hour, eight hours, twenty four hours, and daily for three days to identify evidence of renarcotization (lessened fear response to people, hypermetria, open-mouthed breathing, isolation from other elk, reluctance to move, and "star-gazing") or adverse reactions. The results among cases that were completely immobilized are summarized as follows:

    Ed. note: The following table has 5 columns.

    No. of AnimalsDose Group (mg)Induction Time
    (Average Time in Min.)
    Reversal Time
    (Average Time in Min.)
    Renarcotization Occurrence (%)
    9253.16.078
    8503.65.438
    81003.15.10
    95002.84.9*0

    *Naltrexone administration was given 30 minutes after carfentanil to support the concept that animals would not rise on their own.  Data accrued from the first 15 minute period provided control information.

    Four of nine animals in the 25 mg group reversed within five minutes. Three animals in that group reversed in six minutes. Four of eight animals in the 50 mg group reversed within five minutes, while three reversed in six minutes, and one in seven minutes. Seven of eight animals in the 100 mg group reversed within five minutes, and eight of nine elk in the 500 mg group reversed within that time. The longest time that an animal took to achieve Level 5 (full mobility, normal attitude) was ten minutes and occurred in an elk in the 25 mg group. One animal in both the 100 mg and 500 mg groups took nine minutes to reverse.

  5. Statistical Analysis: Using the proportions of animals reversed by five minutes in the control (see asterisk above), the 25 mg, the 50 mg, and the 100 mg naltrexone/mg carfentanil groups, a Cochran-Mantel-Haenszel test, stratifying by treatment period, yielded a significant test of nonzero correlation (p < 0.001). By increasing dose, the proportions were: 0/9, 4/9, 4/8, and 7/8. Since none of the control animals was reversed in 5 minutes, the biggest difference is between controls and treated animals; however, dropping the controls and testing again yields a test of nonzero correlation whose p valaue is less than 0.059. This indicates that there was a dose related increase in the proportion of animals reversed within five minutes.
  6. Conclusion: One hundred milligrams of naltrexone hydrochloride administered per mg of carfentanil citrate, when 1/4 of the dose is administered intravenously and 3/4 of the dose is administered subcutaneously, produced safe and effective reversal of carfentanil citrate in elk with no renarcotization. Doses of 50 mg and 25 mg per mg of carfentanil used resulted in clinically significant renarcotization in elk. Signs of renarcotization included open-mouth breathing, ataxia, and "starry-gazing." Elk which did not receive naltrexone at 15 minutes showed no evidence of recovery until the reversing agent was administered at 30 minutes. A 5X dose (500 mg naltrexone per mg carfentanil used) resulted in no adverse effects attributed to the drug in any animal in this study. One elk in group D (5X) was noted to be "very excited" and vocalizing one hour post naltrexone administration, but this was attributed to separation from her herd group. Furthermore, the administration of five times the recommended dose of naltrexone did not yield a clinically relevant reduction in reversal time. It was concluded that 100 mg of naltrexone hydrochloride per mg of carfentanil, when 1/4 of the dose is administered intravenously and 3/4 of the dose is administered subcutaneously, is safe and effective for reversal of carfentanil effects in cervids.
  7. Adverse Reactions: No adverse reactions occurred at the 1X dose and none that were attributabale to the 5X dose were noted. In the 1/2X and 1/4X dose groups, signs of mild renarcotization were observed including open-mouth breathing, ataxia, and "star-gazing." The animals were observed for three days.

B. PIVOTAL STUDY 2:

Following is a pivotal clinical field study which demonstrated the efficacy of Trexonil™ in reversing the effects of carfentanil citrate in elk.

