- What is sildenafil, and how does it work (mechanism of action)?
- What brand names are available for sildenafil?
- Is sildenafil available as a generic drug?
- Do I need a prescription for sildenafil?
- What are the side effects of sildenafil?
- What is the dosage for sildenafil?
- Which drugs or supplements interact with sildenafil?
- Is sildenafil safe to take if I'm pregnant or breastfeeding?
- What else should I know about sildenafil?
What is sildenafil, and how does it work (mechanism of action)?
Viagra (sildenafil) is an oral drug that is used for treating impotence (or erectile disfunction, ED, the inability to attain or maintain a penile erection). It is in a class of drugs called phosphodiesterase inhibitors (PDE-5 inhibitors) that also includes
It has been estimated that impotence affects 140 million men worldwide. Over half of all men with impotence are thought to have some physical (medical) cause. The remainder are believed to have psychogenic causes of impotence. Medical causes of impotence include diabetes and circulatory, neurological, or urological conditions.
Penile erection is caused by the engorgement of the penis with blood. This engorgement occurs when the blood vessels delivering blood to the penis increase the delivery of blood and the blood vessels carrying blood away from the penis decrease the removal of blood. Under normal conditions, sexual stimulation leads to the production and release of nitric oxide in the penis. Nitric oxide then activates the enzyme, guanylate cyclase, which causes the production of cyclic guanosine monophosphate (cGMP). It is the cGMP that is primarily responsible for the erection by affecting the amount of blood that the blood vessels deliver and remove from the penis.
Viagra inhibits an enzyme called phosphodiesterase-5 (PDE5) which destroys the cGMP. Thus, Viagra prevents the destruction of cGMP and allows cGMP to accumulate and persist longer. The longer cGMP persists, the more prolonged the engorgement of the penis. The FDA approved Viagra in March 1998.
What are the side effects of sildenafil?
Approximately 15% of persons taking Viagra experience side effects. The most common side effects are:
Quick GuideErectile Dysfunction (ED) Causes and Treatment
What is the dosage for sildenafil?
- The usual recommended dose is 25 to 100 mg 1 hour before sexual activity.
- The maximum dose is 100 mg daily.
- The elderly (over 65 years of age) should start at 25 mg before sexual activity.
- Sildenafil is rapidly absorbed. Maximum observed plasma concentrations are reached within 30 to 120 minutes (median 60 minutes) of oral dosing in the fasted state. When sildenafil is taken with a high fat meal, the rate of absorption is reduced, with an average delay in the time to maximal concentration of 1 hour.
Which drugs or supplements interact with sildenafil?
Viagra increases the effects of the blood pressure lowering medications. It also increases the blood pressure lowering effects of nitrates, for example, isosorbide dinitrate (Isordil), isosorbide mononitrate (Imdur, Ismo, Monoket), nitroglycerin (Nitro-Dur, Transderm-Nitro) that are used primarily for treating angina. Patients taking nitrates should not receive Viagra.
Patients should not combine Viagra with other PDE5 inhibitors (for example, vardenafil [Levitra], tadalafil [Cialis]).
Cimetidine (Tagamet), erythromycin, ketoconazole (Nizoral), itraconazole (Sporanox), atazanavir (Reyataz), and mibefradil (Posicor) can cause marked increases in the amount of Viagra in the body. Patients taking these medications should be observed carefully if sildenafil is used.
It is expected that rifampin will decrease blood levels of Viagra and probably reduce its effectiveness.
Is sildenafil safe to take if I'm pregnant or breastfeeding?
Although extensive testing in animals has demonstrated no negative effects on the fetus, Viagra has not been studied in pregnant women. There is no effect on sperm count or motility of sperm in men.
It is not known whether sildenafil is excreted into breast milk.
What else should I know about sildenafil?
What preparations of sildenafil are available?
Sildenafil (Viagra) is a blue, film-coated, rounded, diamond-shaped tablet that comes in 25, 50, and 100 mg tablets for treating impotence.
How should I keep sildenafil stored?
Tablets should be kept at room temperature between 15 C and 30 C (59 F and 86 F).
