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Isoniazid
- Uses: clinically manifest disease; prophylaxis
- Mechanism: inhibits synthesis of mycolic acids
- Pharmacokinetics: readily absorbed in GI tract; effective intracellularly and extracellularly; good CNS penetration; inactivated by acetylation (population variability)
- Adverse effects: peripheral and central neurotoxicity (prevented by coadministration of B6); hepatotoxicity
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Rifampin
- Uses: First line in combo; can be used as prophylaxis against other infections
- Mechanism: inhibits bacterial DNA dependent RNA polymerase
- Pharmacokinetics: well absorbed from GI tract; excreted into bodily fluids, turning them orange-red
- Adverse effects: usually well tolerated but can cause jaundice, rash, thrombocytopenia, nephritis, & hepatotoxicity
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Ethambutol
- Uses: First line in combo
- Mechanism: inhibits synthesis of arabinogalactan
- Pharmacokinetics: readily absorbed from GI tract; excreted in urine; does not cross blood-brain barrier
- Advere effects: few side effects; optic neuritis; try to avoid in children
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Pyrazinamide
- Uses: short term therapy in combo
- Mechanism: inhibits mycobacterial fatty acid synthase I gene (involved in mycolic acid synthesis)
- Pharmacokinetics: readily absorbed in GI tract and mostly excreted in the urine
- Adverse effects: hepatotoxicity; contraindicated in patients with severe liver disease or gout
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