Slide 143 Interventions for Tuberculosis Control and Elimination
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In The Union trial in patients with fibrotic lesions the efficacy of three, six, and 12 months isoniazid was evaluated. If all patients were analyzed, 12 months was not much superior to 6 months, and an analysis of these patients in the United States led them conclude that preventive therapy should be prescribed for six months.

The problem is differentiating between effectiveness and efficacy. Patients were given on-month supplies of drugs and it could not be ascertained whether they really took it. However, if only patients were considered who regularly came to obtain their one-month supplies throughout the assigned period of treatment ("completer-compliers"), the 12-month regimen was clearly superior to the six-month regimen. This led to some discordance in opinion in the United States, but initially the argument for the more "effective", but clearly less "efficacious" regimen won the day.

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Last update: September 29, 2010