Cimetidine-Associated Mental Confusion

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Abstract
Cases (15) of cimetidine[a drug used in the treatment of peptic ulcer]-associated mental confusion have recently appeared. Cimetidine serum concentrations in 36 patients was monitored and correlated with changes in mental status. Patients [30] did not change on cimetidine and 6 experienced moderate to severe mental status changes. These 6 patients had both renal and liver dysfunction (P < 0.05), as well as cimetidine trough concentrations above 1.25 .mu.g/ml (P < 0.05), in close association with mental status changes. The changes in mental status became progressively more severe as trough concentrations rose. Five patients underwent lumbar punctures. The CSF to serum ratio of 0.24:1 indicates that cimetidine passes the blood-brain barrier, and this raises the possibility that mental status changes are due to blockade of CNS histamine H2 receptors. A subgroup at high risk for both elevated troughs and mental confusion was identified. These patients with severe compromise of both renal and hepatic excretory systems must be closely observed and given reduced cimetidine doses if side effects are to be avoided.