الفهرس 
A Pharmaceutical study on certain controlled release oral formulations of a phosphodiestrase-5 inhibitor
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Abstract
Sexual dysfunction refers to a problem during any phase of the sexual response cycle that prevents the man or couple from experiencing satisfaction from the activity. Types of sexual dysfunction include disorders involving sexual desire or libido, erection and ejaculation. Erectile dysfunction, also known as impotence, is a type of sexual dysfunction characterized by the inability to develop or maintain an erection of the penis during sexual activity. Erectile dysfunction is typically due to a combination of organic and psychololgical factors. Organic factors include cardiovascular diseases, diabetes, neurological problems, hormonal insufficiencies (hypogonadism) and drug side effects. Psychological factors include performance anxiety, stress and mental disorders. Vardenafil hydrochloride (VAR) is an erectile dysfunction treating drug. It acts through the inhibition of cGMP-specific PDE-5, the most active PDE involved in the termination of cGMP signaling in the penile corpus cavernosum and the erectile tissue in the penis. This, in turn, potentiates endogenous increases in cGMP levels in the corpus cavernosum and the vessels supplying it, thus increasing dilatation of the corporeal sinusoids allowing more blood flow, which induces an erection. VAR suffers from some limitations; including, (i) short elimination half -life (4-5 h), (ii) poor intestinal absorption due to the action of several drug efflux transporters like P-glycoprotein expressed in the luminal side of intestine, (iii) limited aqueous solubility (0.11 mg/mL), as well as (iv) the extensive first-pass metabolism (mediated by CYP3A isozymes) resulting in low absolute bioavailability (15%)