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Sildenafil, the prototypical PDE5 inhibitor
Sildenafil, the prototypical PDE5 inhibitor

A phosphodiesterase type 5 inhibitor, often shortened to PDE5 inhibitor, is a drug used to block the degradative action of phosphodiesterase type 5 on cyclic GMP in the smooth muscle cells lining the blood vessels supplying the corpus cavernosum of the penis. Sildenafil citrate, sold as Viagra, Revatio and under various other trade names is a drug used to treat Erectile dysfunction (male impotence Medication, also referred to as medicine, can be loosely defined as any substance intended for use in the diagnosis cure mitigation treatment or prevention of disease A phosphodiesterase is any Enzyme that breaks a Phosphodiester bond. Cyclic guanosine monophosphate ( cGMP) is a Cyclic nucleotide derived from Guanosine triphosphate (GTP Smooth muscle is a type of non- Striated muscle, found within the Tunica media layer of large and small Arteries and Veins, the bladder The penis (plural penises, penes These drugs are used in the treatment of erectile dysfunction, and were the first effective oral treatment available for the condition. Because PDE5 is also present in the arterial wall smooth muscle within the lungs, PDE5 inhibitors have also been explored for the treatment of pulmonary hypertension, a disease in which blood vessels in the lungs become abnormally narrow. Smooth muscle is a type of non- Striated muscle, found within the Tunica media layer of large and small Arteries and Veins, the bladder lung is the essential Respiration organ in air-breathing Animals including most Tetrapods a few Fish and a few Snails The most primitive In Medicine, pulmonary hypertension (PH is an increase in blood pressure in the Pulmonary artery, Pulmonary vein, or pulmonary capillaries together known

Contents

Indications

PDE5 inhibitors are clinically indicated for the treatment of erectile dysfunction. Sildenafil, one of the PDE5 inhibitors, is also indicated for the treatment of pulmonary hypertension, and the chemically related drugs tadalafil and vardenafil have been studied as other possible treatments for this disease. Sildenafil citrate, sold as Viagra, Revatio and under various other trade names is a drug used to treat Erectile dysfunction (male impotence In Medicine, pulmonary hypertension (PH is an increase in blood pressure in the Pulmonary artery, Pulmonary vein, or pulmonary capillaries together known Tadalafil is an orally administered drug for treating impotence ( Erectile dysfunction) that initially was developed by the Biotechnology company ICOS Vardenafil ( INN) is a PDE5 inhibitor used for treating impotence ( Erectile dysfunction) that is sold under the trade name Levitra ( Bayer

Sildenafil, the prototypical PDE5 inhibitor, was originally discovered during the search of a novel treatment for angina. Angina pectoris, commonly known as angina, is severe Chest pain due to Ischemia (a lack of blood and hence Oxygen supply of the heart Recent studies are exploring its potential for increasing neurogenesis after stroke. Neurogenesis ( birth of Neurons ' is the process by which neurons are created A stroke is the rapidly developing loss of brain functions due to a disturbance in the blood vessels supplying blood to the brain [1]

Contraindications

PDE5 inhibitors are contraindicated in those taking nitrate medication. In Inorganic chemistry, a nitrate is a salt of Nitric acid with an Ion composed of one Nitrogen and three Oxygen atoms They are also contraindicated in men for whom sexual intercourse is inadvisable due to cardiovascular risk factors. [2]

Adverse reactions

The occurrence of adverse drug reactions (ADRs) with PDE5 inhibitors appears to be dose related. An adverse drug reaction (abbreviated ADR) or adverse drug event (abbreviated ADE) is an expression that describes the unwanted negative consequences Headache is a very common ADR, occurring in >10% of patients. A headache ( cephalalgia in medical terminology is a condition of pain in the Head; sometimes Neck or upper back pain may also be interpreted Other common ADRs include: dizziness, flushing, dyspepsia, nasal congestion or rhinitis. Dyspepsia (from the Greek "δυς-" (Dys- and "πέψη" (Pepse known in plain English as indigestion, meaning hard [2]

On October 18, 2007, the FDA announced that a warning about possible sudden hearing loss would be added to drug labels of PDE5 inhibitors. Events 1009 - The Church of the Holy Sepulchre, a Christian church in Jerusalem, is completely destroyed by the Fatimid Year 2007 ( MMVII) was a Common year starting on Monday of the Gregorian calendar in the 21st century. [3]

Other ADRs and their incidence vary with the agent and are listed in their individual pages.

