Myambutol (ethambutol hydrochloride) is a first-line antimycobacterial agent specifically formulated for the treatment of active tuberculosis. As an integral component of combination therapy, it works by inhibiting the synthesis of arabinogalactan—a critical cell wall component in Mycobacterium tuberculosis. This targeted mechanism of action makes Myambutol essential in preventing resistance development when used alongside other antitubercular drugs like isoniazid, rifampin, and pyrazinamide. Its role is particularly vital in both initial and continuation phases of tuberculosis management, offering clinicians a reliable, well-established option for pulmonary and extrapulmonary TB cases.

Features

• Contains ethambutol hydrochloride as the active pharmaceutical ingredient
• Available in scored, film-coated tablets for accurate dosing (100 mg, 400 mg strengths)
• Exhibits bacteriostatic activity against actively growing tubercle bacilli
• Specifically targets mycobacterial arabinosyl transferase enzymes
• Formulated for optimal oral bioavailability
• Manufactured under strict pharmaceutical quality control standards
• Packaged with desiccant to maintain stability in various climates

Benefits

• Effectively reduces mycobacterial load when used in combination therapy regimens
• Helps prevent development of drug-resistant tuberculosis strains
• Enables shorter, more effective treatment durations compared to historical protocols
• Provides predictable pharmacokinetics with consistent absorption patterns
• Allows for weight-based dosing adjustments to optimize therapeutic outcomes
• Supports treatment adherence through once-daily dosing convenience in most cases

Common use

Myambutol is indicated for the treatment of pulmonary tuberculosis in adults and children when the organism has been shown to be susceptible to, or when susceptibility testing is not available. It must always be used in conjunction with other antituberculosis agents to prevent the emergence of resistant organisms. The drug is particularly valuable in cases where initial resistance to other first-line drugs is suspected or confirmed. Additionally, Myambutol finds application in the treatment of Mycobacterium avium complex (MAC) infections, typically as part of multidrug regimens. Its use extends to both initial intensive phase and continuation phase treatment, depending on the specific therapeutic protocol and resistance patterns.

Dosage and direction

Myambutol dosage must be individualized based on patient weight, renal function, and treatment phase. For adults and children aged 12 years and older with normal renal function, the recommended dosage is 15-25 mg/kg once daily. The higher range (25 mg/kg) is typically used during the initial phase of treatment, while the lower range (15 mg/kg) is employed during the continuation phase.

Administration should occur once daily, preferably at the same time each day, with or without food. Tablets should be swallowed whole with water and not crushed or chewed. For patients with renal impairment, dosage adjustments are mandatory—typically reducing frequency to two or three times per week based on creatinine clearance measurements. Pediatric dosing for children under 12 years follows similar weight-based calculations but requires particular attention to adherence and monitoring.

Treatment duration typically ranges from 6 to 9 months for drug-susceptible tuberculosis, though extended courses may be necessary for drug-resistant cases or extrapulmonary disease. Dosage should never exceed 2.5 grams daily regardless of patient weight.

Precautions

Baseline ophthalmologic examination is mandatory before initiating Myambutol therapy and should be repeated monthly during treatment. Visual acuity and color discrimination testing are particularly crucial as ethambutol can cause optic neuritis. Renal function must be assessed before treatment and monitored periodically, with dosage adjustments for patients with impaired kidney function. Hepatic function should be monitored, though ethambutol is primarily renally excreted.

Patients should be advised to report any visual changes immediately, including blurred vision, constriction of visual fields, or color vision disturbances. Extra caution is warranted in diabetic patients, those with cataracts, and individuals with pre-existing ocular conditions. Regular monitoring of serum uric acid is recommended as ethambutol may cause hyperuricemia. Pregnancy category C status necessitates careful risk-benefit assessment in pregnant women, though tuberculosis itself poses significant fetal risks.

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 the benefits outweigh the risks and no alternatives exist. The drug is contraindicated in patients unable to report visual symptoms reliably, including young children, unconscious patients, and those with significant cognitive impairment. Additionally, Myambutol should not be used as single-agent therapy for any mycobacterial infection due to the high risk of rapid resistance development.

