What it's for (Indications)
- Ethambutol + Isoniazid + Rifampicin (EHR), such as in the example brand Myrin, is a fixed-dose combination medication primarily indicated for the treatment of active tuberculosis (TB).
- This encompasses both pulmonary and extrapulmonary forms of the disease caused by susceptible strains of Mycobacterium tuberculosis.
- It is a cornerstone of first-line anti-tubercular regimens, particularly in the intensive phase, to achieve rapid bacterial killing and prevent the emergence of drug resistance.
- Its use is guided by national and international treatment protocols, often in conjunction with other anti-TB agents like pyrazinamide, based on the patient's specific clinical presentation, prior treatment history, and local resistance patterns.
- The combination simplifies treatment regimens, potentially improving patient adherence and outcomes in the complex management of tuberculosis.
Dosage Information
| Type | Guideline |
|---|---|
| Standard | The dosage of Ethambutol + Isoniazid + Rifampicin must be individualized based on the patient's body weight and the specific treatment phase (intensive or continuation) as per established guidelines from organizations such as the World Health Organization (WHO) or national TB programs. This fixed-dose combination is typically administered orally, once daily, preferably on an empty stomach to optimize absorption of rifampicin. Specific strengths are available to facilitate weight-band dosing; for instance, a common regimen might involve dosages designed to deliver approximately 15 mg/kg of ethambutol, 5 mg/kg of isoniazid, and 10 mg/kg of rifampicin per day. Dosage adjustments are critical in patients with significant renal or hepatic impairment, and in pediatric populations. Adherence to the prescribed regimen for the full duration is paramount to prevent treatment failure and the development of drug-resistant tuberculosis. Healthcare professionals must refer to the most current guidelines and product-specific information for precise dosing instructions. |
Safety & Warnings
Common Side Effects
- Treatment with Ethambutol + Isoniazid + Rifampicin can be associated with a range of side effects, some of which can be serious.
- Common side effects include gastrointestinal disturbances (nausea, vomiting, abdominal pain), rash, fever, and flu-like symptoms.
- Rifampicin is known to cause orange-red discoloration of urine, tears, sweat, and other body fluids, which is harmless but can stain contact lenses.
- More serious adverse effects warranting immediate medical attention include hepatotoxicity, manifesting as elevated liver enzymes, jaundice, dark urine, or fatigue, primarily due to isoniazid and rifampicin.
- Isoniazid can also cause peripheral neuropathy, which may be ameliorated by pyridoxine (Vitamin B6) supplementation.
- Ethambutol is notably associated with optic neuritis, potentially leading to dose-related, irreversible vision loss, characterized by blurred vision, color blindness (especially red-green), or visual field defects.
- Other potential side effects include arthralgia, hyperuricemia, thrombocytopenia, hemolytic anemia, and drug interactions, particularly with rifampicin.
- Patients should be thoroughly counseled on potential side effects and advised to report any concerning symptoms promptly.
Serious Warnings
- Black Box Warning: SEVERE HEPATOTOXICITY AND OPTIC NEURITIS: This fixed-dose combination drug carries a significant risk of severe, and potentially fatal, hepatotoxicity primarily due to the isoniazid and rifampicin components. Cases of severe and sometimes fatal hepatitis have been reported, even after many months of treatment. Patients must be carefully monitored for signs and symptoms of liver injury, including fatigue, malaise, anorexia, nausea, vomiting, dark urine, or jaundice, and liver function tests (e.g., AST, ALT, bilirubin) should be performed at baseline and monitored regularly throughout therapy. The risk of hepatotoxicity is increased in individuals with pre-existing liver disease, chronic alcohol use, or advanced age. Furthermore, the ethambutol component is associated with optic neuritis, which can lead to progressive and irreversible visual loss, including blindness. Baseline and regular ophthalmological examinations, including visual acuity and color discrimination tests, are mandatory during treatment. Patients unable to report visual symptoms reliably (e.g., young children) should not receive ethambutol. Prompt discontinuation of the drug is required upon evidence of significant hepatotoxicity or visual impairment. Due to the high potential for serious adverse reactions, this medication should only be prescribed by healthcare professionals experienced in the treatment of tuberculosis and capable of monitoring for and managing these severe risks.
- Ethambutol + Isoniazid + Rifampicin requires careful monitoring due to several significant safety concerns.
- Severe and sometimes fatal hepatotoxicity is a major risk, particularly with isoniazid and rifampicin, necessitating baseline and periodic monitoring of liver function tests throughout treatment.
- Patients should be advised to avoid alcohol, as it increases the risk of liver injury.
- Ethambutol carries a significant risk of optic neuritis, which can lead to permanent visual impairment.
- Baseline and regular ophthalmological examinations, including visual acuity and color discrimination tests, are crucial, especially for patients on high doses, prolonged therapy, or those with pre-existing visual conditions.
- The drug should generally not be used in children too young to undergo reliable visual acuity testing.
- Isoniazid can cause peripheral neuropathy; co-administration of pyridoxine (Vitamin B6) is often recommended, especially in malnourished patients, diabetics, alcoholics, or those predisposed to neuropathy.
- Rifampicin is a potent inducer of hepatic cytochrome P450 enzymes, leading to numerous significant drug interactions, which can reduce the efficacy of co-administered medications such as oral contraceptives, anticoagulants, antiretrovirals, and corticosteroids.
- Patients must be carefully evaluated for potential drug interactions.
- Dose adjustments may be necessary in patients with renal impairment.
- Hyperuricemia and exacerbation of gout are possible due to ethambutol.
- Close clinical supervision is essential throughout the entire course of therapy.
How it Works (Mechanism of Action)
The therapeutic efficacy of Ethambutol + Isoniazid + Rifampicin stems from the synergistic action of its three distinct anti-mycobacterial agents, each targeting a different essential process in Mycobacterium tuberculosis. Isoniazid (INH) is a pro-drug activated by the mycobacterial catalase-peroxidase enzyme (KatG), which then inhibits the synthesis of mycolic acid, a crucial component of the mycobacterial cell wall. This action is primarily bactericidal against actively growing bacilli. Rifampicin inhibits DNA-dependent RNA polymerase in prokaryotic cells, thereby preventing the synthesis of RNA and subsequent protein synthesis, leading to rapid bactericidal action against both intracellular and extracellular mycobacteria. Ethambutol inhibits arabinosyl transferase, an enzyme involved in the polymerization of arabinogalactan, a component of the mycobacterial cell wall, thereby disrupting its integrity and permeability. Ethambutol is primarily bacteriostatic against actively growing bacilli, preventing the development of drug resistance when used in combination. The combined mechanisms target multiple pathways, enhancing efficacy and reducing the likelihood of resistance emergence.
Commercial Brands (Alternatives)
No other brands found for this formula.