Ethambutol (EMB, E) is a medication primarily used to treat tuberculosis. It is usually given in combination with other tuberculosis medications, such as isoniazid, rifampicin and pyrazinamide. It may also be used to treat Mycobacterium avium complex, and Mycobacterium kansasii. It is taken by mouth.

Molecular Structure

Class of Drug

Antituberculosis agent.

Mechanism of Action

Inhibits cell wall synthesis by inhibiting RNA synthesis.

Indications / Dosage / Route

Routes of Administration: Oral only.

Condition: Adjunct in treatment of pulmonary tuberculosis

Dose: Adults, children >13 years: Initial: 15 mg/kg/d.

         Adults: who have received previous antitubercular therapy: 25 mg/kg for 60 days, then 15 mg/kg daily for retreatment if initial treatment fails.

Condition: Combined with other antitubercular drugs

Dose: Adults: 50 mg/kg/d, 3 times/wk

 Note: Ethambutol is administered in combination with the following antituberculosis drugs: isoniazid, rifampin, pyrazinamide. Streptomycin is an alternative to ethambutol in this four-drug regimen.

Adjustment of Dosage

Kidney disease: Creatinine clearance 30-60 mL/min: decrease dosage by 50%; creatinine clearance 10-30 mL/min: decrease dosage by 75%; creatinine clearance <10 mL/min: dose 3 times/wk.

Liver disease: None.

Pediatric: Use with extreme caution in children <6 because of inability to perform visual examinations. May be necessary if infection with multiresistant organism occurs.

Food and Drug Interactions

Food: Take with food to prevent gastric upset.

Pregnancy: Category B.

Lactation: Excreted in breast milk. Considered compatible by American Academy of Pediatrics.

Contraindications: Optic neuritis (relative contraindication), hyper sensitivity to ethambutol.

Warnings / Precautions

> Use with caution in patients with the following conditions: cataracts, inflammatory conditions of the eye, renal disease, gout, diabetic retinopathy.

> In patients with renal insufficiency disease, adjustment is necessary to prevent irreversible eye damage.

Clinically Important Drug Interactions

> Ethambutol increases effects/toxicity of drugs that produce neurotoxicity.

Adverse Reactions

> Common: headache, hyperuricemia, nausea.

> Serious: thrombocytopenia, anaphylactic reactions, disorientation, optic neuritis, peripheral neuritis, increased Ever enzymes, pulmonary infiltrates, eosinophilia.

Parameters to Monitor

> CBC with differential and platelets, liver enzymes.

> Culture organisms for sensitivity testing before and periodically during therapy. Be aware that drug resistance may develop.

> Symptoms of visual disturbances: changes in color discrimination (red/green color blindness), blurred vision. Discontinue if these occur, particularly when there are changes in color perception. If visual impairment occurs and is not identified, continued treatment with ethambutol may lead to permanent blindness.

> Signs and symptoms of hepatotoxicity.

> Signs of hyperuricemia.

Advice to Patient

> Do not discontinue drug without approval.

Further Useful Info

> Ethambutol is not to be used as the sole therapy for tuberculosis as resistance can develop rapidly.

> Frequent testing of visual acuity for each eye is required during therapy with ethambutol. Employment of Snellen charts for all patients is suggested. Visual acuity changes are noted with these tests. Ethambutol should be discontinued and patient reevaluated at frequent intervals.

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