  1. Type of Study: Field Efficacy
  2. Name and Address of Investigator:

    Dr. Richard Kinyon
    Conrad Veterinary Hospital
    307 North Main Street
    Conrad, MT 59425

  3. General Design of Investigation:
    1. Purpose: To demonstrate that naltrexone hydrochloride will effectively reverse carfentanil immobilization of elk under field conditions.
    2. Test Animals:
      1. Species: Elk (Cervus elaphus)
      2. Number: 16
      3. Age: 2-7 years Sex: male
    3. Type of Control: Each animal served as its own control as effects of naltrexone reversal of carfentanil immobilization are dramatic and self evident.
    4. Dosage Form: Sterile injection, 50 mg/mL
    5. Route of Administration: 1/4 intravenously and 3/4 subcutaneously
    6. Dosage: 100 mg naltrexone hydrochloride/mg carfentanil used
    7. Parameters Measured:
      1. Body Weight (kg)
      2. Amount of Carfentanil Citrate Administered in mg
      3. Dose Rate of Carfentanil (mcg/kg)
      4. Amount of Naltrexone Hydrochloride Administered in mg
      5. Time to Standing With Full Mobility (Level 5) in Minutes
      6. Adverse Reactions (Renarcotization)
  4. Results: All elk immobilized in this study were fully reversed from the effects of carfentanil within four minutes of naltrexone administration. The data collected provide information on reversal of carfentanil in free-ranging elk immobilized from helicopters:

    Ed. note: The following table has 6 columns.

    No. of AnimalsWt (Ave kg)Carf (Ave mg)Ave Carf Dose Rate (mcg/kg)Naltx (Ave mg)Ave Time to Level 5 Reversal (min)
    16289.02.9610.32973.4
  5. Conclusion: One hundred milligrams of naltrexone hydrochloride administered per mg of carfentanil citrate, when 1/4 of the dose was administered intravenously and 3/4 of the dose was administered subcutaneously, produced effective reversal of immobilization in free-ranging elk with no evidence of renarcotization.
  6. Adverse Reactions: No adverse reactions were encountered during this study.

C. PIVOTAL STUDY 3:

Following is a pivotal clinical field study which demonstrated the efficacy of Trexonil™ in reversing the effects of carfentanil citrate in elk.

  1. Type of Study: Field Efficacy
  2. Name and Address of Investigator:

    Dr. Sherman J. Smith
    Three Forks Veterinary Hospital
    223 Railroad Avenue
    Three Forks, MT 59752

  3. General Design of Investigation
    1. Purpose: To demonstrate the efficacy of naltrexone hydrochloride to reverse carfentanil immobilization in elk under field conditions.
    2. Test Animals:
      1. Species: Elk (Cervus elaphus)
      2. Number: 72
      3. Age: 1 to 8 years Sex: male
    3. Type of Control: Each animal served as its own control as effects of naltrexone reversal of carfentanil immobilization are dramatic and self evident.
    4. Dosage Form: Sterile injection, 50 mg/mL
    5. Route of Administration: 1/4 intravenously and 3/4 subcutaneously
    6. Dosage: 100 mg naltrexone hydrochloride/mg carfentanil used
    7. Parameters Measured:
      1. Body Weight (kg)
      2. Amount of Carfentanil Citrate Administered in mg
      3. Dose Rate of Carfentanil (mcg/kg)
      4. Amount of Naltrexone Hydrochloride Administered in mg
      5. Time to Standing With Full Mobility (Level 5) in Minutes
      6. Adverse Reactions (Renarcotization)
  4. Results: All animals immobilized by carfentanil citrate were administered naltrexone at the ratio of approximately 100 mg naltrexone per mg carfentanil. One fourth of the dose was administered intravenously and three fourths was administered subcutaneously.

    The following provides a summary of the average of results:

    Ed. note: The following table has 6 columns.

    No. of AnimalsWt (Ave kg)Carf (Ave mg)Ave Carf Dose Rate (mcg/kg)Naltx (Ave mg)Ave Time to Level 5 Reversal (min)
    72285.72.910.5293.85.1
    Seventy two male elk were effectively immobilized. The average time to reach level 5 of reversal occurred in 5 minutes, with twenty four animals not reversing to level 5 within five minutes. However, only four animals took greater than ten minutes to achieve level 5. The longest time to reversal to level 5 was eleven minutes. The time to reversal to level 5 was not recorded for one animal because this animal wandered out of sight before Level 5 could be further observed by the investigator.
  5. Conclusions: One hundred milligrams of naltrexone hydrochloride administered per mg of carfentanil citrate, when 1/4 of the dose was administered intravenously and 3/4 of the dose was administered subcutaneously, produced effective reversal of immobilization in free-ranging elk with no evidence of renarcotization.
  6. Adverse Reactions: No adverse reactions were noted during this study.

