Cimetidine-theophylline complex formation

Cimetidine forms a complex with theophylline in vitro in both pH 7.4 buffer and human plasma. The increase in the amount of theophylline in solution is about 20% in the buffer system and about 36% in plasma. It is hypothesized that this complex formation may contribute to and be part of the mechanism of the clinically observed decreased theophylline clearance in man in presence of cimetidine.