ethambutol

Absorption: Rapidly and well absorbed (80%) from the GI tract.

Distribution: Widely distributed; crosses blood-brain barrier in small amounts.

Metabolism/Excretion: 50% metabolized by the liver, 50% eliminated unchanged by the kidneys.

Half-Life: 3.3 hr (↑ in renal or hepatic impairment).

Time/Action Profile ⬆ ⬇

(plasma concentrations)

ROUTE	ONSET	PEAK	DURATION
PO	rapid	2–4 hr	24 hr

Contraind./Precautions ⬆ ⬇

Contraindicated in:

Hypersensitivity;
Optic neuritis.

Use Cautiously in:

Renal impairment (dose ↓ required);
Severe hepatic impairment (dose ↓ required);
OB: Although safety not established, ethambutol has been used with isoniazid in pregnant women without fetal adverse effects;
Lactation: Use while breastfeeding only if potential maternal benefit justifies potential risk to infant.

Adv. Reactions/Side Effects ⬆ ⬇

EENT: optic neuritis

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

Metab: hyperuricemia

MS: joint pain

Neuro: confusion, dizziness, hallucinations, headache, malaise, peripheral neuritis

Resp: pulmonary infiltrates

Misc: anaphylactoid reactions, fever

Interactions ⬆ ⬇

Drug-drug:

Neurotoxicity may be ↑ with other neurotoxic agents.
Aluminum hydroxide may ↓ absorption (space doses 4 hr apart).

Route/Dosage ⬆ ⬇

PO (Adults and Children >13 yr): 15–25 mg/kg/day (max = 2.5 g/day) or 50 mg/kg (up to 2.5 g) twice weekly or 25–30 mg/kg (up to 2.5 g) 3 times weekly.
PO (Children 1 mo–13 yr): HIV negative: 15–20 mg/kg/day once daily (max = 1 g/day) or 50 mg/kg/dose twice weekly (max = 2.5 g/dose); HIV-exposed/-infected: 15–25 mg/kg/day once daily (max = 2.5 g/day); MAC, secondary prophylaxis, or treatment in HIV-exposed/-infected: 15–25 mg/kg/day once daily (max = 2.5 g/day) with clarithromycin (or azithromycin) with or without rifabutin; Nontuberculous mycobacterial infection: 15–25 mg/kg/day once daily (max = 2.5 g/day).

Availability ⬆ ⬇

(Generic available)

Tablets: 100 mg; 400 mg

Assessment ⬆ ⬇

Mycobacterial studies and susceptibility tests should be performed before and periodically during therapy to detect possible resistance.
Assess lung sounds and character and amount of sputum periodically during therapy.
Assessments of visual function should be made frequently during therapy. Advise patient to report blurring of vision, constriction of visual fields, or changes in color perception immediately. Visual impairment, if not identified early, may lead to permanent sight impairment.

Lab Test Considerations:

Monitor renal and hepatic functions, CBC, and uric acid levels routinely. Frequently causes elevated uric acid concentrations, which may precipitate an attack of gout.

Implementation ⬆ ⬇

Ethambutol is given as a single daily dose and should be taken at the same time each day. Some regimens require dosing 2–3 times/wk. Usually administered concurrently with other antitubercular medications to prevent development of bacterial resistance.
PO: Administer with food or milk to minimize GI irritation.
PO: Tablets may be crushed and mixed with apple juice or apple sauce.

Patient/Family Teaching ⬆ ⬇

Instruct patient to take medication as directed. Take missed doses as soon as possible unless almost time for next dose; do not double up on missed doses. A full course of therapy may take mo to yr. Do not discontinue without consulting health care professional, even though symptoms may disappear.
Instruct patient to notify health care professional if no improvement is seen in 2–3 wk. Health care professional should also be notified if unexpected weight gain or decreased urine output occurs.
Emphasize the importance of routine exams to evaluate progress and ophthalmic examinations if signs of optic neuritis occur.
Rep: Advise females of reproductive potential to notify health care professional if pregnancy is planned or suspected or if breastfeeding.

Evaluation/Desired Outcomes ⬆ ⬇

Resolution of clinical symptoms of tuberculosis.
- Decrease in acid-fast bacteria in sputum samples.
- Improvement seen in chest x rays. Therapy for tuberculosis is usually continued for at least 1–2 yr.

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Pronunciation ⬇

Classifications ⬆ ⬇

Indications ⬆ ⬇

Action ⬆ ⬇

Pharmacokinetics ⬆ ⬇