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
(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
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