Avanafil is a PDE5 inhibitor approved for erectile dysfunction by FDA and by EMA. Avanafil is known by the trademark names Stendra and Spedra and was developed by Vivus Inc. Avanafil selectively inhibits PDE5, thus inhibiting the degradation of cyclic guanosine monophosphate (cGMP) found in the smooth muscle of the corpus cavernosa of the penis. The physiologic mechanism of erection of the penis involves release of nitric oxide (NO) in the corpus cavernosum during sexual stimulation. NO then activates the enzyme guanylate cyclase, which results in increased levels of cGMP, producing smooth muscle relaxation in the corpus cavernosum and allowing inflow of blood. Avanafil has no direct relaxant effect on isolated human corpus cavernosum, but enhances the effect of NO by inhibiting PDE5, which is responsible for degradation of cGMP in the corpus cavernosum. Because sexual stimulation is required to initiate the local release of nitric oxide, the inhibition of PDE5 has noeffect in the absence of sexual stimulation. The advantage of avanafil is that it has very fast onset of action compared with other PDE5 inhibitors. It is absorbed quickly, reaching a maximum concentration in about 30–45 minutes. About two-thirds of the participants were able to engage in sexual activity within 15 minutes.

Vardenafil (Levitra) is an oral therapy for the treatment of erectile dysfunction. It is a selective inhibitor of cyclic guanosine monophosphate (cGMP)-specific phosphodiesterase type 5 (PDE5). Penile erection is a hemodynamic process initiated by the relaxation of smooth muscle in the corpus cavernosum and its associated arterioles. During sexual stimulation, nitric oxide is released from nerve endings and endothelial cells in the corpus cavernosum. Nitric oxide activates the enzyme guanylate cyclase resulting in increased synthesis of cyclic guanosine monophosphate (cGMP) in the smooth muscle cells of the corpus cavernosum. The cGMP in turn triggers smooth muscle relaxation, allowing increased blood flow into the penis, resulting in erection. The tissue concentration of cGMP is regulated by both the rates of synthesis and degradation via phosphodiesterases (PDEs). The most abundant PDE in the human corpus cavernosum is the cGMPspecific phosphodiesterase type 5 (PDE5); therefore, the inhibition of PDE5 enhances erectile function by increasing the amount of cGMP.

Tadalafil is used to treat male erectile dysfunction (impotence) and pulmonary arterial hypertension (PAH). Part of the physiological process of erection involves the release of nitric oxide (NO) in the corpus cavernosum. This then activates the enzyme guanylate cyclase which results in increased levels of cyclic guanosine monophosphate (cGMP), leading to smooth muscle relaxation in the corpus cavernosum, resulting in increased inflow of blood and an erection. Tadalafil is a potent and selective inhibitor of cGMP specific phosphodiesterase type 5 (PDE5) which is responsible for degradation of cGMP in the corpus cavernosum. This means that, with tadalafil on board, normal sexual stimulation leads to increased levels of cGMP in the corpus cavernosum which leads to better erections. Without sexual stimulation and no activation of the NO/cGMP system, tadalafil should not cause an erection.Tadalafil inhibits the cGMP specific phosphodiesterase type 5 (PDE5) which is responsible for degradation of cGMP in the corpus cavernosum located around the penis. Penile erection during sexual stimulation is caused by increased penile blood flow resulting from the relaxation of penile arteries and corpus cavernosal smooth muscle. This response is mediated by the release of nitric oxide (NO) from nerve terminals and endothelial cells, which stimulates the synthesis of cGMP in smooth muscle cells. Cyclic GMP causes smooth muscle relaxation and increased blood flow into the corpus cavernosum. The inhibition of phosphodiesterase type 5 (PDE5) by tadalafil enhances erectile function by increasing the amount of cGMP. Tadalafil is used for the treatment of erectile dysfunction.

Sildenafil (Viagra, Revatio) is a PDE5 inhibitor which was approved by FDA for the treatment of erectile disfunction and adults with pulmonary arterial hypertension. Upon administration sildenafil inhibits PDE5 and results in elevated level of cyclic guanosine monophosphate and smooth muscle relaxation.

Schering published xanthine PDE5 inhibitors with amino substituents in the imidazole 2-position, such as Dasantafil. Dasantafil, also known as SCH-446132, is a PDE5A inhibitor potentially for the treatment of erectile dysfunction. It had been in phase II clinical trials but there is no report for this compound recently.

SAR407899 is a potent, ATP-competitive Rho kinase inhibitor. It antihypertensive action in animals. Sanofi is developing SAR 407899 for the treatment of microvascular angina (Syndrome X). It was previously being developed in clinical trials for the treatment of diabetic neuropathies, diabetic nephropathies, erectile dysfunction, pulmonary hypertension, hypertension and kidney disorders, but development was discontinued for those indications.

Gisadenafil is a phosphodiesterase V inhibitor in clinical development at Pfizer. It had been in phase II clinical trials for the treatment of Benign prostatic hyperplasia; Chronic obstructive pulmonary disease; Erectile dysfunction; Overactive bladder. Treatment-emergent adverse events were: headache, myalgia, dyspepsia, back pain.

Acetildenafil is an analog of the phosphodiesterase inhibitor sildenafil, named for a substitution of an acetyl group for a sulfonyl group. This compound has been identified in herbal products marketed as aphrodisiacs. The physiological and toxicological properties of this analog have not been elucidated.

BAY 41-8543 (2-[1-[(2-fuorophenyl)methyl]-1H-pyrazolo[3,4-b]pyridin-3-yl]-5(4-morpholinyl)-4,6-pyrimidinediamine) is s potent nitric oxide (NO)-independent stimulator of soluble guanylate cyclase (sGC). BAY 41-8543 manifested both antiplatelet effect and vasodilatation. It has the potential of being a unique clinical utility for the treatment of cardiovascular diseases.

Estragole (ES) is a natural constituent of a number of plants (e.g. tarragon, sweet basil and sweet fennel) and their essential oils have been widely used in foodstuffs as flavouring agents. Estragole ES was given GRAS Generally Recognized As Safe status by the Flavor and Extract Manufacturer’s Association FEMA, 1965 and is approved by the Food and Drug Administration for food use 21 CFR code of Federal Regulation 121.1164 . Several studies with oral, i.p. or s.c. administration to CD-1 and B6C3F1 mice have shown the carcinogenicity of ES. In vivo and in vitro experimental assays have shown that EST has sedative, anticonvulsant, antioxidant, antimicrobial, and anesthetic activity.