Abstract

Thiafentanil has been in the pharmaceutical development and registration pipeline for use in hoofstock for almost 20 yr. During that time, it has been used by hundreds of veterinarians in zoos and free ranging situations in which useful data and experience has been collected. As it is now fully approved in South Africa and exported to numerous countries from there and nearing a FDA MUMS Index approval here in the US, this may be an appropriate time to give a broad overview of its comparative applications, advantages and disadvantages to the currently available potent opiates etorphine and carfentanil.

Etorphine has been used in wildlife and zoological medicine for over 60 yr. Its advantage is that it has been used in almost every species possible. The knowledge base as to what combinations of alpha-two agonists, butyrophenone, or dissociative with etorphine is effective in what species is vast. Concurrently, we have discovered that with etorphine in many species, we experience prolonged excitement phases during induction, hypertension in many cases, respiratory depression and muscle rigidity. In many species there is more regurgitation with etorphine compared to carfentanil and thiafentanil. Many concurrent uses of the alpha-two’s, azaperone, and the sedatives have been used in an attempt to manage these side effects. Etorphine anesthesia protocols were eventually worked out for most major species, even with its side effects, and became widely used in larger hoof stock and equids.

Carfentanil was first available for use in the early 1980’s. Its first applications were explored in South Africa and later in North America. Its most apparent immediate advantages over etorphine were the low dose volumes possible and slightly shortened induction times in many key species. It still had most of the classical opiate issues such as muscle rigidity, respiratory depression and hypertension that had to be managed. It was rapidly learned that wild members of the Perissodactyla were refractory to its effect or showed more adverse side effects-much to the dismay of the wildlife medicine community.

Thiafentanil oxalate (A3080, Thianil) was first available for field use in the early 1990’s. The first field reports and publications immediately demonstrated the dramatically shortened induction times in most species. Its expanded field use demonstrated improved efficacy in many species and it now is considered the drug of choice for hoofstock such as gemsbok (Oryx gazella), Liechtenstein’s hartebeest (Sigmoceros lichtensteini), impala (Aepyceros melampus), kudu (Tragelaphus strepsiceros), nyala (Tragelaphus angasii), reedbuck (Redunca sp), rhebok (Pelea caoreolus), roan (Hippotragus equinus), sable (Hippotragus niger), waterbuck (Kobus ellipsiprymnus), and klipspringer (Oreotragus oreotragus).¹ Published reports indicate that it is also the opiate of choice for use in giraffe (Giraffa camelopardalis ).² Field work in Thailand also indicate that it is the drug of choice for gaur (Bos gaurus ) and banteng (Bos javanicus) (M. Bush, pers. comm., 2012). With all this success in these species, the Perissodactyla remain refractory to thiafentanil, and etorphine remains the drug of choice for these species as well as the rhino and elephant, although field use of thiafentanil in elephant and rhino is becoming more common in Africa (J. Raath, pers. comm., 2012). The rapid metabolism of thiafentanil may be a drawback in some situations as supplementation may be necessary before all procedures are completed in contrast to the longer metabolic half-life of etorphine and carfentanil.

In North America due to the improved shortened induction period of thiafentanil in species such as elk, it has become the drug of choice for aerial capture for this species.³ The reduced induction time enables immobilization of more animals with less helicopter time. Its efficacy in pronghorn makes it the only drug that will reliably immobilize this species.⁴

Based on the published literature and the field reports available today, it is most probable that thiafentanil will replace both carfentanil and etorphine in most free ranging hoof stock, other than the Perrisodactylids, due to its shortened induction time, low dose volume, and fewer side effects in some species. Etorphine will remain in use as the drug of choice in the Perrisodactylids for the foreseeable future.

Literature Cited

1.  Kock, M. D., D. Meltzer and R. Burroughs. 2006. Chemical and Physical Restraint of Wild Animals. IWVS PO Box 106, Greyton South Africa. 292.

2.  Citino, SB, M Bush, W Lance, M Hofmeyr, and D Grobler. 2006. Use of thiafentanil (A3080), medetomidine and ketamine for anesthesia of captive and free-ranging giraffe (Giraffa camelopardalis). Proc. Conf. Amer. Assoc. Zoo Vet. Tampa, Florida. 211–212.

3.  Hunter, D. L, K Hamlin, and M Ross. 2005. Helicopter immobilization of free ranging elk (Cervus elaphus) with A3080. Proceedings Wildl Dis Assoc Ann Mtn..

4.  Kreeger, TJ, WE Cook, CA Piche, and T Smith. 2001. Anesthesia of pronghorns using thiafentanil or thiafentanil plus xylazine. J Wildl. Mgmt. 65(1): 25–28.