D. PIVOTAL STUDY 4:

Following is a pivotal clinical field study which demonstrated efficacy of Trexonil™ in reversing carfentanil citrate in moose.

  1. Type of Study: Field Efficacy
  2. Name and Address of Investigator:

    Dr. Richard Kinyon
    Conrad Veterinary Hospital
    307 North Main Street
    Conrad, MT 59425

  3. General Design of Investigation:
    1. Purpose: To demonstrate the efficacy of naltrexone hydrochloride to reverse carfentanil immobilization in moose under field conditions.
    2. Test Animals:
      1. Species: Moose (Alces alces) Number: 29
      2. Age: adult and yearling Sex: 9 male and 20 female
    3. Type of Control: Each animal served as its own control as effects of naltrexone reversal of carfentanil immobilization are dramatic and self evident.
    4. Dosage Form: Sterile injection, 50 mg/mL
    5. Route of Administration: 1/4 intravenously and 3/4 subcutaneously
    6. Dosage: 100 mg naltrexone hydrochloride/mg carfentanil used
    7. Parameters Measured:
      1. Body Weight (kg)
      2. Amount of Carfentanil Citrate Administered in mg
      3. Dose Rate of Carfentanil (mcg/kg)
      4. Amount of Naltrexone Hydrochloride Administered in mg
      5. Time to Standing With Full Mobility (Level 5) in Minutes
      6. Adverse Reactions (Renarcotization)
  4. Results: Twenty seven of twenty nine animals in this study immobilized with carfentanil from aerial darting were observed to reach reversal stage 5 (full mobility, normal attitude) within 5 minutes following naltrexone administration. Two animals were reversed to Level 4 (able to stand with control of legs, head, and braced stance) within five minutes and wandered out of the investigator's sight before Level 5 could be documented. Only one moose for which Level 5 of reversal was recorded failed to attain it within five minutes (she took six minutes). The following results were reported:

    Ed. note: The following table has 6 columns.

    No. of AnimalsWt (Ave kg)Carf (Ave mg)Ave Carf Dose Rate (mcg/kg)Naltx (Ave mg)Ave Time to Level 5 Reversal (min)
    294873.98.04004.4
  5. Conclusion: One hundred milligrams of naltrexone hydrochloride administered per mg of carfentanil citrate, when 1/4 of the dose was administered intravenously and 3/4 of the dose was administered subcutaneously, produced effective reversal of immobilization in free-ranging moose with no evidence of renarcotization.
  6. Adverse Reactions: No adverse reactions were encountered during this study.

E. SUPPORTIVE STUDY 1:

Following is a supportive clinical field study which demonstrates efficacy and safety of Trexonil™ in reversing carfentanil citrate in elk.

  1. Type of Study: Field Efficacy
  2. Name and Address of Investigator:

    Dr. Little Liedblad
    Deschutes Veterinary Clinic
    1474 NW Hill Street
    Bend, OR 97701

  3. General Design of Investigation:
    1. Purpose: To demonstrate that 100 mg of naltrexone hydrochloride per mg carfentanil citrate used effectively reverses carfentanil immobilization of elk.
    2. Test Animals:
      1. Species: Elk (Cervus canadensis) Number: 22
      2. Age: Approx. 1.5 years Sex: female
    3. Type of Control: Each animal served as its own control as effects of naltrexone reversal of carfentanil immobilization are dramatic and self evident.
    4. Dosage Form: Sterile injection, 50 mg/mL
    5. Route of Administration: 1/4 intravenously and 3/4 subcutaneously
    6. Dosage: 100 mg naltrexone hydrochloride/mg carfentanil used
    7. Parameters Measured:
      1. Body Weight (kg)
      2. Amount of Carfentanil Citrate Administered in mg
      3. Dose Rate of Carfentanil (mcg/kg)
      4. Amount of Naltrexone Hydrochloride Administered in mg
      5. Time to Standing With Full Mobility (Level 5) in Minutes
      6. Adverse Reactions (Renarcotization)
  4. Results: Twenty two elk were immobilized during this study. Eleven animals took longer than five minutes to achieve full mobility. The longest time was eleven minutes. The following results were reported:

    Ed. note: The following table has 6 columns.

