Which substance is a known inhibitor of CYP3A4?

CYP3A4 is a crucial enzyme in the liver that metabolizes a wide range of medications. When medications or substances inhibit this enzyme, they can lead to increased levels of drugs that are normally metabolized by CYP3A4, which may enhance the effects or increase the likelihood of adverse effects.

The correct answer identifies a substance known to inhibit CYP3A4. This substance interacts with the enzyme, blocking its activity and thereby preventing the normal metabolic breakdown of other drugs. Consequently, this inhibition can result in higher plasma concentrations of those drugs, necessitating careful monitoring and possible dose adjustments.

In contrast, many other substances can either be inducers or have minimal effects on CYP3A4. For instance, St John's Wort and Carbamazepine are generally known as inducers rather than inhibitors of this enzyme, leading to decreased concentrations of co-administered drugs. Amlodipine also does not have significant inhibitory effects on CYP3A4. Understanding these interactions is vital for predicting drug-drug interactions and safely managing patient medication regimens.