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 160 mg 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 (1.38 h 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 approximately 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 ng ml-1 for 7.88 and 7.65 h, respectively (p = 0.3513).