Group: antimycobacterial agent
Tablet 100-400 mg (hydrochloride)
A synthetic congener of 1,2-ethanediamine that is bactericidal against some nonspecific mycobacteria.
It is readily absorbed from the gastrointestinal tract. Plasma concentrations peak in 2-4 hours and decay with a half-life of 3-4 hours. Ethambutol is excreted in the urine both unchanged and as inactive hepatic metabolites. About 20% is excreted in the faeces as unchanged drug.
In combination with rifampicin and isoniazid in the treatment of infections due to M. kansasii, M. malmoense, M. xenopi and, in immunocompetent hosts, the M. avium-intracellulare complex.
Dosage and administration
Adults: 25 mg/kg daily for no more than 2 months followed by 15 mg/kg daily; or 40 mg/kg three times weekly for 2 years.
Children: 15 mg/kg daily for 2 years.
There is some evidence to suggest that M. kansasii infections require treatment for only 1 year.
Dosage must always be carefully calculated on a weight basis to avoid toxicity, and should be reduced in patients with impaired renal function.
• Known hypersensitivity.
• Pre-existing optic neuritis from any cause.
• Inability (for example due to young age) to report symptomatic visual disturbances.
• Creatinine clearance of less than 50 ml/ minute.
Patients should be advised to discontinue treatment immediately and to report to a doctor should their sight or perception of colour deteriorate. Patients who are too young or who are otherwise unable to comprehend this warning should not receive ethambutol.
Whenever possible, renal function should be assessed before treatment.
Use in pregnancy
Treatment should not be interrupted or postponed during pregnancy.
Dose-dependent optic neuritis can readily result in impairment of visual acuity and colour vision. Early changes are usually reversible, but blindness can occur if treatment is not discontinued promptly.
Signs of peripheral neuritis occasionally develop in the legs.
Emesis and gastric lavage may be of value if undertaken within a few hours of ingestion. Subsequently, dialysis may be of value. There is no specific antidote and treatment is supportive.
Tablets should be stored in well-closed containers.