ethambutol hydrochloride: clinical use

Prescribing considerations

• Use only in an appropriate multidrug regimen; resistant M. tuberculosis strains can emerge readily with monotherapy.
• Assess whether the patient can recognise and report visual changes; consider additional ophthalmological support for children or people unable to self-monitor.
• Ethambutol is preferably avoided in renal impairment because accumulation increases toxicity risk.
• Consider hyperuricaemia or gout and previous serious ethambutol-associated skin reactions.

Contraindications and cautions

• Hypersensitivity to ethambutol or a product excipient.
• Known optic neuritis or poor vision, unless clinical judgement determines treatment is necessary.
• Do not restart after ethambutol-associated Stevens–Johnson syndrome, toxic epidermal necrolysis or DRESS.

Monitoring

• Check renal function before treatment.
• Perform baseline ophthalmic assessment including visual acuity, colour vision, perimetry and ophthalmoscopy; test each eye separately.
• Ensure immediate review of new visual symptoms and discontinue promptly when ethambutol toxicity is suspected.
• Consider plasma concentration monitoring when renal impairment necessitates use.
• Check liver function if hepatitis symptoms or unexplained general illness develop.

Clinical pharmacology

Ethambutol is bacteriostatic and inhibits mycobacterial cell-wall arabinosyltransferases. Food does not significantly affect oral absorption. Most absorbed medicine is eliminated unchanged in urine, making renal function an important determinant of exposure.

Formulation and product differences

• The selected product is a grey, circular, biconvex film-coated tablet supplied in aluminium/PVC blister packs.
• It is essentially sodium-free and should be stored below 25°C.

Tablet

Route: Oral

Strengths: 100 mg, 400 mg