    No. of AnimalsWt (Ave kg)Ave Carf Dose (mg)Ave Carf Dose Rate (mcg/kg)Naltx (Ave mg)Ave Time to Level 5 Reversal (min)
    22136.51.39.81346.1
  5. Conclusion: One hundred milligrams of naltrexone hydrochloride administered per mg of carfentanil citrate, when 1/4 of the dose was administered intravenously and 3/4 of the dose was administered subcutaneously, produced effective reversal of immobilization in free-ranging elk with no evidence of renarcotization.
  6. Adverse Reactions: No adverse reactions were encountered during this study.

F. SUPPORTIVE STUDY 2:

The following is a supportive field efficacy study which demonstrated the efficacy of Trexonil™ in reversing carfentanil citrate in moose:

  1. Type of Study: Field Efficacy
  2. Name and Address of Investigator:

    Dr. Stephen Kerr
    Colorado State University
    Veterinary Teaching Hospital
    Ft. Collins, CO 80523

  3. General Design of Investigation:
    1. Purpose: To demonstrate that naltrexone hydrochloride at 100 mg per mg carfentanil citrate used, administered 1/4 intravenously and 3/4 subcutaneously effectively reverses carfentanil immobilization of moose under field conditions.
    2. Test Animals:
      1. Species: Moose (Alces alces)
      2. Number: 14
      3. Age: calves, yearling and adults Sex: 6 male and 8 female
    3. Type of Control: Each animal served as its own control as effects of naltrexone reversal of carfentanil immobilization are dramatic and self evident.
    4. Dosage Form: Sterile injection (50 mg/mL)
    5. Route of Administration: 1/4 intravenously and 3/4 subcutaneously
    6. Dosage: 100 mg naltrexone hydrochloride/mg carfentanil used
    7. Parameters Measured:
      1. Body Weight (kg)
      2. Amount of Carfentanil Citrate Administered in mg
      3. Dose Rate of Carfentanil (mcg/kg)
      4. Amount of Naltrexone Hydrochloride Administered in mg
      5. Time to Standing With Full Mobility (Level 5) in Minutes
      6. Adverse Reactions (Renarcotization)
  4. Results: Fourteen moose darted from vehicles or personnel on the ground were immobilized with carfentanil. The range of time to Level 5 reversal (full mobility) was from 3 to 14 minutes. The following results were provided:

    Ed. note: The following table has 6 columns.

    No. of AnimalsAve Wt (kg)Ave Carf Dose (mg)Ave Carf Dose Rate (mcg/kg)Ave Naltx Dose (Ave mg)Ave Time to Level 5 Reversal (min)
    14328.62.99.5289.38.8
  5. Conclusion: One hundred milligrams of naltrexone hydrochloride administered per mg of carfentanil citrate, when 1/4 of the dose was administered intravenously and 3/4 of the dose was administered subcutaneously, produced effective reversal of immobilization in free-ranging moose.
  6. Adverse Reactions: Adverse effects noted during this study included hiccupping, respiratory distress (due to positioning), hyperthermia, and slipping to a deeper plane of immobilization following administration of naltrexone resulting in partial reversal of the effects of carfentanil.

 

V. ANIMAL SAFETY

Conventional safety studies were not conducted with naltrexone HCl due to the nature of the target species. These animals are generally not confined and are governed by state or federal entities; therefore, classic pre-clinical laboratory toxicity studies were not conducted. Nevertheless, the studies which were conducted demonstrate that the drug, when used at five times the recommended dose or used multiple times in a single animal, did not result in clinically relevant signs of renarcotization, other adverse reactions, or side effects which could necessarily be attributed to the drug.

The rationale for developing the drug for use in elk and moose (cervidae) is based on the fact that if left in a position of prolonged lateral recumbency following immobilization, these animals would be susceptible to bloat and/or aspiration pneumonia. The use of naltrexone HCl provides assurance that the effects of carfentanil will be safely reversed so that these animals can be returned to their natural environment.

A. PIVOTAL STUDY 1:

To demonstrate the safety of naltrexone hydrochloride.

