A 40-year-old woman on RHZE for TB develops progressive painless blurring of vision and impaired red-green colour discrimination. Fundoscopy is normal. Which drug should be discontinued?
- A Rifampicin
- B Ethambutol ✓
- C Pyrazinamide
- D Isoniazid
Correct answer: B. Ethambutol
Explanation
Ethambutol causes dose-related optic neuropathy affecting the central fibres of the optic nerve, presenting with retrobulbar neuritis, impaired visual acuity, and red-green colour blindness. Fundoscopy may be normal early (retrobulbar). The drug chelates copper and zinc, causing mitochondrial dysfunction in optic nerve axons. Peripheral neuropathy is seen with isoniazid.
Reference: Katzung Basic and Clinical Pharmacology, 15th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.