Professional and Linguistic Assessments Board (PLAB) Practice Exam

Which condition is NOT a common P450 inducer?

1. Rifampin

2. St. John's Wort

3. Griseofulvin

4. Hydrochlorothiazide

The correct answer is: Hydrochlorothiazide

Hydrochlorothiazide is indeed not a common inducer of cytochrome P450 enzymes. This drug primarily functions as a thiazide diuretic and is primarily used to treat hypertension and edema. Its mechanism of action involves the inhibition of sodium reabsorption in the distal convoluted tubules of the kidneys rather than any significant impact on liver enzyme activity. In contrast, Rifampin, St. John's Wort, and Griseofulvin are all known P450 inducers. Rifampin is an antibiotic that is highly effective in treating tuberculosis and is well-documented for its ability to induce various P450 isoenzymes, leading to increased metabolism of other drugs. St. John's Wort is a herbal treatment often used for depression, and it is known to induce several P450 enzymes, reducing the efficacy of various medications. Griseofulvin, an antifungal medication, also exhibits P450 induction properties. Therefore, identifying hydrochlorothiazide as the condition not commonly associated with P450 induction highlights its unique classification as a diuretic rather than a drug that modifies cytochrome P450 activity in the liver.