MYAMBUTOL
Clinical safety rating
cautionComprehensive clinical and safety monograph for MYAMBUTOL (MYAMBUTOL).
Comprehensive clinical and safety monograph for MYAMBUTOL (MYAMBUTOL).
Treatment of pulmonary tuberculosis in combination with other antituberculosis agentsTreatment of extrapulmonary tuberculosis
Visual impairment, Color blindness
Inhibits arabinosyl transferase, an enzyme involved in cell wall synthesis of mycobacteria, leading to inhibition of cell growth.
| Metabolism | Partially metabolized in the liver via dealkylation to an aldehyde intermediate, which is further oxidized to a dicarboxylic acid. Approximately 50% of the drug is excreted unchanged in urine. |
| Excretion | Renal: 50% unchanged drug; 20% as metabolite (ethambutol carboxylic acid); 15% as aldehyde intermediate; 15% unknown; fecal: <10%. |
| Half-life | Terminal elimination half-life: 3-4 hours in normal renal function; prolonged to 7-15 hours in renal impairment. |
| Protein binding | 20-30% bound to albumin. |
| Volume of Distribution | 1.6 L/kg; distributes widely into tissues, including erythrocytes and cerebrospinal fluid (with inflamed meninges). |
| Bioavailability | Oral: approximately 80% absorbed. |
| Onset of Action | Oral: 1-2 hours (bacteriostatic effect); ocular toxicity onset: weeks to months. |
| Duration of Action | Oral: 24 hours (bacteriostatic); for tuberculosis therapy, continue for 2 months initial phase. |
| Molecular Weight | 204.31 |
| Action Class | Mycobacterial cell wall inhibitors-Ethambutol |
| Brand Substitutes | ALBUTOL 800MG TABLET, Tibitol 800mg Tablet, Cure E 800mg Tablet, Anbutol 800mg Tablet, Sunibutol 800mg Tablet, ALBUTOL 200MG TABLET, CAVIBUTOL 200MG TABLET, Themibutol 200mg Tablet, ZYTHAM 200MG TABLET, Combutol 200 Tablet |
15-25 mg/kg orally once daily (max 2.5 g/day); usual dose 20 mg/kg/day.
| Dosage form | TABLET |
| Renal impairment | CrCl 30-60 mL/min: 15-20 mg/kg daily; CrCl 10-29 mL/min: 15 mg/kg every 24-36 hours; CrCl <10 mL/min: 15 mg/kg every 48 hours. |
| Liver impairment | No specific Child-Pugh based adjustments; use with caution in severe hepatic impairment. |
| Pediatric use | 15-25 mg/kg orally once daily (max 1 g/day for children weighing <20 kg, otherwise 2.5 g/day). |
| Geriatric use | Consider reduced initial dose based on renal function; monitor for optic neuritis. |
| 1st trimester | Contraindicated based on documented teratogenicity. |
| 2nd trimester | Contraindicated; known risk of fetal harm (optic neuritis). |
| 3rd trimester | Contraindicated; risk of ocular toxicity in neonate. |
Clinical note
Comprehensive clinical and safety monograph for MYAMBUTOL (MYAMBUTOL).
| Placental transfer | Crosses placenta; fetal serum concentrations approximate maternal levels. |
| Breastfeeding | Excreted into breast milk in small amounts; potential for optic toxicity in infant; discontinue nursing or discontinue drug. |
| Lactation Rating | L3 (moderately safe) |
| Teratogenic Risk | Ethambutol (Myambutol) is classified as FDA Pregnancy Category B. Animal studies have not demonstrated teratogenic effects. Human data are limited but do not suggest a significant increase in major malformations. However, due to the risk of optic neuritis in the mother, use during pregnancy should be cautious and only if clearly needed. |
| Fetal Monitoring | Baseline and monthly visual acuity and color vision tests for the mother due to risk of optic neuritis. Liver function tests and renal function tests. In pregnancy, consider fetal ultrasound to monitor growth. Also monitor for signs of peripheral neuropathy. |
| Fertility Effects | No known specific adverse effects on fertility in humans. Animal studies have not shown impairment of fertility. |
■ FDA Black Box Warning
MYAMBUTOL may cause optic neuritis and decreased visual acuity, which may be dose-related and reversible upon discontinuation. Not recommended for use in children under 13 years of age.
| Serious Effects |
Hypersensitivity to ethambutolOptic neuritisPre-existing optic neuropathySevere renal impairment (CrCl <10 mL/min)
| Precautions | Optic neuritis (monitor visual acuity and color discrimination); hepatic toxicity; renal impairment (dose adjustment required); interaction with aluminum-containing antacids (decreased absorption). |
| Food/Dietary | No significant food interactions. However, administration with food may reduce gastrointestinal upset. Concurrent use with aluminum-containing antacids may decrease absorption; separate by at least 2 hours. |
| Clinical Pearls | MYAMBUTOL (ethambutol) is a bacteriostatic agent used primarily in combination therapy for tuberculosis. Monitor for optic neuritis, which can cause decreased visual acuity, color blindness, and visual field defects; baseline and monthly visual acuity and color discrimination tests are mandatory. Dose adjustments required in renal impairment (CrCl <30 mL/min). Avoid in children <13 years old due to inability to monitor vision. May cause hyperuricemia; monitor uric acid levels in patients with gout. |
| Patient Advice | Take exactly as prescribed, usually once daily, with or without food. · Report any changes in vision immediately, such as blurred vision, difficulty seeing colors, or blind spots. · Avoid consuming alcohol; may increase risk of liver toxicity. · Do not stop taking this medication even if you feel better; complete full course to prevent resistance. · This drug may cause numbness or tingling in hands or feet; report these symptoms. · Inform your doctor if you have kidney disease, gout, or eye problems before starting treatment. |
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