USMLE

Ethambutol

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Antibiotics / Antiparasitics
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  30. Ethambutol
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Summary

Ethambutol is an antibiotic that inhibits the enzyme arabinosyltransferase, which is an enzyme that produces arabinogalactan, a building block of the mycobacterial cell wall seen in tuberculosis. It is used in combination with other antitubercular agents to treat tuberculosis. The main adverse effect of ethambutol is optic neuropathy, which can cause red-green color blindness, decreased visual acuity, or central scotoma. This side effect can be reversed by discontinuation of the drug.

Key Points

  • Ethambutol
    • Mechanism
      • Inhibits arabinosyltransferase
        • Prevents production of arabinogalactan, a key component of mycobacterial cell wall
    • Clinical Use
      • Mycobacterium tuberculosis
        • Part of RIPE regimen of rifamycin, isoniazid, pyrazinamide, and ethambutol
      • May be used to treat mycobacterium avium complex (MAC)
    • Adverse Effects
      • Optic neuropathy
        • Clinically manifests as red-green color blindness, decreased visual acuity, and central scotoma
        • Reversible with discontinuation of the drug