Synonyms: 5-[2-Ethoxy-5-[(4-methyl-4-oxidopiperazin-1-yl)sulfonyl]phenyl]-1-methyl-3-propyl-6,7-dihydro-1Hpyrazolo[4,3-d]pyrimidin-7-one, Sildenafil N-Oxide,7H-Pyrazolo[4,3-d]pyrimidin-7-one, 5-[2-ethoxy-5-[(4-methyl-4-oxido-1-piperazinyl)sulfonyl]phenyl]-1,6-dihydro-1-methyl-3-propyl-, 5-[2-Ethoxy-5-[(4-methyl-4-oxido-1-piperazinyl)sulfonyl]phenyl]-1,6-dihydro-1-methyl-3-propyl-7H-pyrazolo[4,3-d]pyrimidin-7-one, Sildenafil-N-oxide