Biopharmaceutical evaluation of transnasal, sublingual, and buccal disk dosage forms of butorphanol

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Abstract
A series of three-way crossover randomized studies were conducted to evaluate the absolute bioavailability of butorphanol, a potent agonist-antagonist analgesic, from transnasal, sublingual, and buccal disk formulations in order to identify a practical alternative to oral administration. In each study, healthy male volunteers received 2 mg doses of butorphanol tartrate intravenously and either transnasally, sublingually or buccally. Serial blood samples were collected over 12 h and butorphanol plasma concentrations were determined by radioimmunoassay. The plasma concentration data were subjected to non-compartmental pharmacokinetic analysis. The elimination half-life of butorphanol was about 3–5 h and was independent of the route of administration. Absorption of butorphanol following transnasal administration was faster than that observed following sublingual or buccal administration. Mean absolute bioavailabilities of sublingual tablet and buccal disk formulation were only 19 per cent and 29 per cent, respectively, but for transnasal administration the value rose significantly, to 70 per cent. Based on the results of these studies, transnasal dosage form of butorphanol was selected for further clinical trials of treatment of moderate to severe pain.