It is somewhat less than five years since the first publications on isoniazid appeared in April, 1952,1-6 but this drug had then been under clinical investigation by two groups for more than half a year.5,6 It is possible, therefore, to look back on a full five years of clinical experience.
The marked symptomatic benefit noticed and resulting conspicuous exuberance displayed by many of the patients first to receive the isonicotinic acid hydrazides followed more often from iproniazid than from isoniazid.7 Because of its lower toxicity and its equal, or very nearly equal, objective benefit, isoniazid itself has virtually displaced the isopropyl derivative. Its less dramatic, and perhaps somewhat slower effect caused some disappointment when isoniazid became generally available. An even more disturbing factor, however, was the in vitro demonstration of relatively early increased bacterial resistance in successive cultures of sputum. It was then expected by many clinicians