Myambutol: Targeted Tuberculosis Treatment with Ethambutol HCl
Myambutol
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| Product dosage: 600mg | |||
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| Product dosage: 800mg | |||
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Synonyms | |||
Myambutol, containing the active ingredient ethambutol hydrochloride, is a first-line antimycobacterial agent specifically indicated for the treatment of pulmonary tuberculosis. It is never used as monotherapy but is an essential component of combination regimens, working synergistically with other antitubercular drugs like isoniazid, rifampin, and pyrazinamide. Its primary mechanism of action involves the inhibition of arabinosyl transferase, a crucial enzyme for the synthesis of the mycobacterial cell wall. This targeted action makes it a cornerstone in both the initial intensive phase and continuation phase of tuberculosis management, helping to prevent the emergence of drug-resistant strains and ensuring successful treatment outcomes.
Features
- Active Ingredient: Ethambutol Hydrochloride
- Available Strengths: 100 mg, 400 mg film-coated tablets
- Pharmacologic Class: Synthetic antitubercular agent
- Mechanism of Action: Inhibits arabinosyl transferase enzymes, disrupting arabinogalactan and lipoarabinomannan biosynthesis in the mycobacterial cell wall
- Bioavailability: Approximately 70-80% following oral administration
- Protein Binding: Minimal (20-30%)
- Metabolism: Hepatic; partial conversion to inactive metabolites
- Elimination Half-Life: 3-4 hours (prolonged in renal impairment)
- Excretion: Primarily renal (50% as unchanged drug, 8-15% as metabolites)
- Manufacturing Standards: Produced under current Good Manufacturing Practices (cGMP)
Benefits
- Bacteriostatic Action: Effectively suppresses multiplication of Mycobacterium tuberculosis, particularly actively dividing organisms
- Synergistic Efficacy: Enhances the antibacterial effect of other first-line antitubercular drugs when used in combination therapy
- Resistance Prevention: Critical for preventing the development of drug-resistant tuberculosis strains through multi-drug approach
- Dose-Dependent Activity: Demonstrates concentration-dependent killing against susceptible mycobacteria
- CNS Penetration: Achieves therapeutic concentrations in cerebrospinal fluid, making it suitable for tuberculous meningitis treatment
- Flexible Dosing: Weight-based dosing protocol allows for personalized treatment regimens
Common use
Myambutol is indicated for the treatment of pulmonary tuberculosis in combination with other antituberculous drugs. It is used in both initial treatment phases and retreatment cases. The medication is particularly valuable in geographic areas where isoniazid resistance is known or suspected. It may also be used in the treatment of atypical mycobacterial infections, including Mycobacterium avium complex (MAC), as part of combination regimens, though this represents an off-label use that requires careful clinical consideration.
Dosage and direction
Adult Dosage: The recommended dosage is 15-25 mg/kg body weight administered orally once daily. For initial treatment, the typical dose is 15 mg/kg. For retreatment cases where drug resistance is suspected, the dose may be increased to 25 mg/kg daily for the first two months, then reduced to 15 mg/kg daily.
Pediatric Dosage: Safety and effectiveness in children under 13 years have not been established. For adolescents 13 years and older, use adult dosing recommendations based on body weight.
Administration: Myambutol tablets should be swallowed whole with a full glass of water, preferably at the same time each day to maintain consistent blood levels. Administration with food may minimize gastrointestinal upset, though absorption is not significantly affected. Dosage must be adjusted in patients with renal impairment based on creatinine clearance.
Precautions
Ophthalmic Monitoring: Regular ophthalmologic examinations are mandatory before and during therapy, including tests of visual acuity, color discrimination, and visual fields. Patients should be instructed to report any visual symptoms immediately.
Renal Function: Serum creatinine should be monitored regularly, with dosage adjustments made for patients with impaired renal function. Ethambutol is excreted primarily by the kidneys, and accumulation may occur in renal impairment.
Hepatic Function: Although primarily renally excreted, hepatic function should be monitored as ethambutol is partially metabolized in the liver.
Pregnancy Considerations: Category C - Use during pregnancy only if the potential benefit justifies the potential risk to the fetus. Tuberculosis itself poses significant risks to both mother and fetus.
Pediatric Use: Not recommended for children under 13 years due to difficulty in monitoring visual acuity and color vision.
