ETHAMBUTOL HYDROCHLORIDE
(e-tham'byoo-tole)
Etibi  , Myambutol
Classifications: antiinfective; antituberculosis agent
Prototype: Isoniazid
Pregnancy Category: B
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100 mg, 400 mg tablets
Mode of action not completely understood, but it appears to inhibit RNA synthesis and thus arrests multiplication of tubercle
bacilli. The emergence of resistant strains is delayed by administering ethambutol in combination with other antituberculosis
drugs.
Synthetic antituberculosis agent with bacteriostatic effect.
In conjunction with at least one other antituberculosis agent in treatment of pulmonary tuberculosis.
Atypical mycobacterial infections.
Optic neuritis; hypersensitivity to ethambutol; optic neuritis, patients unable to report changes in vision (young children,
or unconscious patients); children <6 y.
Renal impairment, hepatic disease; gout; ocular defects (e.g., cataract, recurrent ocular inflammatory conditions, diabetic
retinopathy); pregnancy (category B), lactation.
Tuberculosis
Adult: PO 15 mg/kg q24h; for retreatment start with 25 mg/kg/d for 60 d, then decrease to 15 mg/kg/d
Child: PO
6–12 y, 10–15 mg/kg/d
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Oral
- Give with food if GI irritation occurs.
- Protect ethambutol from light, moisture, and excessive heat. Store at 15°–30° C (59°–86° F)
in tightly closed container unless otherwise directed.
CNS: Headache, dizziness, confusion, hallucinations, paresthesias, joint pains. Special Senses: Ocular toxicity: retrobulbar optic neuritis; possibility of anterior optic neuritis with decrease in visual acuity, temporary loss of vision, constriction of visual fields,
red–green color blindness, central and peripheral scotomas, eye pain, photophobia; retinal hemorrhage and edema. GI: Anorexia, nausea, vomiting, abdominal pain. Body as a Whole: Hypersensitivity (pruritus, dermatitis, anaphylaxis).
Drug:
Aluminum-containing antacids can decrease absorption.
Absorption: 70–80% absorbed from GI tract. Peak: 2–4 h. Distribution: Distributes to most body tissues; highest concentrations in erythrocytes, kidney, lungs, saliva; crosses placenta; distributed
into breast milk. Metabolism: Metabolized in liver. Elimination: 50% excreted in urine within 24 h; 20–22% excreted in feces. Half-Life: 3–4 h.
Assessment & Drug Effects
- Perform C&S prior to and periodically throughout therapy.
- Perform ophthalmoscopic examination prior to and at monthly intervals during therapy. Test eyes separately as well as together.
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Note: Ocular toxicity generally appears within 1–7 mo after start of therapy. Symptoms usually disappear within several weeks
to months after drug is discontinued, depending on degree of ocular damage.
- Monitor I&O ratio in patients with renal impairment. Report oliguria or any significant changes in ratio or in laboratory
reports of kidney function. Systemic accumulation with toxicity can result from delayed drug excretion.
- Lab tests: Perform liver and kidney function tests, CBC, and serum uric acid levels at regular intervals throughout therapy.
Patient & Family Education
- Adhere to drug regimen exactly and keep follow-up appointments.
- Notify physician promptly of the onset of blurred vision, changes in color perception, constriction of visual fields, or any
other visual symptoms. Have eyes checked periodically. Ethambutol can cause irreversible blindness due to optic neuritis.
- Do not breast feed while taking this drug.
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Prototype drug