Introduction

Treating pain in animals is a fundamental part of what veterinarians do. The idea of addressing pain in reptile patients has only recently been discussed. Although there are a lot of anecdotal reports for treating pain in reptiles, in fact only a few actual studies have been performed. Before any attempt is made to determine the best way to treat pain in reptiles, it is imperative that we learn to recognize pain.

Understanding Pain in Reptiles

We have to assume that reptiles feel pain. But how? There have been studies looking at receptor sites. Reptiles have the same neurologic and receptor sites as do mammals, but clinically they don't seem to show similar responses. Why does the snake allow the mouse or rat to bite and not respond? Why does the iguana fall asleep under a heat lamp and suffer a third degree burn, only to wake, walk away and go and eat?

There are established pain scales for mammals, but there are no similar objective standards for evaluating pain in reptiles. Many of the signs that we associate with pain can also be attributed to other causes; for example, anorexia--common in mammals with pain--can also be caused in reptiles by something as simple as hypothermia.

In a survey by Matt Read members of the Association of Reptilian and Amphibian Veterinarians were asked if they felt that reptiles felt pain. 98.4% responded yes. In addition, they were asked how many used pain medications--surprisingly, only 39.5% of the respondents said that they used analgesics in their reptile patients. When asked what was the most common analgesic that they used, the answer was butorphanol.

Analgesia Studies in Reptiles

Greenacre et al. evaluated the effects of opioids in the Green Iguana. 5 animals were administered electrical shocks but were pre-treated with either butorphanol, buprenorphine or morphine. There were differences noted between control (saline) groups and animals receiving 1.5 and 8.0 mg/kg of butorphanol, but not for 0.4 or 4.0 mg/kg.

There were no differences noted between saline groups and those given buprenorphine.

Morphine pre-treated animals showed a depressed response to the shock at 1.0 mg/kg, but not at 0.4 or 2.0 mg/kg.

Sladky et al. looked at the antinociceptive and respiratory effects of butorphanol and morphine in three reptile species (Red-eared Sliders, Bearded Dragons and Corn Snakes). The subjects were pretreated with either butorphanol (a kappa agonist) or morphine (a mu agonist). Each subject was then subjected to an infrared heat stimulus and the response was measured. In addition, effects of each drug on respiratory efforts were also evaluated.

Butorphanol showed no analgesic effects against the infrared stimulus. Morphine did show a depressed reaction to the stimulus. Both butorphanol and morphine demonstrated respiratory depressive effects.

One study has been performed using NSAIDS in reptiles. In that study Ball Pythons were pre-treated with meloxicam, 0.3 mg/kg, SC prior to surgical catheterization. Various physiological parameters such as plasma catecholamines, cortisol, blood pressure, heart rate and blood gas values were measured. Per the authors, there was no significant difference between snakes that received meloxicam compared to a saline control. NSAIDS may have a place in treating acute and chronic pain in reptiles, but safe, effective doses need to be established, and caution must be taken regarding renal function and gastrointestinal effects as seen in mammalian patients.

Conclusion

To date there have been no definitive studies in reptiles that demonstrate what would be the best analgesics. Practitioners should use care when selecting analgesics based solely on limited experience in the various species. In my hospital I use buprenorphine, 0.03 mg/kg, IM, q 24h prn.

References

1.  Read MR. JAVMA. 2004;224(4):547.

2.  Greenacre CB, et al. JHMS 2006;16(3)88.

3.  Sladky K. Proc. ARAV. 2007; New Orleans, LA. 51.

4.  Olesen MG. JAVMA. 2008; 233(12)1806.