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Isoniazid: An overview

Richard H Drew, PharmD, MS, FCCP, FIDP
Section Editor
Stephen B Calderwood, MD
Deputy Editor
Elinor L Baron, MD, DTMH


Isoniazid is used for treatment of tuberculosis (as part of combination therapy) or for latent tuberculosis infection (as monotherapy or part of combination therapy). Less frequently, isoniazid may be used as part of a combination regimen for nontuberculous mycobacterial infections.

Basic issues related to clinical use of isoniazid will be reviewed here. The clinical settings in which isoniazid may be used are discussed separately. (See "Treatment of drug-susceptible pulmonary tuberculosis in HIV-uninfected adults" and "Treatment of latent tuberculosis infection in HIV-uninfected adults" and "Treatment of pulmonary tuberculosis in HIV-infected adults: Initiation of therapy" and "Treatment of latent tuberculosis infection in HIV-infected adults" and "Treatment of Mycobacterium avium complex lung infection in adults".)


Mechanism of action — The antimicrobial activity of isoniazid (INH) is selective for mycobacteria, likely due to its ability to inhibit mycolic acid synthesis, which interferes with cell wall synthesis, thereby producing a bactericidal effect [1]. INH also disrupts DNA, lipid, carbohydrate, and nicotinamide adenine dinucleotide (NAD) synthesis and/or metabolism.

Spectrum of activity — INH is active against intracellular and extracellular Mycobacterium tuberculosis. The organism is considered most susceptible to INH during its logarithmic phase of growth [1]. The minimum inhibitory concentration (MIC) of M. tuberculosis for INH ranges from 0.01 to 0.25 mcg/mL. The MICs and minimum bactericidal concentrations (MBCs) for the organism are equivalent for most isolates [1].

Of the atypical mycobacteria spp, M. kansasii and M. xenopi are considered the most susceptible, while M. avium complex is generally resistant to INH.

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Literature review current through: Dec 2017. | This topic last updated: Aug 25, 2017.
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