Ethambutol Hydrochloride (2 brand names, 1 dosage form, 1 route)
Available dosage forms: TABLET.
Routes of administration: ORAL.
Brand Names
- ETHAMBUTOL HYDROCHLORIDE
- MYAMBUTOL
Indications and Usage
ETHAMBUTOL HCl is indicated for the treatment of pulmonary tuberculosis. It should not be used as the sole antituberculous drug, but should be used in conjunction with at least one other antituberculous drug. Selection of the companion drug should be based on clinical experience, considerations of comparative safety, and appropriate in vitro susceptibility studies. In patients who have not received previous antituberculous therapy, ie, initial treatment, the most frequently used regimens have been the following: ETHAMBUTOL HCl plus isoniazidETHAMBUTOL HCl plus isoniazid plus streptomycin. In patients who have received previous antituberculous therapy, mycobacterial resistance to other drugs used in initial therapy is frequent. Consequently, in such retreatment patients, ETHAMBUTOL HCl should be combined with at least one of the second line drugs not previously administered to the patient and to which bacterial susceptibility has been indicated by appropriate in vitro studies. Antituberculous drugs used with ETHAMBUTOL HCl have included cycloserine, ethionamide, pyrazinamide, viomycin and other drugs. Isoniazid, aminosalicylic acid, and streptomycin have also been used in multiple drug regimens. Alternating drug regimens have also been utilized.
Dosage and Administration
ETHAMBUTOL HCl should not be used alone, in initial treatment or in tretreatment. ETHAMBUTOL HCl should be administered on a once every 24-hour basis only. Absorption is not significantly altered by administration with food. Therapy, in general, should be continued until bacteriological conversion has become permanent and maximal clinical improvement has occurred. ETHAMBUTOL HCl is not recommended for use in pediatric patients under thirteen years of age since safe conditions for use have not been established.
Contraindications
ETHAMBUTOL HCl 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 judgment determines that it may be used. ETHAMBUTOL HCl is contraindicated in patients who are unable to appreciate and report visual side effects or changes in vision (e.g., young children, unconscious patients).
Adverse Reactions
ETHAMBUTOL HCl may produce decreases in visual acuity, including irreversible blindness, which appear to be due to optic neuritis. Optic neuropathy including optic neuritis or retrobulbar neuritis occurring in association with ethambutol therapy may be characterized by one or more of the following events: decreased visual acuity, scotoma, color blindness, and/or visual defect. These events have also been reported in the absence of a diagnosis of optic or retrobulbar neuritis. Patients should be advised to report promptly to their physician any change of visual acuity. The change in visual acuity may be unilateral or bilateral and hence each eye must be tested separately and both eyes tested together. Testing of visual acuity should be performed before beginning ETHAMBUTOL HCl 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 per kilogram per day. Snellen eye charts are recommended for testing of visual acuity. Studies have shown that there are definite fluctuations of one or two lines of the Snellen chart in the visual acuity of many tuberculous patients not receiving ETHAMBUTOL HCl. The following table may be useful in interpreting possible changes in visual acuity attributable to ETHAMBUTOL HCl. Initial Reading Significant Decreased Snellen Indicating Number Number Reading Significant of Lines of Points Decrease 20/13 20/25 3 12 20/15 20/25 2 10 20/20 20/30 2 10 20/25 20/40 2 15 20/30 20/50 2 20 20/40 20/70 2 30 20/50 20/70 1 20 In general, changes in visual acuity less than those indicated under “Significant Number of Lines” and “Decrease Number of Points” may be due to chance variation, limitations of the testing method, or physiologic variability. Conversely, changes in visual acuity equaling or exceeding those under “Significant Number of Lines” and “Decrease Number of Points” indicate need for retesting and careful evaluation of the patient’s visual status. If careful ev
Drug Interactions
The results of a study of coadministration of ETHAMBUTOL HCl (50mg/kg) with an aluminum hydroxide containing antacid to 13 patients with tuberculosis showed a reduction of mean serum concentrations and urinary excretion of ethambutol of approximately 20% and 13%, respectively, suggesting that the oral absorption of ethambutol may be reduced by these antacid products. It is recommended to avoid concurrent administration of ethambutol with aluminum hydroxide containing antacids for at least 4 hours following ethambutol administration.