<prompt> A 30-year-old mother of 2 children weighing 60 kg was taking combined oral contraceptivepill containing levonorgestrel 0.15 mg ethinylestradiol 30 μg per day cyclically 3 weeks treatment1 week gap. She developed fever with cough and was diagnosed as a case of pulmonary tuberculosisafter sputum smear examination. She was put on isoniazid 300 mg rifampin 600 mg pyrazinamide 1.5 g ethambutol 1.0 g daily for 2 months, followed by isoniazid 600 mg rifampin 600 mg thrice weekly. In the 3rd month, she failed to have the usual withdrawalbleeding during the gap period of contraceptive cycle. After 10 days, her urinary pregnancy testwas found to be positive.What could be the reason for failure of the oral contraceptive?Rifampicin is enzyme inducer and induced metabolism of contraceptivesEthambutol is enzyme inducer and induce metabolism of contraceptivesBothNone  <response>: Rifampin is known to induce the metabolism of contraceptive steroids. Thus, after regular intake of rifampin for more than 2 weeks needed for enzyme induction the steady-state blood level of levonorgestrel and ethinylestradiol could have fallen below the threshold for inhibition of ovulationcontraception. As such, fertility was restored and the woman conceived. 