Isoniazid(INH)
- Inhibits mycolic acid cellwall synthesis via oxygen dependent pathways.
- Bactericidal to both extracellular and intracellular organism
- SE:Peripheral neuritis,seizures,hepatitis,optic neuritis,hemolysis in G6PD deficiency,SLE like syndrome.
- Pyridoxine 10mg orally given as prophylaxis for optic neuritis.
- INH-Is Hepatotoxic and Neurotoxic.
Rifampicin
- Blocks RNA synthesis by blocking DNA dependent RNA polymerase.
- Bactericdal, acts best on intermittently dividing organisms(spurters)
- Hepatotoxic,enzyme inducer(P450)
- Orange colored urine and sweat.
Pyrazinamide
- Inhibits mycolic acid synthesis.
- Bactericidal to slowly dividing intracellular bacilli and those within caseous granuloma.
- More active at PH<6,god penetration into CNS.
- Hepatotoxic, hyperuricemia.
Ethambutol
- Inhibits arabinosyl transferases and interferes with mycolic acid incorporation into bacterial cell wall.
- Bacteriostatic, acts on fast dividing bacilli and atypical mycobacteria,least potent anti TB drug.
- Optic neuritis and Redgreen color vision disturbance.
- Ethambutol affect Eye.
Streptomycin
- Bind to 30S ribosomal subunit freeze initiation of protein synthesis and cause misreading of mRNA code.
- Bactericidal to extra cellular bacilli
- Ototoxic and nephrotoxic.
Importan Points: Most of these drugs are hepatotoxic except Streptomycin and Ethambutol.
INH resistance is associated with decreased catalase and peroxidase activity in the bacteria.
Leave a Reply