Ethambutol Hydrochloride Side Effects

ADVERSE REACTIONS Ethambutol hydrochloride 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 in 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 hydrochloride 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.

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 hydrochloride.

The following table may be useful in interpreting possible changes in visual acuity attributable to ethambutol hydrochloride.

Initial Snellen Reading Reading Indicating Significant Decrease Significant Number of Lines Decrease Number of Points 20/13 20/25 3 12 20/15 0/25 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 20/40 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.