ETHAMBUTOL

What it is

Myambutol is an oral chemotherapeutic agent that is specifically effective against actively growing micro-organisms of the genus Mycobacterium, including Mycobacterium tuberculosis. Myambutol is available as tablets containing ethambutol hydrochloride in strengths of 100 mg and 400 mg.

Approved indications

— Pulmonary tuberculosis. — Primary tuberculosis and extrapulmonary forms of tuberculosis, including miliary tuberculosis, tuberculous meningitis, tuberculosis of bones and joints, genitourinary tuberculosis, tuberculosis of the skin and tuberculous eye diseases.

Dosing overview

Myambutol should not be used as the sole antituberculosis drug, but should be used in conjunction with at least one other antituberculosis drug. Myambutol should be administered on a once every 24-hour basis only. In patients who have not received previous antituberculosis therapy, administer Myambutol 15 mg/kg (7 mg/lb) of body weight, as a single oral dose once every 24 hours. In patients who have received previous antituberculosis therapy, administer Myambutol 25 mg/kg (11 mg/lb) of body weight, as a single oral dose once every 24 hours. After 60 days of Myambutol administration, decrease the dose to 15 mg/kg (7 mg/lb) of body weight and administer as a single oral dose once every 24 hours.

Key safety warnings

Severe cutaneous adverse reactions (SCARs) including Stevens-Johnson syndrome (SJS), toxic epidermal necrolysis (TEN), drug reaction with eosinophilia and systemic symptoms (DRESS), which can be life-threatening or fatal, have been reported post-marketing in association with ethambutol treatment. At the time of prescription patients should be advised of the signs and symptoms and monitored closely for skin reactions. If signs and symptoms suggestive of these reactions appear, ethambutol should be withdrawn immediately and an alternative treatment considered. Myambutol may produce decreases in visual acuity that appear to be due to optic neuritis. This effect may be related to dose and duration of treatment. Incidence with the recommended dosage has averaged about 2 to 3% of patients. This effect is generally reversible when administration of the drug is discontinued promptly. In rare cases, recovery may be delayed for up to one year or more. Irreversible blindness has been reported. Testing of visual acuity should be performed before beginning Myambutol therapy and periodically during drug administration, except that it should be done monthly when a patient is on a dosage of more than 15 mg/kg/day.

Contraindications

Myambutol is contraindicated in patients who are known to be hypersensitive to this drug. It is also contraindicated in patients with known optic neuritis unless clinical judgement determines that it may be used.

Regulatory history

Myambutol 100 mg tablet was first approved on 16 February 1994. Myambutol 400 mg tablet was first approved on 20 February 2008.