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Generic Sildenafil Use and Mechanism of Action

Sildenafil definition and purpose

Sildenafil is a substance for oral use that is safe, effective and appropriate for the treatment of erectile dysfunction. Sildenafil can be used to treat impotence caused by organic, psychogenic, and mixed reasons.

Sildenafil mechanism of action

Sildenafil is inhibitory of PDE5, which makes it a vasoactive substance that improves the blood flow in the penis, since PDE5 is mostly found in the smooth muscle tissues in genitals. Sildenafil blocks the enzyme PDE5 that is responsible for signal transmission as an agent that makes the smooth muscles contract. When the enzyme is blocked by the use of sildenafil, the blood vessels of the smooth muscle tissues relax, expand and allow a powerful influx of blood that ultimately helps to form a hard erection.

Sildenafil does not affect sexual desire; it is the brain that transmits the signal of sexual arousal along the cGMP-specific pathways. In the absence of PDE5 enzyme that prevents the free flow of blood in the penis, it becomes possible to achieve erection. But sildenafil has no effect over the brain chemistry, therefore sexual desire should occur naturally.

Administration guide and doses

Sildenafil comes in doses 25mg, 50mg, and 100mg. The dose is established by a doctor based on patient’s response and tolerability.

Initial dosing: 25mg/50mg

Dose titration: 100mg (if no satisfactory results are achieved with the initial dose)

Note that your doctor will prescribe the minimal dose (sildenafil 25mg) in case you have compromised liver or kidney function or other comorbidity that calls for cautious use of sildenafil.

A tablet of sildenafil is taken 60 minutes before planned sexual activity with a glass of water; no chewing or crushing in the mouth is required.

Warnings and cautious use

  • Sildenafil should not be used in the presence of contraindications for sexual activity due to heart disease
  • Sildenafil dose should be minimal in patients with kidney or liver conditions, and in patients aged 75 and above
  • In case of developing painful erection or erection that lasts longer than 4 hours, difficulty breathing, severe allergic reactions, confusion, swelling of the mucuous tissues, pain in the chest or arm, report to ER without delay.

Side effects

The adverse reactions to sildenafil are fleeting and go away with continued use of the drug. Common side effects of sildenafil are:

  • Headache
  • Facial flushing
  • Sinusitis (stuffy nose)
  • Rhinitis (runny nose)
  • Stomach upset
  • Nausea
  • Dizziness
  • Ringing in the ears

Contraindications: who should not take sildenafil

Sildenafil contraindications are based on the vasoactive property of the drug. In this connection, it cannot be used by individuals with cardiovascular problems, and several other diseases affecting various systems of the body – see the table below.

Table 1. Conditions contradictory to the use of sildenafil

Body System Condition
Cardiovascular system Heart disease
Sickle cell disease
Hemorrhage disorder
Gastro-Intestinal System Stomach ulcer
Duodenum ulcer
Reproductive System Peyronie’s disease
Ocular System NAION
Angular glaucoma
Retinitis pigmentosa
Immune system Hypersensitivity to sildenafil
Hypersensitivity to lactose

Pharmacological incompatilities: sildenafil drug interactions

Do not take sildenafil with the following drugs:

Drug Group Examples
Alpha blockers Uroxatral (alfuzosin), Cardura (doxazosin), Minipress (prazosin), Flomax, in Jalyn (tamsulosin), terazosin
Antifungal drugs Onmel, Sporanox (itraconazole), Nizoral (ketoconazole)
Angina drugs Norvasc, Amturnide, Tekamlo (amlodipine)
Blood-thinning agents Coumadin, Jantoven (warfarin)
Some barbiturates Butapap, Fioricet, Fiorinal (butalbital), Seconal (secobarbital)
Beta-blockers Tenormin, Tenoretic (atenolol), Trandate (labetalol), Lopressor, Toprol XL, Dutoprol (metoprolol), Corgard, Corzide (nadolol), and Hemangeol, Inderal LA, InnoPran (propranolol)
HIV protease inhibitors Evotaz (atazanavir), Prezista (darunavir), Lexiva (fosamprenavir), Crixivan (indinavir), in Kaletra (lopinavir), Viracept (nelfinavir), Kaletra (ritonavir), Invirase (saquinavir), Aptivus (tipranavir)
Some antibiotics Rifampicin