MYAMBUTOL

What it is

MYAMBUTOL is ethambutol hydrochloride supplied in tablet form, available in 100 mg and 400 mg strengths. MYAMBUTOL is an oral chemotherapeutic agent specifically effective against actively growing Mycobacterium organisms, including Mycobacterium tuberculosis, and appears to inhibit the synthesis of one or more metabolites, causing impairment of cell metabolism, arrest of multiplication, and cell death.

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 initial treatment for patients who have not received previous antituberculosis therapy, MYAMBUTOL should be administered at 15 mg/kg of body weight as a single oral dose once every 24 hours. In re-treatment for patients who have received previous antituberculosis therapy, MYAMBUTOL should be administered at 25 mg/kg of body weight once every 24 hours for the first 60 days, then decreased to 15 mg/kg of body weight once every 24 hours.

Key safety warnings

Severe cutaneous adverse reactions including Stevens-Johnson syndrome, toxic epidermal necrolysis, and drug reaction with eosinophilia and systemic symptoms, which can be life-threatening or fatal, have been reported post-marketing with ethambutol treatment. Patients should be advised of signs and symptoms and monitored closely for skin reactions. If signs and symptoms appear, ethambutol should be withdrawn immediately and an alternative treatment considered. If a patient has developed a serious reaction such as Stevens-Johnson syndrome, toxic epidermal necrolysis or drug reaction with eosinophilia and systemic symptoms with ethambutol use, treatment with ethambutol must not be restarted at any time. MYAMBUTOL may produce decreases in visual acuity due to optic neuritis, which may be related to dose and duration of treatment, with incidence at recommended dosage averaging about 2 to 3% of patients. This effect is generally reversible when the drug is discontinued promptly, though in rare cases recovery may be delayed for up to one year or more and irreversible blindness has been reported. Visual acuity testing 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. Periodic assessment of organ functions, including renal, hepatic and haematopoietic systems, should be made during long-term therapy. Reduction of dosage should be made in patients with decreased renal function since the main path of excretion is by the kidneys.

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 tablets were first registered on the ARTG on 16 February 1994, and MYAMBUTOL 400 mg tablets were first registered on 20 February 2008.