Reptile Analgesia Without Respiratory Depression

In collaboration with Dr. Kurt Sladky (Surgical Sciences, UW School of Vet Med), our goal is to develop pharmacological approaches for providing pain relief (analgesia) in reptiles with minimal respiratory depression. Although turtles, lizards, and snakes are often kept as pets or in zoos, very little is known about pain relief in these species. To test for analgesic effects, noxious thermal (heat!) stimuli are applied to the hindlimbs of awake turtles or lizards (tail in snakes) before and after drug administration. Our major findings are that:

(1) Butorphanol (most widely prescribed drug for pain relief in reptiles) does not provide analgesia in red-eared slider turtles, while morphine provides analgesia and causes severe respiratory depression (Sladky et al, 2007).

(2) Morphine (but not butorphanol) provides analgesia in lizards (bearded dragons), while butorphanol (but not morphine at extremely high dosages!) provides analgesia in snakes (corn snakes) (Sladky et al, 2008).

(3) In awake turtles, drugs that activate mu-opioid receptors or delta-opioid receptors (to some extent) provide analgesia (Sladky et al, 2009). Unfortunately, mu-opioid receptor activation also causes profound respiratory depression in freely-swimming turtles (Johnson et al, 2008).

(4) Tramadol, an opioid drug that also alters brain serotonin and norepinephrine levels, provides long-lasting (>24 hours) analgesia with no respiratory depression at 5.0 mg/kg (Cummings et al, JAVMA, in press).

Thus, analgesic drug efficacy needs to be tested in all vertebrate species using appropriate techniques. One drug that works very well in one species (morphine, turtles) may have absolutely no analgesic effects in another species (morphine, snakes). Analgesia without significant respiratory depression may be achieved in turtles by using drugs with complex effects on brain function, such as tramadol. Future experiments are required to test whether tramadol is effective in other reptiles, such as snakes and lizards.

Dr. Kurt Sladky
Surgical Sciences Dept.
School of Veterinary Medicine