Possible side effect

The most significant adverse reaction associated with Myambutol is optic neuritis, manifesting as decreased visual acuity, scotoma, color blindness, and visual field defects. This effect is generally dose-related and reversible upon discontinuation if detected early. Other ocular effects may include eye pain, photophobia, and retinal hemorrhage.

Common systemic side effects include gastrointestinal disturbances (nausea, abdominal pain, anorexia), hyperuricemia (which may precipitate acute gout in susceptible individuals), and peripheral neuropathy. Less frequently reported effects include dermatitis, pruritus, joint pain, headache, dizziness, and mental confusion. Hepatic enzyme elevations may occur, though significant hepatitis is rare. Hematologic effects such as thrombocytopenia, neutropenia, and eosinophilia have been reported occasionally.

Drug interaction

Myambutol may increase uric acid levels, potentially reducing the effectiveness of uricosuric agents. Aluminum hydroxide-containing antacids may decrease ethambutol absorption when administered concomitantly; doses should be separated by at least 2 hours. While ethambutol has fewer significant interactions than many antituberculosis drugs, caution is advised when co-administering with other neurotoxic agents (including chloroquine, hydroxychloroquine, and some chemotherapy drugs) due to potential additive ocular toxicity.

The drug does not appear to significantly affect cytochrome P450 enzymes, minimizing interactions with many metabolized medications. However, close monitoring is recommended when used with other nephrotoxic agents, as impaired renal excretion may lead to ethambutol accumulation. No clinically significant interactions with antiretroviral drugs have been established, making it generally compatible with HIV treatment regimens.

Missed dose

If a dose of Myambutol is missed, it should be taken as soon as remembered on the same day. However, if it is nearly time for the next scheduled dose, 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. Consistent adherence is critical in tuberculosis treatment to prevent relapse and development of drug resistance. Healthcare providers should be notified of missed doses, particularly if multiple doses are missed, as this may necessitate treatment protocol reassessment.

Overdose

Myambutol overdose may manifest as increased severity of known adverse effects, particularly ocular toxicity. Symptoms may include severe visual disturbances, gastrointestinal upset, dizziness, mental confusion, and possibly peripheral neuropathy. There is no specific antidote for ethambutol overdose. Management involves immediate discontinuation of the drug, gastric lavage if ingestion was recent, and supportive care. Hemodialysis may be effective in removing ethambutol, particularly in patients with impaired renal function. Ophthalmic consultation is mandatory for any suspected overdose, even in the absence of immediate symptoms, as visual changes may develop gradually.

Storage

Myambutol tablets should be stored at controlled room temperature (20-25°C or 68-77°F), protected from light and moisture. Keep the container tightly closed with the desiccant provided. Do not store in bathroom cabinets or other humid locations. Keep out of reach of children and pets. Do not use tablets that show signs of physical deterioration, discoloration, or that are beyond the expiration date printed on the packaging. Proper storage is essential for maintaining drug potency and safety throughout the treatment course.

Disclaimer

This information is provided for educational purposes only and does not constitute medical advice. Myambutol is a prescription medication that must be used under the supervision of a qualified healthcare professional experienced in tuberculosis management. Treatment decisions should be based on individual patient factors, including susceptibility testing when available. Patients should not adjust dosage or discontinue medication without consulting their physician. The manufacturer and prescribing information should be consulted for complete product details, including full prescribing information and potential updates.

Reviews

Clinical studies and decades of use have established Myambutol as a cornerstone of modern tuberculosis treatment. The WHO includes ethambutol in its essential medicines list, reflecting its importance in global TB control. Studies demonstrate that combination regimens containing ethambutol achieve cure rates exceeding 95% in drug-susceptible tuberculosis when adherence is maintained. The drug is generally well-tolerated, with most adverse effects being reversible upon discontinuation. Ophthalmologic monitoring has significantly reduced the incidence of permanent visual impairment, making the risk-benefit profile favorable for most patients. Treatment success rates are particularly high when Myambutol is used as part of directly observed therapy (DOT) programs.