Transient cimetidine resistance.

We report the phenomenon of transient resistance to cimetidine in a 27-year-old healthy, asymptomatic woman who underwent a 5-day gastric intubation study as part of a research protocol. Despite normal blood levels after orally administered cimetidine, this subject had no gastric acid suppression in response to the drug on 2 days of the protocol. On two other occasions, however, she responded appropriately to cimetidine by raising her intragastric pH, reaching peak cimetidine blood levels that were similar to those on the days that she had not responded. The cause for this variable effect of cimetidine on intragastric pH is not known, but might reflect a cholinergic response to stress. Other mechanisms for cimetidine resistance are also discussed.