1 The effect of ranitidine 300 mg once daily and cimetidine 800 mg once daily on the disposition of nifedipine was studied in two groups of 12 volunteers. Both investigations were placebo-controlled cross-over studies. 2 The first group received ranitidine, cimetidine or placebo for 5 days with 20 mg nifedipine given on the 5th day. Each period was separated by 1 week. The second group received nifedipine 10 mg three times daily for 5 days together with the H2-receptor antagonist or placebo. 3 Cimetidine produced a significant increase in the AUC of both single and steady state dosing of nifedipine. Peak nifedipine levels were significantly increased only in the chronic dose study compared to placebo. 4 Ranitidine did not produce any significant changes in either study.

There are no pharmacokinetic grounds for adjusting dosages of either ropinirole or L-dopa when given in combination.

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These results therefore indicate that on pharmacokinetic grounds no dose adjustment is necessary for digoxin co-administered with ropinirole.