Time dependent pharmacokinetic interaction between phenylpropanolamine and chlorpheniramine maleate in human subjects.

The influence of time of administration on the serum levels of phenylpropanolamine when administered alone and in combination with chlorpheniramine maleate at two different times of a day was studied in healthy human volunteers in a randomized 4 x 4 Latin square crossover design with a washout period of ten days. Blood samples were collected at predetermined time intervals and serum samples were analysed for unchanged phenylpropanolamine using high performance liquid chromatography. The various pharmacokinetic parameters of phenylpropanolamine were calculated using model independent methods. There was a significant (P < 0.05) decrease in the rate of absorption of phenylpropanolamine following its administration in combination with chlorpheniramine maleate at 2200 hours. However, such a change was not observed for treatment at 1000 hours. The observed change may be due to the time dependent gastrointestinal effect of these drugs.