  1. Type of Study: Acute toxicity
  2. Name of Investigator:

    Dr. Michael Miller and Dr. Margaret Wild
    Colorado Division of Wildlife
    Wildlife Research Center
    Fort Collins, CO 80526

See Pivotal Efficacy Study #1 (pages 1-5), which addresses use of a 5X dose of the drug in elk.

B. PIVOTAL STUDY 2:

Following is a pivotal clinical field study which demonstrated the safety of Trexonil™ in reversing the effects of carfentanil citrate in 6 month old, female elk.

  1. Type of Study: Field Safety
  2. Name and Address of Investigator:

    Dr. Terrence McCoy
    National Forest Land
    La Grande, Oregon

  3. General Design of Investigation:
    1. Purpose: To demonstrate that naltrexone hydrochloride will safely reverse carfentanil immobilization of young elk under field conditions.
    2. Test Animals:
      1. Species: Elk (Cervus elaphus)
      2. Number: 35
      3. Age: 6 months Sex: Female
    3. Type of Control: Each animal served as its own control as effects of naltrexone reversal of carfentanil immobilization are dramatic and self evident.
    4. Dosage Form: Sterile injection, 50 mg/mL
    5. Route of Administration: 1/4 intravenously and 3/4 subcutaneously
    6. Dosage: 100 mg naltrexone hydrochloride/mg carfentanil used
    7. Parameters Measured:
      1. Body Weight (kg)
      2. Amount of Carfentanil Citrate Administered in mg
      3. Dose Rate of Carfentanil (mcg/kg)
      4. Amount of Naltrexone Hydrochloride Administered in mg
      5. Time to Standing With Full Mobility (Level 5) in Minutes
      6. Adverse Reactions
  4. Results: The following summarizes the results:

    Ed. note:The following table has 6 columns.

    No. of AnimalsAve Wt (kg)Carf (Ave mg)Ave Carf Dose Rate (mcg/kg)Naltx (Ave mg)Ave Time to Level 5 Reversal (min)
    3574.50.741074.35.7
  5. Conclusion: The data generated substantiate the safety of naltrexone hydrochloride administered to reverse carfentanil immobilization in free-ranging sub-adult elk under field conditions at 100 mg/mg of carfentanil used.
  6. Adverse Reactions: No adverse reactions were encountered during this study.

C. SUPPORTIVE STUDY 1:

Following is a supportive field study which demonstrated the safety of Trexonil™ in reversing carfentanil citrate in elk:

  1. Type of Study: Field Safety
  2. Name and Address of Investigator:

    Dr. Jack Mortenson
    Wildlife Safari
    Safari Rd.
    Winston, OR 97496

  3. General Design of Investigation:
    1. Purpose: To demonstrate that naltrexone hydrochloride at 100 mg per mg carfentanil citrate used, administered 1/4 intravenously and 3/4 subcutaneously safely reverses carfentanil immobilization of elk that were immobilized under field conditions.
    2. Test Animals:
      1. Species: Elk (Cervus elaphus)
      2. Number: 4
      3. Age: 3 to 7 years Sex: 3 male and 1 female
    3. Type of Control: Each animal served as its own control as effects of naltrexone reversal of carfentanil immobilization are dramatic and self evident.
    4. Dosage Form: Sterile injection, 50 mg/mL
    5. Route of Administration: 1/4 intravenously and 3/4 subcutaneously
    6. Dosage: 100 mg naltrexone hydrochloride/mg carfentanil used
    7. Parameters Measured:
      1. Body Weight (kg)
      2. Amount of Carfentanil Citrate Administered in mg
      3. Dose Rate of Carfentanil (mcg/kg)
      4. Amount of Naltrexone Hydrochloride Administered in mg
      5. Time to Standing With Full Mobility (Level 5) in Minutes
      6. Adverse Reactions (Renarcotization)
  4. Results: All four animals were adequately immobilized and reversed in this study. Three of the four animals were immobilized twice in a three day period. The average reversal to full mobility occurred in 6.7 minutes. Only two of the immobilization episodes resulted in reversal by five minutes; however, six of seven episodes resulted in reversal by seven minutes. On one occasion the elk took 14 minutes to fully reverse. The following table summarizes results of this study:

    Ed. note: The following table has 7 columns.

