Isoniazid as preventive therapy in HIV-infected intravenous drug abusers. A decision analysis.

Tuberculin skin testing is a notoriously poor marker of tuberculosis infection in patients who are serologically positive for the human immunodeficiency virus. A decision analysis was performed to determine if and when isoniazid should be prescribed to prevent tuberculosis in these patients. The decision was analyzed for an intravenous drug abuser who may have been anergic, while tuberculin test status, race, and gender were varied. The assumptions and parameter estimates selected for this investigation represent a highly conservative vantage point opposing the use of isoniazid as a preventive therapy. Nevertheless, results showed a benefit from the use of isoniazid as a preventive therapy for all groups, even without tuberculin testing, except tuberculin-negative black women. This benefit of isoniazid therapy increased patient life expectancy as much as 285 days. Further, the decisions continue to favor prescribing isoniazid even when the suspected incidence of tuberculosis infection falls as low as 3% to 8%. Tuberculin testing appears important primarily for black women, since those who have negative tuberculin skin tests may not be candidates for isoniazid therapy.