Which adverse effect is likely caused by cimetidine’s interaction with phenytoin in a patient experiencing neurological symptoms?

Cimetidine is known to interfere with the metabolism of various drugs, including phenytoin, which is an antiepileptic medication. The adverse effect resulting from this interaction is primarily due to cimetidine's ability to inhibit cytochrome P450 enzymes in the liver that are responsible for the metabolism of many drugs.

Phenytoin is metabolized through these cytochrome P450 enzymes (primarily CYP2C9 and CYP2C19), and when cimetidine is administered concurrently, it can decrease the metabolic clearance of phenytoin. This results in increased levels of phenytoin in the bloodstream, which can lead to toxicity and neurological symptoms such as dizziness, ataxia, or even convulsions.

Therefore, the inhibition of metabolism caused by cimetidine results in elevated concentrations of phenytoin, which explains the adverse neurological symptoms observed in the patient. Understanding this interaction is crucial for managing patients on both medications effectively.