Evaluation of the thermal antinociceptive effects of subcutaneous administration of butorphanol tartrate or butorphanol tartrate in a sustained-release poloxamer 407 gel formulation to orange-winged Amazon parrots (Amazona amazonica)

OBJECTIVE

To determine the thermal antinociceptive effects of butorphanol tartrate and butorphanol tartrate in a sustained-release 25% poloxamer 407 (P407) gel formulation (But-P407) in parrots.

ANIMALS

13 orange-winged Amazon parrots (Amazona amazonica).

PROCEDURES

First, butorphanol tartrate (5 mg/kg) or saline (0.9% NaCl) solution was administered IM to birds in a randomized complete crossover design. The temperature prompting a foot withdrawal response to a thermal stimulus (ie, the thermal threshold) was determined 30 minutes before (baseline) and at various points after treatment administration. Second, But-P407 (12.5 mg/kg) or P407 was administered SC in a similar crossover design. Thermal threshold was determined before and at various points after treatment administration. Third, But-P407 (12.5 mg/kg) or saline solution was administered SC and evaluated as in the second trial. Sedation was scored immediately before each time point in all 3 trials.

RESULTS

In the first trial, a significant increase in thermal threshold was noted 30 minutes after butorphanol tartrate (vs saline solution) administration. No sedation was noted. In the second and third trials, no significant difference was identified between results for But-P407 and those for either control treatment (saline solution or P407). Mild sedation was noted in the second trial following But-P407 administration.

CONCLUSIONS AND CLINICAL RELEVANCE

Results suggested a small but significant thermal antinociceptive effect of butorphanol tartrate lasting between 30 minutes and 1.5 hours in orange-winged Amazon parrots. No antinociceptive effect of butorphanol tartrate was demonstrated when delivered in P407. Further research is needed to evaluate the potential analgesic effects of But-P407.

Advances in Therapeutics and Delayed Drug Release

Reducing the frequency of drug administration in the treatment of exotic pets is advantageous because it may decrease handling frequency and thus potential stress and injury risk for the animal, increase owner compliance with the prescribed treatment, and decrease need for general anesthesia in patients that cannot be handled safely. Increasing efficient drug plasma concentration using sustained-released delivery systems is an appealing solution. Potential candidates that could provide a promising solution have been investigated in exotic pets. In this article, the technologies that are the closest to being integrated in exotic pet medicine are reviewed: osmotic pumps, nanoparticles, and hydrogels.

Sustained-Release Injectable Hydrogel Formulations for Administration of Sodium Salicylate in Broiler Chickens

We developed injectable hydrogels for the slow release of analgesic drugs in birds as an in vivo model of pharmacokinetics in wild avian species. Hydrogels loaded with sodium salicylate (NaSA) were injected subcutaneously in Ross broiler chickens. The hydrogels were made by dissolving sodium alginate and NaSA in water at 2 different concentrations (low, LALG; high, HALG) and then adding calcium chloride. In vitro drug release studies were performed by swelling the hydrogels in water and analyzing serial samples by ultraviolet-visible (UV-Vis) spectroscopy. Dried hydrogel films of the same formulations of the two alginate concentrations then were dissolved in sterile water for the in vivo pharmacokinetic study conducted in 18 chickens divided into 3 groups of 6 birds. Each of the 2 resultant NaSA hydrogel solutions were filtered with 0.2-µm syringe filters before injecting at a NaSA dose of 150 mg/kg SC in the respective LALG or HALG groups. The control group was injected SC with the same dose of NaSA dissolved in water. Pharmacokinetics parameters calculated by the compartmental and noncompartmental approaches were compared among the 3 groups by the Kruskal-Wallis test. Results of in vitro studies showed that both hydrogels released 80% of the drug during the first 3.5 hours. Results of the pharmacokinetic study indicated that NaSA concentrations remained above the minimum effective concentration (MEC) for analgesia in humans for 24 ± 8.9 (LALG) to 26 ± 4 (HALG) hours for the hydrogel formulations compared to 10 ± 5.6 hours for the aqueous formulation. These hydrogel formulations may have potential in providing long-term analgesia in avian species, but need further evaluation with pharmacodynamic or pharmacokinetic/pharmacodynamic modeling studies.

Compounding and Extralabel Use of Drugs in Exotic Animal Medicine

Extralabel drug use is the use of a Food and Drug Administration (FDA)-approved drug in a manner different from what is stipulated on the approved label. Compounding is the process of preparing a medication in a manner not indicated on the label to create a formulation specifically tailored to the needs of an individual patient. Extralabel drug use and compounding are vital aspects of safe and effective drug delivery to patients in exotic animal practice. There are few FDA-approved drugs for exotic animal species, and many approved drugs for other species are not available in suitable formulations for use in exotic animals.

Pharmacokinetics of butorphanol tartrate in a long-acting poloxamer 407 gel formulation administered to Hispaniolan Amazon parrots (Amazona ventralis)

OBJECTIVE To determine pharmacokinetics of butorphanol tartrate incorporated into poloxamer 407 (P407) after SC administration to Hispaniolan Amazon parrots (Amazona ventralis). ANIMALS 11 adult Hispaniolan Amazon parrots (6 males and 5 females; 11 to 27 years old). PROCEDURES A sterile formulation of butorphanol in P407 (But-P407) 25% (percentage determined as [weight of P407/weight of diluent] × 100]) was created (8.3 mg/mL). Five preliminary experiments (2 birds/experiment) were performed to determine the ideal dose for this species. The formulation then was administered (12.5 mg/kg, SC) to 8 birds. Blood samples were collected before (time 0) and 0.08, 0.5, 1, 2, 4, 8, 12, and 24 hours after drug administration. Some birds were used more than once, with a washout period of ≥ 3 months between subsequent treatments. Butorphanol concentrations were quantitated by use of liquid chromatography-tandem mass spectrometry. Pharmacokinetic analysis was performed by use of noncompartmental analysis. RESULTS Maximal plasma butorphanol concentration was reached at 1.31 hours. Plasma concentrations of butorphanol remained > 100 ng/mL for > 3 hours (all birds) or > 4 hours (5/8 birds) but < 8 hours (all birds). Half-life of the terminal slope was 3.41 hours. No adverse effects were detected. CONCLUSIONS AND CLINICAL RELEVANCE Butorphanol was absorbed well from the But-P407 25% by Hispaniolan Amazon parrots, and absorption followed a pharmacokinetic profile compatible with a sustained-release drug. A dose of 12.5 mg/kg, SC, would theoretically provide analgesia for 4 to 8 hours. No adverse effects were detected. Studies on the pharmacodynamics of this formulation are necessary to confirm the degree and duration of analgesia.