has part has role independent continuant antiviral agent sulfonamide antineoplastic agent vasodilator agent antihypertensive agent citrate salt sildenafil citrate CHEBI:58987 The citrate salt of sildenafil. neuroprotective agent ophthalmology drug EC 3.1.4.35 (3',5'-cyclic-GMP phosphodiesterase) inhibitor sildenafil