Drug interactions

PDE5 inhibitors are primarily metabolised by the cytochrome P450 enzyme CYP3A4. Cytochrome P450 (abbreviated CYP, P450, infrequently CYP450) is a very large and diverse superfamily of Hemoproteins found in all Domains Cytochrome P450 3A4 (abbreviated CYP3A4) ( a member of the Cytochrome P450 mixed-function oxidase system is one of the most important enzymes involved in the metabolism The potential exists for adverse drug interactions with other drugs which inhibit or induce CYP3A4, including HIV protease inhibitors, ketoconazole, itraconazole, and other anti-hypertensive drugs such as Nitro-spray (due to its capacity to diminish blood pressure). For natural protease inhibitors please see Protease inhibitor (biology Protease inhibitors (PIs are a class of Medications used Ketoconazole is a synthetic Antifungal drug used to prevent and treat skin and fungal infections especially in immunocompromised patients such as those Itraconazole (marketed as Sporanox by Janssen Pharmaceutica) invented in 1984 is a Triazole Antifungal agent that is prescribed to patients [2]

Examples

Sildenafil was the prototypical member of the PDE5 inhibitors. Two other agents, with their own advantages/disadvantages, are also available, and several other are in development.

Mode of action

Part of the physiological process of erection involves the release of nitric oxide (NO) in vasculature of the corpus cavernosum as a result of sexual stimulation. Sildenafil citrate, sold as Viagra, Revatio and under various other trade names is a drug used to treat Erectile dysfunction (male impotence Tadalafil is an orally administered drug for treating impotence ( Erectile dysfunction) that initially was developed by the Biotechnology company ICOS Vardenafil ( INN) is a PDE5 inhibitor used for treating impotence ( Erectile dysfunction) that is sold under the trade name Levitra ( Bayer Nitric oxide or nitrogen monoxide is a Chemical compound with Chemical formula N[[Oxygen O]] NO activates the enzyme guanylate cyclase which results in increased levels of cyclic guanosine monophosphate (cGMP), leading to smooth muscle relaxation in blood vessels supplying the corpus cavernosum, resulting in increased blood flow and an erection. Guanylate cyclase ( also known as guanylyl cyclase or GC) is a Lyase Enzyme. Cyclic guanosine monophosphate ( cGMP) is a Cyclic nucleotide derived from Guanosine triphosphate (GTP Smooth muscle is a type of non- Striated muscle, found within the Tunica media layer of large and small Arteries and Veins, the bladder

PDE5 inhibitors inhibit the degradation of cGMP by phosphodiesterase type 5 (PDE5), increasing bloodflow to the penis during sexual stimulation. A phosphodiesterase is any Enzyme that breaks a Phosphodiester bond.

This mode of action means that PDE5 inhibitors are ineffective without sexual stimulation.

Notes

  1. ^ Zhang, R. et al. Sildenafil (Viagra) induces neurogenesis and promotes functional recovery after stroke in rats. Stroke 33, 2675–80 (2002)
  2. ^ a b c Rossi S, editor. Australian Medicines Handbook 2006. The Australian Medicines Handbook or AMH is a medical reference text commonly used in practice by health professionals (particularly General practitioners Adelaide: Australian Medicines Handbook; 2006.
  3. ^ FDA Announces Revisions to Labels for Cialis, Levitra and Viagra. Food and Drug Administration (2007-10-18). Year 2007 ( MMVII) was a Common year starting on Monday of the Gregorian calendar in the 21st century. Events 1009 - The Church of the Holy Sepulchre, a Christian church in Jerusalem, is completely destroyed by the Fatimid Retrieved on 2007-12-08. Year 2007 ( MMVII) was a Common year starting on Monday of the Gregorian calendar in the 21st century. Events 1609 - Biblioteca Ambrosiana opens its reading room the second public library of Europe.

References

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