Cimetidine inhibits which liver enzyme, thereby prolonging the effects of other drugs?

Cimetidine is known to inhibit the cytochrome P450 enzyme system, which is a group of enzymes involved in the metabolism of many drugs. Specifically, cimetidine primarily interferes with the CYP1A2 and CYP2C19 enzymes but also has effects on several others in the P450 family. This inhibition can lead to prolonged effects of other drugs that are metabolized by the same pathways, as it decreases the metabolism of these medications, increasing their plasma concentrations and potentially leading to toxicity.

In the context of the choices, the option that refers to the P450 enzyme system is the broadest and correctly encompasses the action of cimetidine in terms of drug interactions. This is important for practitioners to understand, as it highlights the need to monitor patients for potential interactions and side effects when cimetidine is prescribed along with other medications that rely on the P450 pathway for metabolism.

The other enzymes listed, such as CYP3A4, are specific members of the P450 family, and while cimetidine can inhibit CYP3A4, the broader classification as the P450 system provides a more encompassing view of its effects on drug metabolism. Understanding this principle is crucial for safe prescribing practices in the management of patients.