Synonyms: Piperazine,1-[[3-(4,7-dihydro-1-methyl-7-oxo-3-propyl-1H-pyrazolo[4,3-d]pyrimidin-5-yl)-4-ethoxyphenyl]sulfonyl]-(9CI); 1H-Pyrazolo[4,3-d]pyrimidine, piperazine deriv.;5-[2-Ethoxy-5-(piperazin-1-ylsulfonyl)phenyl]-1-methyl-3-propyl-1,6-dihydro-7H-pyrazolo[4,3-d]pyrimidin-7-one;Desmethylsildenafil; N-Demethylsildenafil; N-Desmethylsildenafil; UK 103320