A woman taking oestradiol is to have an extraction. All of the following are accurate statements about prescribing an antibiotic EXCEPT one. Which is the EXCEPTION?

Correct answer: A. Antibiotics reliably reduce the effectiveness of hormonal contraception

• A. CORRECT — this is the EXCEPTION, because the statement is not accurate as an absolute. The long-taught claim that antibiotics generally impair hormonal contraception is NOT supported by current evidence. The only antibiotics with a proven interaction are the RIFAMYCINS (rifampin, rifabutin), which are potent CYP450 inducers, and possibly griseofulvin. For amoxicillin, clindamycin, metronidazole, doxycycline and the rest, no reliable reduction in contraceptive efficacy has been demonstrated.
• B. This IS accurate. Metronidazole potentiates warfarin and reacts with alcohol; macrolides inhibit CYP3A4; tetracyclines chelate with calcium and iron.
• C. This IS accurate. Nausea, diarrhoea and antibiotic-associated colitis are common, and clindamycin in particular carries a Clostridioides difficile risk.
• D. This IS accurate. Hypersensitivity reactions and antimicrobial resistance are the standard risks of any antibiotic prescription.

Note: ⚑ Worth discussing in the group, since older board material and some patient information leaflets still state the interaction as fact. Many clinicians still advise additional contraceptive precautions as a precaution, and doing so is defensible — but the EVIDENCE supports it only for the rifamycins. Note separately that a general anesthetic or severe vomiting and diarrhoea from an antibiotic CAN reduce absorption of an oral contraceptive.