indication

For use, as an adjunct, in the treatment of pulmonary tuberculosis.

pharmacology

Ethambutol is an oral chemotherapeutic agent which is specifically effective against actively growing microorganisms of the genus Mycobacterium, including M. tuberculosis. Ethambutol inhibits RNA synthesis and decreases tubercle bacilli replication. Nearly all strains of M. tuberculosis and M. kansasii as well as a number of strains of MAC are sensitive to ethambutol.

mechanism of action

Ethambutol inhibits arabinosyl transferases which is involved in cell wall biosynthesis. By inhibiting this enzyme, the bacterial cell wall complex production is inhibited. This leads to an increase in cell wall permeability.

toxicity

The most commonly recognized toxic effect of ethambutol is optic neuropathy, which generally is considered uncommon and reversible in medical literature. Other side effects that have been observed are pruritus, joint pain, gastrointestinal upset, abdominal pain, malaise, headache, dizziness, mental confusion, disorientation, and possible hallucinations.

biotransformation

Hepatic. Up to 15% of administered drug is metabolized to inactive metabolites. The main path of metabolism appears to be an initial oxidation of the alcohol to an aldehydic intermediate, followed by conversion to a dicarboxylic acid.

absorption

About 75% to 80% of an orally administered dose of ethambutol is absorbed from the gastrointestinal tract.

half life

In patients with normal renal function, 3 to 4 hours. In patients with impaired renal function, up to 8 hours.

route of elimination

During the 24-hour period following oral administration of ethambutol hydrochloride approximately 50 percent of the initial dose is excreted unchanged in the urine, while an additional 8 to 15 percent appears in the form of metabolites. From 20 to 22 percent of the initial dose is excreted in the feces as unchanged drug.