Patients aged 68 years were randomized after nsRP 1:1:1 to 9-month double-blind treatment ( DBT ) with tadalafil 5 mg once daily ( OaD ) , 20-mg tadalafil on-demand ( `` pro-re-nata '' ; PRN ) , or placebo , followed by 6-week drug-free washout and 3-month open-label OaD treatment .