Nifedipine serum concentration; effects upon blood pressure and heart rate in normotensive volunteers. 
Nifedipine (10 mg) was administered orally to 8 normotensive volunteers.  Various measurements such as concentration in serum, blood pressure, and heart rate, were made at 0, 20', 40', 1, 2, 3, 4, 6, 8 and 24 h after administration.  The sample serum, internal standard (diethyl 2,6-dimethyl-4-(2-nitrophenyl)-3,5-pyridinedicarboxylate), HCl and NaNO2 were allowed to react and GLC-ECD was carried out after extration with organic solvent.  The retention time was 3 min for nifedipine and 4 min for internal standard.  Absorption curves were classified into 3 types: a rapid absorption rate (2 subjects) in which the maximum measured nifedipine concentration (70-80 ng/ml) was obtained, within 20-40 min after administration, a slower absorption rate (3 subjects) and an intermediate absorption rate (3 subjects) and an intermediate absorption rate (3 subjects).  A decrease in systolic blood pressure was observed, but no significant difference in diastolic blood pressure and heart rate could be noted among the volunteers.