ethambutol

Absorption: 80% absorbed following oral administration.

Distribution: Widely distributed to tissues; 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);
Severe hepatic impairment (↓ dose);
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. Perform chest x-ray after 2–3 mo and at end of treatment in patients with negative initial cultures.
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.
Monitor for signs and symptoms of hepatotoxicity (fatigue, nausea, upper abdominal pain, jaundice, scleral icterus, dark urine, clay-colored stools).

Lab Test Considerations:

Monitor renal and hepatic function, CBC, and uric acid levels at baseline and routinely. Frequently ↑ uric acid, which may precipitate an attack of gout.
Obtain acid-fast bacilli smear and culture from sputum monthly until two consecutive specimens are negative.

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.
Do not administer within 4 hr of aluminum hydroxide-containing antacids to prevent ↓ absorption.
PO: Administer with food or milk to minimize GI irritation.
PO: Tablets may be crushed and mixed with apple juice or applesauce.

Patient/Family Teaching ⬆ ⬇

Explain the purpose and side effects of ethambutol. Instruct patient to take as directed without regard to food, but food or milk may prevent GI upset. 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. Advise patient to read Patient Information before starting and with each Rx refill in case of changes.
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 ↓ urine output occurs.
Explain need for continued medical follow-up to assess effectiveness and possible side effects of medication. Periodic lab tests will be needed. Emphasize the importance of routine ophthalmic examinations, especially if signs of optic neuritis occur.
Advise patient to notify health care professional of all Rx or OTC medications, vitamins, or herbal products being taken and to consult with health care professional before taking other medications. Advise patient to avoid aluminum hydroxide-containing antacids within 4 hr of taking ethambutol; may ↓ absorption.
Rep: Advise women of reproductive potential to notify health care professional if pregnancy is planned or suspected or if breastfeeding.

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Pronunciation ⬇

Classifications ⬆ ⬇

Indications ⬆ ⬇

Action ⬆ ⬇

Pharmacokinetics ⬆ ⬇