The absolute bioavailability of transnasal butorphanol in patients experiencing rhinitis

The absolute bioavailability (f) and pharmacokinetics of transnasal butorphanol were evaluated in patients experiencing rhinitis. In an open three-way crossover study, a single 2-mg dose of butorphanol tartrate was administered by intravenous bolus injection (Treatment A), by the transnasal route (Treatment B), or by the transnasal route with pretreatment of the vasoconstrictor, oxymetazoline (Treatment C). Plasma concentrations of butorphanol were determined using a drug specific radioimmunoassay. The pharmacokinetic parameters were derived using the noncompartmental methods. Butorphanol was rapidly absorbed after transnasal administration. The mean maximum concentrations (Cmax) for the transnasal treatment with and without pretreatment of oxymetazoline were 1.61 and 3.01 ng.ml-1, respectively. The corresponding mean absorption times (MAT) were 1.34 and 0.23 h. The mean half-life values were 5.95, 6.28, and 5.77 h, for treatments A, B, and C, respectively. The resulting mean area under the plasma concentration curve (AUC) values were 11.9, 8.6, and 8.07 ng.h.ml-1 for treatments A, B, and C, respectively. The estimates for absolute bioavailability (f) of transnasal butorphanol were 69% and 72% when administered with and without oxymetazoline, respectively. The mean CLT and Vss were 121 l.h-1 and 791 l, respectively, for the intravenous treatment. The pretreatment of oxymetazoline significantly lowered the Cmax and prolonged the absorption time of butorphanol. Although the rate of absorption of transnasal butorphanol was affected by oxymetazoline, the absolute bioavailability in rhinitis patients (72%) was similar to that found with the pretreatment of oxymetazoline (69%) and those reported in healthy volunteers.(ABSTRACT TRUNCATED AT 250 WORDS)