Current Understanding of Analgesic Efficacy and Associated Side Effects in Reptiles
While our current understanding of pain and analgesia in reptiles is somewhat limited, data from our laboratory support the following conclusions:
1. Several reptile species respond consistently to application of a noxious thermal stimulus by withdrawing a hindlimb or tail.1,2
2. Mu-opioid receptor agonists (e.g., morphine) provide analgesia in red-eared slider turtles and bearded dragons, while kappa- (e.g., butorphanol) and delta-opioid receptor agonists do not.1,2 However, both morphine and butorphanol cause moderate to marked respiratory depression in red-eared slider turtles.1
3. Corn snakes were variable in their responses to noxious thermal stimuli, but did demonstrate an increased latency to tail withdrawal after a high dosage of butorphanol was administered.2
Studies involving opioid analgesic efficacy and respiratory side effect are ongoing in our laboratory. The objectives are to 1) determine the effects of multiple analgesic drugs on nociceptive behaviors in adult, red-eared slider turtles (Trachemys scripta), using a thermal hind limb withdrawal latency test; and 2) evaluate effects of these same analgesic drugs on respiration. Infrared heat stimuli were applied to the plantar surface of turtle hindlimbs, and thermal withdrawal latencies were measured before and after subcutaneous administration of physiologic saline, buprenorphine (1.0 mg/kg), tramadol (10 and 25 mg/kg), meperidine (50 mg/kg), and methadone (1.0, 3.0 and 5.0 mg/kg). Thermal withdrawal latencies following drug administration were similar in turtles receiving saline or buprenorphine. However, hind limb thermal withdrawal latencies increased in turtles after administration of tramadol, methadone, and meperidine. All of these analgesic drugs caused respiratory depression.
Supported by grants from the Morris Animal Foundation, American College of Laboratory Animal Medicine Foundation, and National Science Foundation (IOB-51580).
1. Sladky, K.K., V. Miletic, J. Paul-Murphy, M. Kinney, R. Dallwig, and S.M. Johnson. 2007. Analgesic efficacy and respiratory effects of butorphanol and morphine in turtles (Trachemys scripta). J. Am. Vet. Med. Assoc. 230(9):1356–1362.
2. Sladky, K.K., M. Kinney, and S.M. Johnson. Analgesic efficacy of butorphanol and morphine in bearded dragons (Pogona vitticeps) and corn snakes (Elaphe guttata). J. Am. Vet. Med. Assoc. (in press).