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The TOPCAT trial enrolled 3445 participants in 6 countries (1151 in the US, 326 in Canada, 167 in Brazil, 123 in Argentina, 1066 in Russia, and 612 in the Republic of Georgia). These were supposed to be patients who had heart failure with preserved ejection fraction (HFpEF), a group that makes up about half the population that have congestive heart failure.

The problems with the trial were apparent rather quickly. There was a significant regional variation in its results, and attempts to iron those out by looking into differences in diagnosis and patient classification didn't explain them. Spirononlactone showed statistically significant benefits (not huge, but real) in the North and South American patient cohort, but no difference at all in the Russia/Georgia group, and the event rate was much higher in the former as well.

[...] a significant number of patients in Russia and Georgia never ever got the drug. The Cardiobrief piece goes further, airing out the speculation that the spironolactone was, in fact, sold off on the open market by trial personnel rather than actually used as intended.

[...] It's hard enough to get solid numbers out of human clinical data as it is. Trial design and patient selection are issues that any clinical team wrestles with extensively before the first patient is even dosed. But if all this time, effort, care, and money is then wasted by people who don't even bother to give the drug to the study group, well. . .