MYAMBUTOL
Clinical safety rating: caution
Comprehensive clinical and safety monograph for MYAMBUTOL (MYAMBUTOL).
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. |
| 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 | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Comprehensive clinical and safety monograph for MYAMBUTOL (MYAMBUTOL).
| Breastfeeding | Ethambutol is excreted into human breast milk in low concentrations; the estimated infant dose is approximately 2-4% of the maternal weight-adjusted dose. The milk-to-plasma ratio is approximately 0.57. The American Academy of Pediatrics considers ethambutol compatible with breastfeeding. Monitor the infant for signs of optic neuritis or gastrointestinal effects. |
| 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. |
■ 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 ethambutol; optic neuritis (unless benefit outweighs risk); children under 13 years of age (relative contraindication).
| Precautions | Optic neuritis (monitor visual acuity and color discrimination); hepatic toxicity; renal impairment (dose adjustment required); interaction with aluminum-containing antacids (decreased absorption). |
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| 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. |