Effect of cimetidine or ranitidine administration on nifedipine pharmacokinetics and pharmacodynamics.

The effect of cimetidine or ranitidine administration on responses to single and multiple doses of nifedipine were studied in 11 subjects who received cimetidine (300 mg q.i.d.) and 12 who received ranitidine (150 mg b.i.d.) in combination with nifedipine. After single doses of nifedipine, cimetidine decreased apparent oral clearance (dose/AUC) from 66 +/- 32 L/hr to 33 +/- 14 L/hr (p less than 0.01); elimination half-life increased from 4.0 +/- 2.2 to 4.9 +/- 2.9 hours (p less than 0.07). Increases in heart rate were greater (26 +/- 13 vs 13 +/- 11 beats/min standing; 19 +/- 11 vs 9 +/- 9 beats/min supine) and lasted longer than after nifedipine alone. Hypotensive effects were similar (10 +/- 7 mm Hg decrease vs 9 +/- 9 mm Hg). During nifedipine multiple-dose administration, cimetidine decreased the apparent oral clearance from 76 +/- 39 to 43 +/- 20 L/hr (p less than 0.01). Blood pressure responses were not altered by cimetidine but heart rate increased more (18 +/- 9 vs 9 +/- 9 beats/min supine; 18 +/- 13 vs 13 +/- 14 beats/min standing). Ranitidine coadministration did not alter nifedipine elimination or dynamic responses. During administration of nifedipine alone, the ratio of oral clearances (multiple to single doses) was 1.1 +/- 0.5. Thus (1) cimetidine but not ranitidine alters responses to nifedipine and (2) nifedipine kinetics do not differ between single- vs multiple-dose conditions.