Paper II
2015 September (Supplementary) (2010 Scheme) · 40 marks · 120 min

Question

Read the clinical problem and answer the following questions: A 28 years old woman having two children wanted to follow a contraceptive method. Patient was advised to take oral contraceptive pills. She is a known case of pulmonary tuberculosis for which she is on Rifampicin 450mg. INH300mg and ethambutol 300mg per day.

  • (a) What are the expected complications. 2 mark(s)
  • (b) Why. 2 mark(s)
  • (c) What will you suggest 2 mark(s)
Q26 marksEssays

Answer

(a) Expected complications

  • Contraceptive failure (unwanted/breakthrough pregnancy) with the oral contraceptive pill
  • Breakthrough bleeding/menstrual irregularities

(b) Why

  • Rifampicin is a potent inducer of hepatic microsomal (CYP450) enzymes
  • It significantly increases the metabolism of the oestrogen and progestin components of the oral contraceptive pill, lowering their plasma levels below the threshold needed for reliable contraceptive efficacy — leading to breakthrough bleeding and risk of contraceptive failure

(c) Suggestion

  • Advise the patient to use a non-hormonal/barrier method of contraception (e.g., condoms) or an intrauterine device (IUD) during rifampicin therapy and for some weeks after stopping it, since OCPs cannot be relied upon while on an enzyme-inducing drug like rifampicin
  • Counsel her about this drug interaction explicitly, as this is a well-recognized cause of oral contraceptive failure

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