Q1. Which antituberculous drug causes optic neuritis? A. Rifampicin B. Isoniazid C. Pyrazinamide D. Ethambutol ANSWER: D — Ethambutol. Why: it causes dose-related optic neuritis affecting acuity and colour discrimination. "E for Eyes." A: orange body fluids and hepatitis. B: peripheral neuropathy. C: hyperuricaemia and hepatitis. LEARNING POINT: each first-line drug has one defining toxicity; know which nerve or organ each targets.

Q2. Why is pyridoxine given alongside isoniazid? A. To improve absorption B. To prevent peripheral neuropathy C. To prevent optic neuritis D. To reduce hepatotoxicity ANSWER: B — to prevent peripheral neuropathy. Why: isoniazid interferes with pyridoxine (vitamin B6) metabolism, and the resulting deficiency causes peripheral neuropathy. Supplementation prevents it. C: that is ethambutol's toxicity, and pyridoxine does not prevent it. LEARNING POINT: routine in malnutrition, pregnancy, alcohol dependence, diabetes, HIV and CKD.

Q3. An asymptomatic 28-year-old has a positive IGRA on pre-employment screening. Chest X-ray is normal. The correct management is: A. Full RIPE therapy for 6 months B. Exclude active disease, then offer preventive therapy C. No action — the test is a false positive D. Repeat the IGRA in one year ANSWER: B. Why: a positive IGRA indicates infection. With no symptoms and a normal film, this is LATENT TB, treated with preventive therapy rather than a full multi-drug regimen. A: over-treatment for latent infection. C: BCG does not cause a false positive IGRA. LEARNING POINT: the test proves infection, not disease.

Q4. A patient with HIV starts antiretrovirals three weeks into TB treatment. Two weeks later fever and lymphadenopathy worsen, but TB cultures show a good response. The most likely explanation is: A. Treatment failure B. MDR-TB C. Immune reconstitution inflammatory syndrome D. Drug-induced fever from rifampicin ANSWER: C — IRIS. Why: as antiretrovirals restore immune function, the recovering immune system reacts vigorously to residual mycobacterial antigen, producing paradoxical worsening despite genuine microbiological improvement. A, B: contradicted by the good culture response. LEARNING POINT: IRIS signals immunity returning. Continue both treatments; do not stop.

Q5. A patient with a three-week cough, night sweats and weight loss has a NEGATIVE sputum smear. The correct next step is: A. Exclude TB and treat as pneumonia B. Send for molecular testing and culture, and treat on clinical suspicion if indicated C. Repeat the smear in three months D. Start RIPE only if a second smear is positive ANSWER: B. Why: smear microscopy has limited sensitivity and requires a high bacillary load, so a negative result cannot exclude TB in a clinically compatible case. Molecular testing gives a rapid answer including rifampicin resistance. A: the dangerous conclusion this question targets. LEARNING POINT: a negative smear never excludes TB.

Q6. A woman on the combined oral contraceptive pill starts TB treatment. The most important counselling point is: A. The pill will work normally B. Rifampicin induces CYP450 and reduces contraceptive efficacy — use an alternative method C. Isoniazid inactivates the pill D. She should stop the pill permanently ANSWER: B — rifampicin is an enzyme INDUCER. Why: it accelerates metabolism of oestrogen and progestogen, so contraceptive efficacy falls and pregnancy can occur. Alternative or additional contraception is needed. C: isoniazid is an enzyme INHIBITOR, not an inducer, and is not the issue here. LEARNING POINT: rifampicin interacts with a long list of drugs — always check what else the patient takes.

Q7. Why is tuberculosis treated with four drugs simultaneously rather than one? A. Four drugs kill faster than one B. To prevent selection of spontaneously resistant mutants C. Because each drug treats a different organ D. To shorten treatment to two weeks ANSWER: B — to prevent resistance. Why: mutations conferring resistance to any single drug arise naturally in a large bacillary population. Monotherapy simply selects for them. Simultaneous resistance to four unrelated drugs is vanishingly rare. A: potency is not the primary reason. D: treatment still takes months. LEARNING POINT: combination therapy denies resistance a foothold — and interrupted treatment reopens that door, which is how MDR-TB arises.