Pharmacokinetics of a single dose of phenylpropanolamine following oral administration at two different times of the day

Pharmacokinetics of a single oral dose of phenylpropanolamine (CAS 154-41-6 ) was investigated by administering 50 mg of the drug at 10.00 and 22.00 h to 8 healthy male volunteers in a crossover design with a wash-out period o f 10 days. Serum samples were analysed for phenylpropanolamine using high p erformance liquid chromatography. Pharmacokinetic parameters were calculate d using model independent method. A significant (p < 0.05) elevation in C-m ax (227.45 versus 181.98 mu g/l) was observed following the drug administra tion at 22.00 h as compared to 10.00 h. These variations may be due to circ adian changes in gastric pH contributing to the time dependent changes in t he absorption of the drug.