Indications and Usage
Isoniazid is recommended for all forms of tuberculos in which organisms are susceptible. However, active tuberculosis must be treated with multiple concomitant antituberculosis medications to prevent the emergence of drug resistance. Single-drug treatment of active tuberculos with isoniazid, or any other medication, is inadequate therapy.
Isoniazid is 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):
1. Persons with human immunodeficiency virus (HIV) infection ( 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. Candidates for
preventive therapy who have HIV infection should have a minimum of 12 months of therapy.
2. Close contacts of persons with newly diagnosed infectious tuberculosis ( 5 mm). In addition,
tuberculin-negative (< 5mm) children and adolescents who have been close contacts of in-
fectious persons within the past 3 months are candidates for preventive therapy until a repeat
tuberculin skin test is done 12 weeks after contact with the infectious source. If the repeat skin
test is positive (> 5 mm), therapy should be continued.
3. Recent converters, as indicated by a tuberculin skin test ( 10 mm increase within a 2-year
period for those < 35 years old;
15 mm increase for those
35 years of age). All infants and
children younger than 4 years of age with a > 10 mm skin test are included in this category.
4. Persons with abnormal chest radiographs that show fibrotic lesions likely to represent old
healed tuberculosis ( 5 mm). Candidates for preventive therapy who have fibrotic pulmonary
lesions consistent with healed tuberculosis or who have pulmonary silicosis should have 12
months of isoniazid or 4 months of isoniazid and rifampin, concomitantly.
5. Intravenous drug users known to be HIV-seronegative (> 10 mm).
6. Persons with the following medical conditions that have been reported to increase the risk of
tuberculosis ( 10 mm): silicosis; diabetes mellitus; prolonged therapy with adrenocorti-
costeroids; immunosuppressive therapy; some hematologic and reticuloendothelial diseases,
such as leukemia or Hodgkins disease; end-stage renal disease; clinical situations associated
with substantial rapid weight loss or chronic under nutrition (including: intestinal bypass
surgery for obesity, the postgastrectomy state (with or without weight loss), chronic peptic
ulcer disease, chronic malabsorption syndromes, and carcinomas of the oropharynx and upper
gastrointestinal tract that prevent adequate nutritional intake). Candidates for preventive
therapy who have fibrotic pulmonary lesions consistent with healed tuberculosis or who have
pulmonary silicosis should have 12 months of isoniazid or 4 months of isoniazid and
rifampin, concomitantly.
Additionally, in the absence of any of the above risk factors, persons under the age of 35 with a tuberculin skin test reaction of 10 mm or more are also appropriate candidates for preventive therapy if they are a member of any of the following high-incidence groups:
Foreign-born persons from high-prevalence countries who never received BCG vaccine.Medically under served low-income populations, including high-risk racial or ethnic minority populations, especially blacks, Hispanics, and Native Americans.Residents of facilities for long-term care (e.g., correctional institutions, nursing homes, and mental institutions).
Children who are less than 4 years old are candidates for isoniazid preventive therapy if they have > 10 mm induration from a PPD Mantoux tuberculin skin test.
Finally, persons under the age of 35 who a) have none of the above risk factors (1-6); b) belong to none of the high-incidence groups; and c) have a tuberculin skin test reaction of 15 mm or more, are appropriate candidates for preventive therapy.
The risk of hepatitis must be weighed against the risk of tuberculosis in positive tuberculin reactors over the age of 35. However, the use of isoniazid is recommended for those with the additional risk factors listed above (1-6) and on an individual basis insituations where there is likelihood of serious consequences to contacts who may become infected.