Ethambutol

Ethambutol is a synthetic, bacteriostatic antimycobacterial agent used primarily as part of a multi-drug protocol (a "cocktail") to treat stubborn mycobacterial infections (such as *M. tuberculosis*, *M. bovis*, *M. genavense*, and *M. avium-intracellulare* complex) in dogs, cats, and birds. **Clinical Pearl:** Monotherapy is strictly avoided due to the rapid development of step-wise resistance. It is typically combined with drugs like rifampin, isoniazid, enrofloxacin, or macrolides. > **Important Public Health Note:** Treating mycobacterial infections in veterinary medicine is highly controversial due to the significant zoonotic potential and public health risks, particularly for immunocompromised individuals in the household.

กลไกการออกฤทธิ์: Ethambutol is active only against actively dividing mycobacteria. Mechanistically, it inhibits the enzyme **arabinosyl transferase** → disrupts the synthesis of arabinogalactan → prevents the incorporation of **mycolic acid** into the mycobacterial cell wall. This disruption increases cell wall permeability, which allows other antimycobacterial drugs (like rifampin or isoniazid) to penetrate the cell more effectively. It also interferes with RNA synthesis. It has no appreciable activity against other non-mycobacterial bacteria or fungi.

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