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Abstract

Pharmacokinetics of Butorphanol Administered by Four Routes in Cats — A Pilot Study

Angela C. Spann, Gwendolyn L. Carroll, MS, DVM, DACVA

Objective- To evaluate a pilot protocol to determine the optimum sampling time for butorphanol given intravenously (IV, 0.4 mg/kg), orally (PO, 1.0 mg/kg), transdermally (TD, 2.0 mg/kg) and transmucosally (TM, 0.8 mg/kg), using therapeutic target plasma concentrations between 10 and 30 ng mL-1.

Design- Randomized crossover design; each cat received each treatment.

Animals- Two healthy eight month-old purpose-bred male neutered cats.

Procedure- Butorphanol was administered at each dose to each cat with a two week wash-out period between treatments.  Blood samples were collected at 0, 2, 5, 10, 15, 30, and 60 minutes and 2, 3, 4, 6, 8, and 12 hours for the IV trial, and at 0, 5, 10, 20, 30, 45, and 60 minutes and 2, 3, 4, 6, 8, and 12 hours for the PO, TD, and TM trials.  Plasma butorphanol versus time curves were subjected to pharmacokinetic analysis.

Results- Preliminary data from the IV trial from one cat indicates that apparent volume of distribution at steady state after administration of butorphanol was 25.8 L kg-1 and total body clearance was 0.073 L kg-1 minute-1. Extrapolated peak plasma concentration was 169.6 ng mL-1 and elimination half-life was 4.37 hours.

Clinical Significance- Injectable butorphanol is an approved analgesic in cats in the US.  Although often used intravenously, alternative routes of administration (e.g., PO, TM, TD) are appealing because of their convenience and safety, particularly when used at home.  However, use of alternative routes should be based on scientific data that describe butorphanol's availability, distribution, and duration of action.