Geriatric Use: Elderly patients may require dosage adjustments based on renal function and increased susceptibility to ocular toxicity.
Contraindications
- Hypersensitivity to ethambutol or any component of the formulation
- Patients with optic neuritis (unless clinical necessity outweighs risks)
- Patients unable to report visual symptoms or undergo regular ophthalmologic monitoring
- Severe renal impairment with creatinine clearance less than 30 mL/min without appropriate dosage adjustment
- Use in children under 13 years of age
- Patients with pre-existing visual disturbances that would complicate monitoring for ocular toxicity
Possible side effect
Ocular Effects: Retrobulbar neuritis, manifested by decreased visual acuity, scotoma, color blindness, and visual field defects (typically reversible if detected early and medication discontinued)
Gastrointestinal: Abdominal pain, nausea, vomiting, anorexia, and gastrointestinal upset
Dermatological: Dermatitis, pruritus, and photosensitivity reactions
Neurological: Peripheral neuritis, headache, dizziness, confusion, disorientation, and hallucinations
Hepatic: Elevated liver enzymes, hepatitis (rare)
Hematological: Thrombocytopenia, leukopenia, and eosinophilia
Metabolic: Hyperuricemia, precipitation of acute gouty arthritis
Hypersensitivity: Fever, rash, arthralgia, and anaphylactoid reactions
Other: Malaise, joint pain, and numbness or tingling in extremities
Drug interaction
Aluminum Hydroxide: Concomitant administration may decrease ethambutol absorption; separate administration by at least 4 hours
Other Neurotoxic Drugs: May potentiate neurotoxic effects when used with other medications having neurotoxic potential
Antacids: May interfere with absorption; administer at least 2 hours apart
Isoniazid: May increase the risk of neurotoxicity, though the combination is fundamental to tuberculosis treatment
Rifampin: No significant interaction noted; standard combination therapy
Pyrazinamide: No clinically significant interactions reported
Aminoglycosides: Potential additive ototoxic and nephrotoxic effects
Ethanol: May increase the risk of hepatotoxicity
Missed dose
If a dose is missed, it should be taken as soon as remembered unless it is almost time for the next scheduled dose. In that case, the missed dose should be skipped, and the regular dosing schedule resumed. Patients should never double the dose to make up for a missed one. Consistency in dosing is crucial for maintaining therapeutic drug levels and preventing the development of drug resistance. Healthcare providers should be informed about pattern of missed doses to assess adherence issues.
Overdose
Symptoms of overdose may include increased severity of known adverse effects, particularly visual disturbances, gastrointestinal symptoms, and neurological effects. There is no specific antidote for ethambutol overdose. Management includes immediate gastric lavage if ingestion was recent, followed by activated charcoal. Supportive care should be provided, with particular attention to monitoring visual function, renal status, and neurological status. Hemodialysis may enhance elimination of the drug in cases of significant overdose, especially in patients with renal impairment.
Storage
Store at controlled room temperature between 20°C to 25°C (68°F to 77°F). Protect from light and moisture. Keep in the original container with the lid tightly closed. Do not store in bathroom cabinets where humidity levels fluctuate. Keep out of reach of children and pets. Do not use beyond the expiration date printed on the packaging. Proper disposal of unused medication should follow local regulations for pharmaceutical waste.
Disclaimer
This information is provided for educational purposes only and does not constitute medical advice. Healthcare professionals should exercise their own professional judgment when treating patients. Dosage must be individualized based on the patient’s clinical condition, renal function, and response to therapy. Patients should be advised to report any visual changes immediately. The prescribing physician should be familiar with the complete prescribing information before initiating therapy. Treatment of tuberculosis requires careful monitoring and management by physicians experienced in the treatment of mycobacterial diseases.
Reviews
Clinical studies and decades of use have established Myambutol as an essential component of combination therapy for tuberculosis. The drug demonstrates excellent efficacy when used appropriately in multi-drug regimens, with a generally favorable safety profile when monitoring protocols are followed. Ophthalmologic toxicity remains the most significant concern, but with proper monitoring, this risk is manageable. The medication’s role in preventing drug resistance is particularly valued in tuberculosis control programs worldwide. Patient adherence is generally good due to once-daily dosing, though the requirement for regular eye examinations can present challenges in some healthcare settings. Overall, Myambutol continues to be a cornerstone of antituberculosis therapy, with its benefits outweighing risks when used according to established guidelines.