myambutol

Action

Unknown. Thought to interfere with RNA synthesis of bacterial metabolites, decreasing mycobacterial replication.

Availability

Tablets: 100 mg, 400 mg

Indications and dosages

➣ Adjunct in tuberculosis and atypical mycobacterial infection caused by Mycobacterium tuberculosis

Adults and adolescents: In patients who haven't received previous antitubercular therapy, 15 mg/kg P.O. daily. In patients who have received previous antitubercular therapy, 25 mg/kg P.O. daily, decreased after 60 days to 15 mg/kg daily.

Dosage adjustment

• Renal impairment

Contraindications

• Hypersensitivity to drug

Precautions

Use cautiously in:

• impaired renal or hepatic function, cataracts, optic neuritis, recurrent eye inflammation, diabetic retinopathy, gout

• pregnant patients

• children younger than age 13.

Administration

• Obtain specimens for culture and sensitivity testing, as necessary, before starting therapy and periodically throughout therapy.

• Give with food.

Adverse reactions

CNS: confusion, disorientation, malaise, dizziness, hallucinations, headache, peripheral neuritis

EENT: optic neuritis, blurred vision, decreased visual acuity, red-green color blindness, eye pain

GI: nausea, vomiting, abdominal pain, GI upset, anorexia

Hematologic: eosinophilia, thrombocytopenia

Hepatic: transient hepatic impairment

Metabolic: hyperuricemia, hypoglycemia

Musculoskeletal: joint pain, gouty arthritis

Respiratory: bloody sputum, pulmonary infiltrates

Skin: rash, pruritus, toxic epidermal necrolysis

Other: fever, anaphylactoid reactions

Interactions

Drug-drug. Aluminum salts: delayed and reduced ethambutol absorption Other neurotoxic drugs: increased risk of neurotoxicity

Drug-diagnostic tests. Alanine aminotransferase, aspartate aminotransferase, bilirubin, uric acid: increased levels Glucose: decreased level

Patient monitoring

See Watch for serious adverse reactions, such as thrombocytopenia, respiratory problems, and anaphylactoid reactions.

• Monitor liver function tests, CBC, and blood urea nitrogen, creatinine glucose, and serum uric acid levels.

• Give analgesics for drug-induced pain, as prescribed.

• Observe for signs and symptoms of gout.

Patient teaching

• Instruct patient to take with 8 oz of water. If stomach upset occurs, advise him to take with food.

• If patient must take antacids, advise him to take only aluminum-free antacids.

See Tell patient to immediately report easy bruising or bleeding, respiratory problems, or signs and symptoms of hypersensitivity reactions.

• Advise patient to report vision changes and to have annual eye exams. Reassure him that visual disturbances will subside within several weeks to months after drug is discontinued.

• As appropriate, review all other significant and life-threatening adverse reactions and interactions, especially those related to the drugs and tests mentioned above.