Ethambutol is a bacteriostatic antimycobacterial agent, classified as a first-line drug for the treatment of all forms of tuberculosis (TB). It is a critical component of Directly Observed Treatment, Short-course (DOTS) and other regimens recommended by the Revised National Tuberculosis Control Programme (RNTCP), now known as the National Tuberculosis Elimination Programme (NTEP) in India. Its primary role is to prevent the emergence of resistance to other drugs, particularly rifampicin. The 800mg strength is a standard adult dose used in the continuation phase of treatment.
Adult: 15-25 mg/kg body weight once daily. Standard adult dose for weight ≥55kg is 800mg (approx. 15mg/kg). For intensive phase (under 55kg), 600mg is used. Maximum daily dose should not exceed 25 mg/kg.
Note: Administer once daily, preferably at the same time each day. Can be taken with or without food. If GI upset occurs, take with food. Tablet should be swallowed whole with a full glass of water. Do not crush or chew.
Ethambutol inhibits arabinosyl transferase enzymes (specifically EmbA, EmbB, and EmbC) that are encoded by the *embCAB* operon. These enzymes are crucial for the polymerization of cell wall arabinogalactan, a major structural component of the mycobacterial cell wall. By inhibiting this process, ethambutol disrupts the formation of the mycobacterial cell wall, leading to impaired cell wall integrity and bacteriostatic activity.
Pregnancy: Pregnancy Category C (US FDA). Animal studies have shown fetal abnormalities. Use during pregnancy only if the potential benefit justifies the potential risk to the fetus. It is considered part of first-line TB treatment in pregnant women by WHO and NTEP India when indicated, as untreated TB poses greater risk.
Driving: Patients should be cautioned that dizziness, blurred vision, or visual disturbances may impair the ability to drive or operate machinery. They should not drive if they experience any visual symptoms.
| Aluminum hydroxide (Antacids) | May decrease absorption of ethambutol. Separate administration by at least 4 hours. | Moderate |
| Other Neurotoxic drugs (e.g., Chloroquine, Isoniazid, Disulfiram) | Additive risk of peripheral neuropathy and optic neuritis. | Major |
| Aminoglycosides (e.g., Streptomycin, Amikacin) | Additive ototoxicity and nephrotoxicity. | Moderate |
| Allopurinol/Colchicine/Probenecid | May be used to manage ethambutol-induced hyperuricemia/gout. No direct harmful interaction. | Minor |
Same composition (Ethambutol (800mg)), different brands: