Isoniazid

What it is and how it works

Mechanism of Action Isoniazid inhibits the synthesis of mycoloic acids, an essential component of the bacterial cell wall. At therapeutic levels isoniazid is bactericidal against actively growing intracellular and extracellular Mycobacterium tuberculosis organisms.

Indications

INDICATIONS AND USAGE Isoniazid tablets, USP are recommended for all forms of tuberculosis in which organisms are susceptible. However, active tuberculosis must be treated with multiple concomitant anti-tuberculosis medications to prevent the emergence of drug resistance. Single-drug treatment of active tuberculosis with isoniazid or any other medication, is inadequate therapy. Isoniazid tablets, USP are recommended as preventive therapy for the following groups, regardless of age. (Note: the criterion for a positive reaction to a skin test (in millimeters of induration) for each group is given in parenthesis): Persons with human immunodeficiency virus (HIV) infection (greater than or equal to 5 mm) and persons with risk factors for HIV infection whose HIV infection status is unknown but who are suspected of having HIV infection. Preventive therapy may be considered for HIV infected persons who are tuberculin-negative but belong to groups in which the prevalence of tuberculosis infection is high.

Dosage and administration (summary)

DOSAGE AND ADMINISTRATION (See also INDICATIONS AND USAGE ) NOTE For preventive therapy of tuberculous infection and treatment of tuberculosis, it is recommended that physicians be familiar with the following publications: the recommendations of the Advisory Council for the Elimination of Tuberculosis, published in the MMWR: vol 42; RR-4, 1993 and Treatment of Tuberculosis and Tuberculosis Infection in Adults and Children, American Journal of Respiratory and Critical Care Medicine: vol 149; 1359-1374, 1994. For Treatment of Tuberculosis Isoniazid is used in conjunction with other effective anti-tuberculous agents.

Contraindications

CONTRAINDICATIONS Isoniazid is contraindicated in patients who develop severe hypersensitivity reactions, including drug-induced hepatitis; previous isoniazid-associated hepatic injury; severe adverse reactions to isoniazid such as drug fever, chills, arthritis; and acute liver disease of any etiology.

Warnings and precautions

WARNINGS See the boxed warning . Severe Cutaneous Adverse Reactions Severe cutaneous adverse reactions (SCARs) including toxic epidermal necrolysis (TEN), Stevens-Johnson syndrome (SJS), drug reaction with eosinophilia and systemic symptoms (DRESS), and acute generalized exanthematous pustulosis (AGEP) have been reported with the use of isoniazid (see ADVERSE REACTIONS ). Symptoms can be serious and potentially life threatening. If symptoms or signs of SCARs develop, discontinue isoniazid tablets immediately and institute appropriate therapy.

Pregnancy

Pregnancy Teratogenic Effects Pregnancy Category C Isoniazid has been shown to have an embryocidal effect in rats and rabbits when given orally during pregnancy. Isoniazid was not teratogenic in reproduction studies in mice, rats and rabbits. There are no adequate and well-controlled studies in pregnant women.

Storage and supply

HOW SUPPLIED Isoniazid tablets, USP are available as follows: 100 mg: White to off-white, round, scored, flat-faced, beveled-edge tablet, debossed with 01 on one side and G over L on the other side. NDC 71335-3083-1: 30 Tablets in a BOTTLE Protect from moisture and light.

Source: Isoniazid (Isoniazid) — US FDA prescribing information, 2026-02-16, DailyMed. Summarised and shortened; the full label governs. Iranian registration, indications and labelling may differ.