Beclomethasone dipropionate: absolute bioavailability, pharmacokinetics and metabolism following intravenous, oral, intranasal and inhaled administration in man

Aims To assess the absolute bioavailability, pharmacokinetics and metabolism of beclomethasone dipropionate (BDP) in man following intravenous, oral, intranasal and inhaled administration. Methods Twelve healthy subjects participated in this seven-way cross-over study where BDP was administered via the following routes. intravenous infusion (1000 mug), oral (4000 mug, aqueous suspension), intranasal (1344 mug, aqueous nasal spray) and inhaled (1000 mug ex-valve, metered dose inhaler). The contribution of the lung, nose and gut to the systemic exposure was assessed by repeating the inhaled, intranasal and oral dosing arms together with activated charcoal, to block oral absorption. Blood samples were collected for 24 h postdose for the measurement of BDP, beclomethasone-17-monopropionate (B-17-MP) and beclomethasone (BOH) in plasma by liquid chrornatography tandem mass spectrometry. Results Intravenous administration of BDP (mean CL 150 1 h(-1), V-ss 20 l, t(1/2) 0.5 h) was associated with rapid conversion to B-17-MP which was eliminated more slowly (t(1/2) 2.7 h). In estimating the parameters for B-17-MP (mean CL 120 1 h(-1), V-ss 424 1) complete conversion of BDP to B-17-MP was assumed. The resultant plasma concentrations of BOH were low and transient. BDP was not detected in plasma following oral or intranasal dosing. The mean absolute bioavailability (%F, 90% CI; nominal doses) of inhaled BDP was 2% (1-4%) and not reduced by coadministration of charcoal. The mean percentage F of the active metabolite B-17-MP was 41% (31-54%), 44% (34-58%) and 62% (47-82%) for oral, intranasal and inhaled dosing without charcoal, respectively. The corresponding estimates of nasal and lung absorption, based on the coadministration of charcoal, were < 1% and 36% (27-47%), respectively. Conclusions Unchanged BDP has negligible oral and intranasal bioavailability with limited absorption following inhaled dosing due to extensive (95%) presystemic conversion of BDP to B-17-MP in the lung. The oral and intranasal bioavailabilities of the active metabolite B-17-MP were high and similar, but direct absorption in the nose was insignificant. The total inhaled bioavailability of B-17-MP (lung + oral) was also high (62%) and approximately 36% of this nas due to pulmonary absorption. Estimates of oral bioavailability and pulmonary deposition based on total BOH were approximately half those found for B-17-MP.