A 20 years old nulliparous women is an oral contraceptives pills. She is currently diagnosed as having pulmonary tuberculosis which anti-tuberculous drug decreases the effect of OCP.
**Core Concept**
Pulmonary tuberculosis treatment involves the use of multiple anti-tuberculous medications, some of which interact with oral contraceptives (OCPs) by inducing enzymes that metabolize OCP components, thereby decreasing their efficacy.
**Why the Correct Answer is Right**
Rifampicin, a key anti-tuberculous medication, is a potent inducer of the cytochrome P450 enzyme system, specifically CYP3A4. This enzyme system is responsible for metabolizing ethinyl estradiol and other components of OCPs. By inducing CYP3A4, rifampicin accelerates the metabolism of OCPs, leading to decreased plasma concentrations and reduced efficacy. This interaction necessitates the use of alternative or additional contraceptive measures to prevent unintended pregnancy.
**Why Each Wrong Option is Incorrect**
**Option A:** Isoniazid does not significantly induce CYP3A4 and is not known to interact with OCPs in a clinically significant manner.
**Option B:** Pyrazinamide may have some effect on CYP3A4, but it is not as potent an inducer as rifampicin and is not primarily responsible for the interaction with OCPs.
**Option C:** Ethambutol does not have a significant effect on CYP3A4 and is not known to interact with OCPs.
**Option D:** Streptomycin is an aminoglycoside antibiotic that does not interact with OCPs.
**Clinical Pearl / High-Yield Fact**
When managing patients on OCPs who are also receiving anti-tuberculous therapy, consider alternative or additional contraceptive measures, such as progestin-only pills, intrauterine devices (IUDs), or barrier methods, to prevent unintended pregnancy.
**Correct Answer: B. Pyrazinamide may have some effect on CYP3A4, but it is not as potent an inducer as rifampicin and is not primarily responsible for the interaction with OCPs.