Butorphanol and Butorphanol/Diazepam Administration for Analgesia and Sedation of Harbor Seals (Phoca vitulina)
Butorphanol tartrate is a synthetic opioid agonist/antagonist which has recently become a popular choice for preanesthesia and pain relief in small and large domestic animal medicine.1-4,6 The dosage recommendation for dogs is 0.2–0.4 mg/kg body weight IM or SC, producing safe and effective analgesia with the added benefit of mild sedation. Butorphanol provides analgesia 4–7 times more potent than morphine occurring within 30 min and lasting 2–3 h with minimal cardiovascular or respiratory side effects.5 Drug effects can be rapidly reversed with naloxone. The use of butorphanol in wildlife has not been widely reported but deserves further attention.
Current nutritional research on harbor seals at the Alaska SeaLife Center requires multiple samples of blood, blubber, and deep muscle biopsy specimens over each 4-month trial. Due to the risk of complications sometimes encountered with standard general anesthesia protocols, we have been using the analgesic and mild sedating effects of butorphanol both alone and in combination with reduced doses of diazepam for these minimally invasive procedures.
Butorphanol is administered at 0.4 mg/kg body weight by deep intramuscular injection in the gluteal region 5–20 min prior to procedures. Where possible, this dose is administered under voluntary behavioral control and the seal is allowed to rest undisturbed for several minutes prior to further handling. Animals typically show decreased anxiety and are sufficiently relaxed within 10 min for procedures such as radiographic positioning or skin scrapings. For blubber biopsies, a simple seat belt and stretcher system is used to prevent the animal from moving away during sampling and 1–2% lidocaine is injected for local anesthesia at the biopsy sites. Additional relaxation has been induced by intravenous injection of a low doses of diazepam (0.2 mg/kg body weight) to facilitate procedures such as deep muscle biopsy, endoscopic examinations, and procedures involving the eyes and head. Respiratory depression has not been observed with butorphanol alone but did occur transiently in one obese seal given 0.28 mg/kg diazepam IV 90 min after a standard butorphanol dose. The harbor seals show some degree of lethargy for 1–4 h after intramuscular injection with butorphanol but remain responsive to commands and will eat and swim normally within 1 h.
The use of butorphanol as a single agent appears safe and effective for minor procedures. Premedication with butorphanol allows effective sedation and relaxation with lower doses of diazepam, reducing the risk of respiratory depression. Residual analgesia is a benefit in minor surgical procedures in reducing postoperative discomfort.
1. Dyson, D.H. and M. Atiloal. 1992. A clinical comparison of oxymorphone-acepromazine and butorphanol-acepromazine sedation in dogs. Vet Surg. 21(5):418–421.
2. Houghton, K.J., R.H. Rech, D.C. Sawyer, R.A. Durham, T. Adams, M.A. Langham, and E.L. Striler. 1991. Dose response of intravenous butorphanol to increase visceral nociceptive threshold in dogs. In: Proc Soc Exp Biol Med. 197(3):290–296.
3. Lin, H.C., G.J. Benson, J.C. Thurmon, W.J. Tranquilli, W.A. Olson, and R.F. Bevill. 1993. Influence of anesthetic regimens on the perioperative catecholamine response associated with onychectomy in cats. Am J Vet Res. 54(10):1721–1724.
4. Orsini, J.A. 1988. Butorphanol tartrate: pharmacology and clinical indications. Comp Eq. 10(7):849–854.
5. Plumb, D.C. 1999. Butorphanol tartrate. In: Veterinary Drug Handbook, Pharmavet, White Bear Lake, MN, 99–100.
6. Short, C.E. 1997. Pain management of the injured patient during diagnostic and treatment procedures. In: Pain in Animals, W Vet Conf. Las Vegas, NV, 70–77.