Chemo Drugs supplies Sildenafil Citrate Pharmaceutical Tablets. Chemo Drugs is an ISO 9001:2000 accredited company. The Sildenafil Citrate Pharmaceutical Tablets of trade names Viagra and Revatio is a drug used to treat erectile dysfunction and pulmonary arterial hypertension [PAH]. It acts by inhibiting cGMP specific phosphodiesterase type 5, an enzyme that regulates blood flow in the penis. Sildenafil Citrate Pharmaceutical Tablets is used for treatment for erectile dysfunction; its primary competitors on the market are tadalafil [Cialis] and vardenafil [Levitra].