ETHAMBUTOL HYDROCHLORIDE

ETHAMBUTOL HYDROCHLORIDE
(e-tham'byoo-tole)
Etibi , Myambutol
Classifications: antituberculosis agent;
Therapeutic:antitubercular

Prototype: Isoniazid
Pregnancy Category: B

Availability

100 mg, 400 mg tablets

Action

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.

Therapeutic Effect

Synthetic antituberculosis agent with bacteriostatic effect. Also effective against atypical mycobacterial infections.

Uses

In conjunction with other antituberculosis agents in treatment of pulmonary tuberculosis.

Unlabeled Uses

Atypical mycobacterial infections.

Contraindications

Optic neuritis; hypersensitivity to ethambutol; optic neuritis, patients unable to report changes in vision (young children, or unconscious patients); children <6 y.

Cautious Use

Renal impairment, hepatic disease; gout; ocular defects (e.g., cataract, recurrent ocular inflammatory conditions, diabetic retinopathy); pregnancy (category B).

Route & Dosage

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 (6–12 y): PO 10–15 mg/kg/d

Administration

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.

Adverse Effects (≥1%)

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).

Interactions

Drug: Aluminum-containing antacids can decrease absorption.

Pharmacokinetics

Absorption: 70–80% 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: In liver. Elimination: 50% in urine within 24 h; 20–22% in feces. Half-Life: 3–4 h.

Nursing Implications

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.
  • 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.

Common adverse effects in italic, life-threatening effects underlined; generic names in bold; classifications in SMALL CAPS; Canadian drug name; Prototype drug

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