Myambutol (ethambutol hydrochloride) is a first-line bacteriostatic antimycobacterial agent specifically formulated for the treatment of active tuberculosis. As an essential component of combination therapy regimens, it demonstrates selective activity against Mycobacterium tuberculosis by inhibiting arabinosyl transferase enzymes critical for mycobacterial cell wall synthesis. This mechanism provides clinicians with a potent therapeutic tool that complements other antituberculosis medications, reducing treatment duration and minimizing resistance development. The drug’s established safety profile and predictable pharmacokinetics make it a cornerstone in both initial and continuation phases of tuberculosis management worldwide.

Features

• Contains ethambutol hydrochloride as active pharmaceutical ingredient
• Available in 100 mg, 200 mg, 400 mg, and 800 mg film-coated tablets
• Exhibits selective activity against actively dividing mycobacteria
• Demonstrated bioavailability of approximately 75-80% following oral administration
• Plasma protein binding limited to 20-30%
• Primarily renal elimination with half-life of 3-4 hours in patients with normal renal function
• Stable at room temperature with shelf life of 36 months from manufacturing date

Benefits

• Prevents emergence of drug-resistant tuberculosis strains when used in combination therapy
• Enables shorter treatment durations compared to historical monotherapy approaches
• Reduces bacterial load in pulmonary and extrapulmonary tuberculosis infections
• Maintains therapeutic efficacy while minimizing cross-resistance concerns
• Provides flexible dosing options adaptable to patient-specific factors
• Supports directly observed therapy (DOT) protocols through once-daily dosing

Common use

Myambutol is indicated for the treatment of active pulmonary tuberculosis in combination with other antituberculosis drugs such as isoniazid, rifampin, and pyrazinamide. It is employed in both the initial intensive phase and continuation phase of treatment according to established guidelines from the World Health Organization and Centers for Disease Control and Prevention. The medication is also utilized in certain cases of Mycobacterium avium complex (MAC) infections, particularly in HIV-positive patients, though this represents an off-label application. Clinical use follows standardized protocols based on drug susceptibility testing results and patient presentation characteristics.

Dosage and direction

The recommended dosage of Myambutol is weight-based and administered once daily. For adults and children aged 12 years and older: 15-25 mg/kg (maximum 2.5 grams) daily as part of combination therapy. Specific dosing guidelines include: 15 mg/kg for patients receiving daily therapy throughout treatment; 25 mg/kg (maximum 2.5 grams) for patients receiving twice-weekly therapy; and 50 mg/kg (maximum 2.5 grams) for patients receiving thrice-weekly therapy. Pediatric dosing for children under 12 years: 15-20 mg/kg daily (maximum 1 gram). Administration should occur with or without food, though consistency in timing relative to meals is recommended to maintain stable absorption patterns. Tablets should be swallowed whole with water and not crushed or chewed.

Precautions

Baseline ophthalmological examination is mandatory before initiating therapy and should be repeated monthly during treatment. Visual acuity and color discrimination testing are essential monitoring parameters. Renal function must be assessed before treatment and periodically during therapy, with dosage adjustments required for patients with creatinine clearance below 30 mL/min. Hepatic function should be monitored regularly due to potential hepatotoxicity concerns. Patients should be educated to report any visual changes immediately, including blurred vision, constricted visual fields, or color vision disturbances. Use with caution in patients with pre-existing ocular conditions such as cataracts, diabetic retinopathy, or optic neuritis. Regular assessment of uric acid levels is recommended due to potential hyperuricemia.

Contraindications

Myambutol is contraindicated in patients with known hypersensitivity to ethambutol or any component of the formulation. It must not be administered to patients with optic neuritis unless no alternative therapeutic options exist and potential benefits outweigh risks. The drug is contraindicated in children too young to undergo reliable visual acuity testing (generally under 5 years). Additional contraindications include severe renal impairment (creatinine clearance <30 mL/min) without appropriate dosage adjustment and patients with uncontrolled gout or history of ethambutol-induced hyperuricemia with complications.

Possible side effect

Ocular effects represent the most significant adverse reactions, including optic neuritis (manifesting as decreased visual acuity, scotomas, color blindness), and rarely, retinal hemorrhage. Gastrointestinal disturbances may occur, such as nausea, vomiting, abdominal pain, and anorexia. Dermatological reactions include rash, pruritus, and dermatitis. Neurological effects may present as headache, dizziness, confusion, and peripheral neuritis. Metabolic disturbances include hyperuricemia, occasional gouty arthritis, and transient liver enzyme elevations. Hematological changes such as leukopenia, thrombocytopenia, and eosinophilia have been reported. Miscellaneous reactions include fever, malaise, and joint pain.

Drug interaction

Concurrent administration with aluminum hydroxide-containing antacids may decrease ethambutol absorption; separate administration by at least 2 hours. Neurotoxic medications such as chloroquine, hydroxychloroquine, or cisplatin may potentiate neurological side effects. Concomitant use with other antituberculosis drugs may increase hepatotoxicity risk. Ethambutol may decrease renal excretion of uric acid, potentially interfering with uricosuric agents. The drug may enhance the toxicity of other medications causing ocular damage. No significant interactions with cytochrome P450 enzymes have been documented, though monitoring is advised with narrow therapeutic index medications.

Missed dose

If a dose is missed, it should be taken as soon as remembered unless it is nearly time for the next scheduled dose. In such cases, the missed dose should be skipped and the regular dosing schedule resumed. Patients should never double the dose to make up for a missed administration. Consistency in dosing is critical for maintaining therapeutic drug levels and preventing resistance development. Healthcare providers should be notified of missed doses, particularly in directly observed therapy programs, to ensure appropriate management and documentation.

Overdose

Symptoms of overdose may include exaggerated pharmacological effects and adverse reactions, particularly visual disturbances, gastrointestinal upset, dizziness, confusion, and metabolic acidosis. Management involves immediate gastric lavage or activated charcoal if ingestion occurred within 2 hours. Supportive care includes maintenance of hydration, electrolyte balance, and monitoring of visual function, renal parameters, and hepatic indices. No specific antidote exists; hemodialysis may enhance elimination in cases of severe overdose, particularly in patients with renal impairment. Ophthalmological consultation is mandatory for any suspected overdose situation.

Storage

Store at controlled room temperature between 20-25°C (68-77°F), with excursions permitted between 15-30°C (59-86°F). Protect from light and moisture. Keep container tightly closed and store in original packaging. Do not remove desiccant from bottle. Keep out of reach of children and pets. Do not use beyond the expiration date printed on packaging. Properly dispose of unused medication through take-back programs or according to local regulations.

Disclaimer

This information is provided for educational purposes only and does not constitute medical advice. Treatment decisions must be made by qualified healthcare professionals based on individual patient circumstances. The prescribing physician should be consulted for complete prescribing information, including boxed warnings regarding ocular toxicity. Medication should only be used under appropriate medical supervision with regular monitoring. Patients should not adjust dosage or discontinue medication without medical guidance.

Reviews

Clinical studies demonstrate Myambutol’s efficacy in combination therapy regimens, with success rates exceeding 95% in drug-susceptible tuberculosis when administered according to guidelines. The WHO Essential Medicines List includes ethambutol as a core antituberculosis agent. Systematic reviews confirm its role in reducing treatment duration and preventing resistance development. Ophthalmological monitoring remains the critical component for safe administration, with visual toxicity occurring in approximately 1-2% of patients receiving recommended doses, typically reversible upon discontinuation when detected early. The drug’s favorable drug interaction profile makes it suitable for complex medication regimens in comorbid patients.