    No. of AnimalsNo. of Immob.Wt (Ave kg)Carf (Ave mg)Ave Carf Dose Rate (mcg/kg)Naltx (Ave mg)Ave Time to Level 5 Reversal (min)
    473703.810.33806.7
  5. Conclusion: The data support the safety of naltrexone when used multiple times in the same animal when administered at the recommended dose of 100 mg naltrexone per mg carfentanil used.
  6. Adverse Reactions: No adverse reactions were encountered during this study.

D. SUPPORTIVE STUDY 2:

Following is a supportive clinical field study which demonstrated the safety of Trexonil™ in reversing the effects of carfentanil citrate in moose.

  1. Type of Study: Field Safety
  2. Name and Address of Investigator:

    Dr. William Taylor
    Alaska Fish & Game
    333 Raspberry Road
    Anchorage, AK 99518-1599

  3. General Design of Investigation:
    1. Purpose: To demonstrate that naltrexone hydrochloride will safely reverse carfentanil immobilization of moose.
    2. Test Animals:
      1. Species: Moose (Alces alces)
      2. Number: 5
      3. Age: 1.4 years Sex: male
    3. Type of Control: Each animal served as its own control as effects of naltrexone reversal of carfentanil immobilization are dramatic and self evident.
    4. Dosage Form: Sterile injection, 50 mg/mL
    5. Route of Administration: 1/4 intravenously and 3/4 subcutaneously
    6. Dosage: 100 mg naltrexone hydrochloride/mg carfentanil used
    7. Parameters Measured:
      1. Body Weight (kg)
      2. Amount of Carfentanil Citrate Administered in mg
      3. Dose Rate of Carfentanil (mcg/kg)
      4. Amount of Naltrexone Hydrochloride Administered in mg
      5. Time to Standing With Full Mobility (Level 5) in Minutes
      6. Adverse Reactions (Renarcotization)
  4. Results: Five moose were immobilized two to four times each over an eight day period with carfentanil citrate and reversed with the appropriate dose of naltrexone hydrochloride for a total of eighteen immobilization episodes. These animals also received 50-150 mg xylazine at the time of carfentanil administration. In one episode, the animal was reversed to Level 4 (able to stand with control of legs and head, and braced stance) within six minutes and wandered out of the investigator's sight before Level 5 (full mobility) could be documented. All other immobilization episodes resulted in full reversal within nine minutes, although only one episode resulted in full reversal by five minutes. Recovery times to full reversal following the last immobilization episode were comparable to those noted in the first episode. The following is a summary of results:

    Ed. note: The following table has 7 columns.

    No. of AnimalsNo. of Immob.Wt (Ave kg)Carf (Ave mg)Ave Carf Dose Rate (mcg/kg)Naltx (Ave mg)Ave Time to Level 5 Reversal (min)
    518335.33.09300.07.1
  5. Conclusion: This study demonstrated that repeated dosing of naltrexone at 100 mg/mg of carfentanil citrate used is safe in moose. It also provides information on concurrent use of an additional drug for sedation/immobilization (xylazine) with no apparent signs of interference.
  6. Adverse Reactions: No adverse reactions were encountered during this study.

VI. HUMAN FOOD SAFETY:

A. Human Food Safety

Data on human safety, pertaining to consumption of drug residues in food, were not required for approval of the NADA. This product is labeled as a prescription drug not for use in domestic animals or animals to be consumed for food. Use of this drug is also prohibited 45 days before or during a legal hunting season in free-ranging animals.

B. Human Safety Considerations other than Food Safety

Labeling contains adequate caution statements.

 

VII. AGENCY CONCLUSIONS:

The data submitted in support of this NADA comply with the requirements of Section 512 of the Act and Part 514 of the implementing regulations. The data demonstrated that Trexonil (naltrexone hydrochloride) injection when used under the labeled conditions of use is safe and effective.

Trexonil is restricted to use by or on the order of a licensed veterinarian because professional expertise is required to determine when an elk or moose should be reversed from the immobilizing effects of the prescription drug, carfentanil citrate.

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.

 

VIII. LABELING (Attached)

  1. Package insert
  2. Box label
  3. Vial label

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