SBA — Single Best Answer · Review
Question 476
Pharmacology → General
Classification
Question
SSBAQuestion Header
A woman taking a combined oral contraceptive starts long-term treatment with a drug that induces hepatic microsomal enzymes. Which combination of drug and pharmacological consequence is most consistent with this interaction?
Question Stem
Select the single best answer.
Options
A
Fluconazole — approximately 40% reduction in contraceptive hormone levels
B
Erythromycin — approximately 40% reduction in contraceptive hormone levels
C
Carbamazepine — approximately 40% reduction in contraceptive hormone levels
D
Cimetidine — approximately 40% reduction in contraceptive hormone levels
E
Ketoconazole — approximately 40% reduction in contraceptive hormone levels
Explanation
Hepatic enzyme induction can lower oral contraceptive hormone levels by approximately 40%. Carbamazepine is an enzyme-inducing antiepileptic drug and is therefore the best answer. Phenytoin and rifampicin are also listed among hepatic enzyme inducers, whereas fluconazole, erythromycin, cimetidine and ketoconazole inhibit hepatic enzyme activity.
Option Validity
A) Fluconazole inhibits rather than induces hepatic enzyme activity.
B) Erythromycin inhibits rather than induces hepatic enzyme activity.
D) Cimetidine inhibits rather than induces hepatic enzyme activity.
E) Ketoconazole inhibits rather than induces hepatic enzyme activity.
Further Reading
Saxena R. Textbook for MRCOG-1. Chapter 12: Pharmacology. Clinical Pharmacy, p.344.