Dosing and uses of Myambutol (ethambutol)
Adult dosage forms and strengths
tablet
- 100mg
- 400mg
Tuberculosis
Prescribing information
- Initial TB treatment: 15 mg/kg PO qDay
- Prior TB treatment: 25 mg/kg PO qDay; after 60 days, decrease to 15 mg/kg PO qDay
Daily administration
- Guidelines from American Thoracic Society (ATS), Centers for Disease Control and Prevention (CDC), and the Infectious Diseases Society of America (IDSA)
- 40-55 kg: 800 mg PO
- 56-75 kg: 1.2 g PO
- >75 kg: 1.6 g PO
Twice weekly administration
- Guidelines from American Thoracic Society (ATS), Centers for Disease Control and Prevention (CDC), and the Infectious Diseases Society of America (IDSA)
- 40-55 kg: 2 g PO
- 56-75 kg: 2.8 g PO
- >75 kg: 4 g PO
3x per week administration
- Guidelines from American Thoracic Society (ATS), Centers for Disease Control and Prevention (CDC), and the Infectious Diseases Society of America (IDSA)
- 40-55 kg: 1.2 g PO
- 56-75 kg: 2 g PO
- >75 kg: 2.4 g PO
Disseminated MAC (Off-label)
Treatment: 15 mg/kg PO qd
Prophylaxis: use same dose with other antibiotics
Pulmonary M. Avium Complex (MAC) without HIV (Off-label)
25 mg/kg PO qD; after 60 d, decrease to 15 mg/kg PO qd
Other Indications & Uses
Tuberculosis: intended to be used concomitantly with other anti-TB drugs; usually isoniazid initially; subsequently, use second-line anti-TB drugs
Off-label: MAC infections
Pediatric dosage forms and strengths
tablet
- 100mg
- 400mg
Tuberculosis
Prescribing information
- Use not recommended in patients <13 years, but has been used in peds
ATS, CDC, and IDSA
- Guidelines from American Thoracic Society (ATS), Centers for Disease Control and Prevention (CDC), and the Infectious Diseases Society of America (IDSA)
- 15-20 mg/kg/day PO; not to exceed 1 g/day OR
- 50 mg/kg PO 2x/week; not to exceed 2.5 g/dose
AAp
- Guidelines from the American Academy of Pediatrics (AAP)
- 15-25 mg/kg/day PO; not to exceed 1 g/day OR
- 50 mg/kg PO 2x/week; not to exceed 2.5 g/dose
Disseminated MAC, Prophylaxis (Off-label)
As adult, 15 mg/kg PO qDay combined with other drugs; not to exceed 1 g/day
Myambutol (ethambutol) adverse (side) effects
Frequency not defined
Acute gout or hyperuricemia
Abdominal pain
Anaphylaxis
Anorexia
Confusion, disorientation
Fever
Headache
LFT abnormalities
Malaise
Nausea
Optic neuritis; symptoms may include decreased acuity, color blindness or visual defects (usually revrsible with discontinuation, though irreversible blindness has been reported)
Peripheral neuritis
Pruritis
Rash
Vomiting
Warnings
Contraindications
Optic neuritis
Hypersensitivity
Cautions
See pkg insert for complete dosage info
< 5 yo: may be difficult to monitor visual acuity
Pregnancy and lactation
Pregnancy category: B
Lactation: enters breast milk; use with caution (AAP Committee states "compatible with nursing")
Pregnancy categories
A: Generally acceptable. Controlled studies in pregnant women show no evidence of fetal risk.
B: May be acceptable. Either animal studies show no risk but human studies not available or animal studies showed minor risks and human studies done and showed no risk.
C: Use with caution if benefits outweigh risks. Animal studies show risk and human studies not available or neither animal nor human studies done.
D: Use in LIFE-THREATENING emergencies when no safer drug available. Positive evidence of human fetal risk.
X: Do not use in pregnancy. Risks involved outweigh potential benefits. Safer alternatives exist.
NA: Information not available.
Pharmacology of Myambutol (ethambutol)
Mechanism of action
Interferes with metabolite production in Mycobacterium
Absorption
Bioavailability: ~80%
Peak Plasma Time: 2-4 hr
Distribution
Widely throughout body; concentrated in kidneys, lungs, saliva, and red blood cells
Relative diffusion from blood into CSF: Adequate with or without inflammation (exceeds usual MICs)
CSF:blood level ratio: 0% (normal meninges); 25% (inflamed meninges)
Protein binding: 20-30%
Metabolism
Hepatic (20%) to inactive metabolite
Elimination
Half-life elimination: 2.5-3.6 hr; 7-15 hr (end-stage renal disease)
Excretion: ~50% urine; ~20% feces as unchanged drug
