Antibacterial spectrum isoniazid

For bacilli in the stationary phase, isoniazid is bacteriostatic, but for rapidly dividing organisms, it is bactericidal. It is effective against intracellular bacteria. Isoniazid is specific for treatment of M. tuberculosis, although Mycobacterium kansasii(an organism that causes three percent of the clinical illness known as tuberculosis) may be susceptible at higher drug levels.