Ethambutol

How it works

It inhibits arabinosyl transferases involved in mycobacterial cell-wall arabinogalactan synthesis, producing a bacteriostatic effect against Mycobacterium tuberculosis.

Prescribing in practice

• Dose-related optic neuritis causing reduced visual acuity and red-green colour blindness is the key toxicity, so baseline visual assessment is required and the drug must be stopped if visual changes occur.
• It is renally cleared and the dose must be reduced and monitored in renal impairment to avoid accumulation and ocular toxicity.
• It must always be used within a multidrug regimen to prevent emergence of resistance, never as monotherapy.

Monitoring

Assess visual acuity and colour vision at baseline and review eyesight at each visit, with renal function monitoring particularly where impairment is present.

Counselling the patient

• Report any blurring, change in colour vision or reduced sight immediately and stop the tablets.
• Take all anti-tuberculosis medicines exactly as directed for the full course.
• Children unable to report visual symptoms reliably need careful clinical consideration.

Evidence & guidelines

A standard component of WHO and NICE-endorsed first-line quadruple therapy for drug-sensitive tuberculosis.