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★★★Well replicated — this finding’s sources average out to meta-analyses, systematic reviews or high-powered trials.
Quadrupling the dose added five metres to a six-minute walk
In pulmonary arterial hypertension, 20mg three times daily added 45 metres to a six-minute walk over placebo. At 40mg it added 46, and at 80mg it added 50.
What the study found
Four times the dose bought five extra metres of walking
In pulmonary arterial hypertension, a disease of raised pressure in the lung arteries, sildenafil at 20mg three times daily added 45 metres to a six-minute walk over placebo. At 40mg it added 46, at 80mg 50. That flatness is why the approved dose is the lowest one tested.
The caveat · A walking test, not survival
Six minutes of walking stands in for exercise capacity, not for living longer: the trial ran twelve weeks, was not powered for mortality, and found no significant difference in clinical worsening. It also enrolled only certain causes of raised lung pressure.