Reduced steady-state plasma concentrations of chlorpromazine and indomethacin in patients receiving cimetidine

Chronic administration of cimetidine was found to produce a fall in steady-state plasma concentrations of chlorpromazine and of indomethacin in patients. In each case there was some evidence of inhibition of metabolism, suggesting that the mechanism must therefore be decreased absorption sufficient to over-ride the metabolic change. This was confirmed by measurement of excretion of metabolites in the indomethacin study. The fall in indomethacin plasma concentrations was not associated with a change in the clinical effectiveness of the anti-inflammatory therapy.