Drug reference

Ethambutol

First-line antitubercular agent · Anti-tuberculosis drug

Also known as Ethambutol HCl

START

Baseline visual acuity, color vision (Ishihara plates), fundoscopy. Baseline LFTs and uric acid. Ensure combination therapy (never monotherapy for TB).

TYPICAL MAX

2.5g/dose. Use 15mg/kg for elderly and renal impairment to reduce optic neuropathy risk. Doses >20mg/kg increase optic neuritis risk.

STOP IF

Any visual changes (decreased acuity, color vision loss, visual field defects), severe rash, severe hyperuricemia with gout symptoms.

WATCH

Monthly eye exams (visual acuity, color vision, visual fields) during therapy. Optic neuritis is typically bilateral and reversible if drug stopped promptly. Hyperuricemia is common but usually asymptomatic. Renal function affects clearance—adjust dose if CrCl <30.

CDSCO approvedSchedule HJan AushadhiATC J04AK02

Dose laddermg/d

Renal dose adjustmenteGFR mL/min/1.73m²

KDIGO 2024 + manufacturer label

Pharmacokineticsplasma · t hours

ONSET: 30min · Onset ~30 min
PEAK: 3h · Tmax 2-4 hours
t½: 3.5h · t½ ~3-4 hours
DURATION: 1d · 24 hours (QD)

EXCRETION

Renal unchanged (~50%)

route + CYP

INTERACTIONS

6 major

SEVERE in our sources

PREGNANCY

Safe in pregnancy—no teratogenic effects documented. Essential component of standard TB regimens in pregnancy.

FDA category + note

Top interactionssee all 12 →

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Available in India

101 branded formulations. Look up specific brands in the Drugs workspace.

Jan Aushadhi — generic available at GoI pharmacies

Mechanism

Inhibits arabinosyl transferase enzymes involved in the polymerization of arabinogalactan, an essential component of the mycobacterial cell wall. Specifically inhibits synthesis of arabinogalactan and lipoarabinomannan. Bacteriostatic against Mycobacterium tuberculosis.

Indications

Tuberculosis (active disease—first-line, in combination)Atypical mycobacterial infections (M. avium complex, M. kansasii—in combination)Mycobacterium marinum infections

Dosing

Adult: Active TB: 15-25mg/kg PO daily (max 2.5g) or 50mg/kg 2-3x/week (DOT, max 2.5g). Usually 15-20mg/kg daily in standard 4-drug regimen. MAC: 15mg/kg daily with clarithromycin + rifabutin.
Pediatric: 15-25mg/kg/day PO (max 2.5g). Use with caution in children unable to report visual changes.
Renal adjustment: CrCl <30: 15-25mg/kg 3x/week (avoid daily dosing); or reduce dose 50%.
Hepatic adjustment: No adjustment needed (minimal hepatic metabolism).
Geriatric: Use 15mg/kg (lower end); increased optic neuropathy risk with age; monthly eye exams essential.
Max dose: 2.5g/dose

Pharmacokinetics

Onset

Bacteriostatic effect; clinical improvement 2-4 weeks

Peak effect

Tmax 2-4 hours; CSF penetration: 10-50% of serum (inflamed meninges)

Duration

24 hours (QD dosing)

Half-life

~3-4 hours; prolonged to ~8 hours in renal impairment

Bioavailability

~80%

Protein binding

~20-30%

Metabolism

Minimal hepatic metabolism; ~50% converted to inactive aldehyde and dicarboxylic acid metabolites

Excretion

~50% unchanged in urine; ~15% fecal; ~8% as inactive metabolites

Contraindications

Optic neuritis (pre-existing)
Severe visual impairment
Hypersensitivity to ethambutol
Inability to report visual symptoms (young children—relative contraindication)

Side effects

Common

Optic neuritis (dose-dependent; reversible if detected early)Color vision disturbance (red-green discrimination loss)NauseaAnorexiaAbdominal painHyperuricemia (asymptomatic)

Serious

Retrobulbar optic neuritis (reversible with early discontinuation; may be permanent with continued use)
Peripheral neuropathy
Thrombocytopenia
Severe cutaneous reactions
Hepatotoxicity (rare)

Pregnancy & lactation

Pregnancy

Safe in pregnancy—no teratogenic effects documented. Essential component of standard TB regimens in pregnancy.

Lactation

Compatible with breastfeeding; excreted in milk in small amounts. Continue breastfeeding.