Abstract

A 16-year-old male Amur tiger was immobilized to attempt alleviation of chronic pain from severe right elbow osteoarthritis by intrathecal injection of resiniferatoxin (RTX). Resiniferatoxin is a naturally occurring compound similar to capsaicin, the active ingredient in hot pepper.^3,5 It is being investigated for the treatment of certain types of chronic pain in humans and dogs.^1,3,4 The tiger’s treatments over the past four years had included several oral, subcutaneous, intramuscular, and intraarticular medications but, despite these treatments, the tiger’s lameness had progressed. The RTX injection was felt to be a last-resort treatment, with the other option considered being euthanasia.

The tiger was immobilized, the dorsal cervical area was surgically prepped, cerebrospinal fluid was collected from the cisterna magna, and then RTX was slowly injected over a period of 15 minutes, followed by a flush of sterile saline. Initial physiologic responses were an increase in heart rate, no change in blood pressure, and a short period of tachypnea followed by apnea. Anesthesia was discontinued and doxapram (Dopram-V, Wyeth-Ayerst Canada Inc., Montreal, Quebec, Canada) was administered to stimulate respiration. Peripheral reflexes slowly returned, but spontaneous respiration never resumed, and the tiger suffered fatal cardiac arrest 3.5 hours after completion of the RTX injection. Necropsy results revealed severe cardiac and vascular amyloidosis, and severe chronic osteoarthritis of the right elbow but no CNS changes attributable to the RTX injection. The respiratory arrest experienced by this tiger suggests either a species-specific reaction to RTX, or an idiosyncratic reaction of this particular individual.

Acknowledgments

The authors would like to thank Rock Boily, Alex Chandonnet, Dr. Mylène-Kim Leclerc, Dr. Marilyn Dunn, and Christopher Scala for their assistance during the tiger procedure; Dr. André Dallaire for the histopathologic interpretation; and the tiger keepers at the Granby Zoo for the biomedical training and unwavering care of the tiger in this report.

Literature Cited

1.  Brown DC, Iadarola MJ, Perkowski SZ, Erin H, Shofer F, Laszlo KJ, et al. Physiologic and antinociceptive effects of intrathecal resiniferatoxin in a canine bone cancer model. Anesth. 2005;103:1052–1059.

2.  Karai L, Brown DC, Mannes AJ, Connelly ST, Brown J, Gandal M, et al. Deletion of vanilloid receptor 1-expressing primary afferent neurons for pain control. J Clin Invest. 2004;113:1344–1352.

3.  Long AC, Medeiros DM. Evaluation of capsaicins use in analgesic medicine. J Nutraceut Funct Med Foods. 2001;3:39–46.

4.  Messeguer A, Planells-Cases R, Ferrer-Montiel A. Physiology and pharmacology of the vanilloid receptor. Curr Neuropharm. 2006;4:1–15.

5.  Szallasi A, Blumberg PM. Vanilloid (capsaicin) receptors and mechanisms. Pharm Rev. 1999;51:159–211.