Sedative and Cardiopulmonary Effects of Medetomidine and Atipamezole in American Alligators (Alligator mississippiensis)
J.A. Smith1, DVM, DACVA; M.A. Mitchell1, DVM, MS; K.A. Backues2, DVM; T.N. Tully1, DVM, MS; R.F. Aguilar2, DVM
The American alligator (Alligator mississipiensis) is an important species in both captive and wild environments where it may become necessary to capture and restrain for physical examination, medical treatment, ecologic research, or translocation. Most alligator handling requires some degree of manual restraint with or without sedation, which may result in dangerous contact for both the handler and alligator.
Historically, anesthetic agents in alligators have produced little or no effect, unpredictable recoveries or death.1 Increased contact with these animals has created a need for a sedative agent that is safe, easy to administer, provides adequate analgesia, and produces a rapid recovery. Alpha2 agonists provide sedation, analgesia and muscle relaxation. Antagonists are available to reverse these effects. The alpha2-agonist, medetomidine, has recently been approved for use in the United States, along with its specific reversal agent, atipamezole. This project was designed to evaluate the sedative and cardiopulmonary effects of both of these agents in an effort to identify a safe and effective sedative for alligators that can be reversed at the end of the procedure.
Fourteen farm-raised American alligators, averaging 114 cm (snout-vent length), were used in this study. An initial physical examination was performed under manual restraint and baseline data collected, including heart rate (HR), respiratory rate (RR), and cloacal temperature (T). Environmental temperatures were recorded throughout the day. Following collection of baseline data, each alligator received 0.15 mg/kg medetomidine (Domitor®, 1 mg/ml, Pfizer Animal Health, New York, NY, USA) IM in the left anconeus muscle, followed in 30 minutes by atipamezole (in a volume equal to the medetomidine; Antisedan®, 5 mg/ml, Pfizer Animal Health, New York, NY, USA) in the right anconeus muscle using a 22-g, 2.5 cm needle. Time to relaxation, resistance to handling, and loss of righting reflex were recorded as indicators of sedation. Ocular reflexes were recorded to assess depth of sedation and analgesia was assessed by absence of withdrawal reflex. Heart and respiratory rates were recorded at 5, 10, 15 and 30 minutes after medetomidine and at 5 and 15 minutes after atipamezole. Heart rate was determined by doppler ultrasound with the probe placed on the ventral midline just caudal to the pectoral girdle. Respiratory rate was determined by observation of thoracoabdominal excursions.
Three blood samples (2 ml each) were collected from the ventral tail vein of each alligator. A baseline sample, prior to any drug administration, and samples 15 minutes after medetomidine and atipamizole administration were collected. Packed cell volume (PCV), total protein (TP), partial pressures of CO2 (PCO2), and O2 (PO2), bicarbonate (HCO3), oxygen saturation and blood pH were evaluated.
Heart rate, respiratory rate, packed cell volume, total protein, PCO2, PO2, HCO3, oxygen saturation and blood pH were evaluated over time using Friedman’s nonparametric analysis of repeated data. A significant difference was determined at p<0.05. Where differences were apparent, Rhyne and Steels method for comparison of related samples to a control (time 0) was used with an experimental-wise error of alpha =0.05.
There was a significant difference in heart rate (p=0.001) and respiratory rate (p=0.001) over time. Comparisons between time periods and baseline showed a significant decrease in heart and respiratory rates at times 5 and 30 minutes after medetomidine and a return of heart rate to baseline at 5 and 15 minutes after atipamezole administration. HCO3 also showed a significant decrease after administration of medetomidine (15 minutes) with a return to baseline after atipamezole (15 minutes). Other blood parameters, including PCV (p=0.02), PCO2 (p=0.027), oxygen saturation (p=0.006) and blood pH (p=0.001), showed a significant decrease from baseline after medetomidine but did not return to baseline after atipamezole administration. Although these parameters were statistically different, there appeared to be no clinical significance.
Sedation was recorded in all 14 alligators. The loss of the righting reflex was also recorded in all test subjects, although the time to righting loss was variable. As for safety and reversibility, all 14 animals recovered rapidly and uneventfully. Further evaluation of these drugs in different size alligators and other crocodilians needs to be undertaken to evaluate their overall effectiveness.
The authors wish to thank Mr. Frank Ellender of Louisiana Land and Exploration Company for his time and assistance.
1. Jacobsen, E.R. 1984. Immobilization, blood sampling, necropsy techniques and diseases of crocodilians: A review. J. Zoo Anim. Med. 15:38–45.