The effect of cimetidine on the pharmacodynamics of theophylline-induced seizures and ethanol hypnotic activity

Due to its availability as an over-the-counter drug, the use of cimetidine is increasing, thus adverse interactions with other commonly used agents ma y also increase. The aim of this study was to investigate whether acute adm inistration of cimetidine could alter the pharmacodynamics of theophylline neurotoxicity and the hypnotic action of ethanol. To examine these question s, rats received a dose of 77 mg/kg cimetidine followed by a constant infus ion of either theophylline (1.2 mg/min.) or ethanol (16.3 mg/min.) until th e onset of the pharmacological end point, maximal seizure or loss of righti ng reflex, where samples of blood and brain were obtained and assayed for e ither theophylline or ethanol. We report that cimetidine in doses that may cause pharmacokinetic interactions did not affect the concentration-effect relationship of either the stimulating action of theophylline or the depres sant activity of ethanol. These outcomes emphasize the relative safety whic h patients using cimetidine in self-medication rely on.