Relative bioavailability of oral sustained-release and regular-release oxprenolol tablets at steady-state

The relative bioavailability of a test sustained-release (SR) oxprenolol tablet against an approved regular-release (RR) tablet has been investigated at steady-state. In a randomized two-way crossover study, one tablet of 160mg SR oxprenolol once every 24 h and one tablet of 80 mg RR oxprenolol once every 12 h were given to 12 healthy volunteers for 5 days. Blood samples were collected from each subject just prior to each dose-administration on days 1 through 4, and at scheduled time points on day 5 and analysed for oxprenolol concentration using HPLC. The SR tablet resulted in 42 per cent reduction in mean peak drug levels (p = 0·0341) and a statistically non-significant 14 per cent increase in mean trough levels (p = 0·8357) than the RR tablet. However it required 160 per cent longer time to reach average steady-state concentrations (CSS) on day 5 (1·38h for SR versus 0·53 h for RR; p =0·0205). The mean area under the plasma drug concentration—time curve at steady state (AUC96-120) with the SR tablet was ∼ 18 per cent lower than that observed with the RR tablet, and the degree of fluctuation (DF) was reduced by 30 per cent (2·81 for SR versus 4·11 for RR;p = 0·0069). On average, a single dose of SR tablet and two doses of RR tablets maintained the drug levels above a constant CSS of 204·6 ngml−1 for 7·88 and 7·65 h, respectively (p = 0·3513).