Reference: FDA Prescribing Information.
Sildenafil (Viagra) is a medication prescribed for the treatment of impotence (erectile dysfunction, ED) caused by medical or psychological conditions. Side effects, drug interactions, warnings and precautions, and patient safety information should be reviewed prior to taking any medication.
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Top sildenafil Related ArticlesComplete List
Erectile Dysfunction (ED, Impotence)Erectile dysfunction (ED, impotence) is the failure to achieve or maintain an erection. There are many potential underlying causes of erectile dysfunction, including stress and emotional problems, brain dysfunction, problems with blood supply to the penis, and structural problems with the penis. Erectile dysfunction is diagnosed by taking the patient's history and physical exam. Blood tests measuring kidney function and blood sugar, cholesterol, hormone, and prostate-specific antigen (PSA) levels may be ordered. Urinalysis, ultrasound, and other more sophisticated tests may be required. The treatment of erectile dysfunction depends on the underlying cause. Medications, penile injections, penile implants, and vacuum devices may be used. Treatment for erectile dysfunction is usually successful. The patient should manage heart disease risk factors (high blood pressure, high cholesterol, diabetes) as they are related to erectile dysfunction risk.
Take the Impotence QuizDid you know that certain medical condition may be responsible for ED? Some causes of impotence are medically treatable and reversible. Learn more about what can be done about erectile dysfunction with the Impotence Quiz.
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MS (Multiple Sclerosis) Symptoms and Treatments
Multiple sclerosis (MS) symptoms vary from person to person, and can last for days to months without periods of remission. Symptoms of MS include problems with the:
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Treatment options vary depending on the type and severity of symptoms. Medications may be prescribed to manage MS symptoms.
Night sweats are severe hot flashes that occur at night and result in a drenching sweat. The causes of night sweats in most people are not serious, like menopause in women, sleep apnea, medications, alcohol withdrawal, and thyroid problems. However, more serious diseases like cancer and HIV also can cause night sweats. Your doctor will treat your night sweats depending upon the cause.
You may experience other signs and symptoms that are associated with night sweats, which depend upon the cause, but may include:
- Fever, shaking, and chills with a fever caused by an infection like the flu or pneumonia.
- Unexplained weight loss due to lymphoma.
- Women in perimenopause or menopause may also have vaginal dryness, mood swings, and hot flashes during the day.
- Low blood sugar in people with diabetes.
Other causes of night sweats include:
- Medications like NSAIDs (aspirin, acetaminophen, ibuprofen (Motrin, Advil), and naproxen (Aleve, Naprosyn), antidepressants, sildenafil (Viagra), and abuse of prescription or illegal drugs and drug withdrawal.
- Hormone disorders like pheochromocytoma and carcinoid syndrome
- Idiopathic hyperhidrosis
- Infections like endocarditis, AIDs, and abscesses.
- Alcoholism and alcohol withdrawal
- Drug abuse, addiction, and withdrawal
A doctor or other health care professional can treat your night sweats after the cause has been diagnosed.
Penis PictureThe penis is the male sex organ, reaching its full size during puberty. See a picture of the Penis and learn more about the health topic.
Peyronie's Disease (Curvature of the Penis)Peyronie's disease or curvature of the penis (Peyronie disease) is a condition in which scar tissue develops inside the penis. This scar tissue causes the penis to develop an abnormal curvature in the scarred area. At this time, there is no known cause of Peyronie's disease. Symptoms of Peyronie's disease include:
- pain during intercourse or ejaculation,
- the inability to have sexual intercourse,
- an indentation of the shaft at the site where there is plaque or scarring, and
- an angulation of the penis when erect or flaccid.
Pulmonary hypertension is an increase pressure in the pulmonary arteries that carry blood from the lungs to the heart. The most common symptoms are fatigue and difficulty breathing. If the condition goes undiagnosed, more severe symptoms may occur, for example:
- Ankle swelling (edema)
- Heart palpitations
- Chest pain
- Decreased appetite
- Pain in the upper right side of the belly (abdomen)
- Fainting (syncope)
- Lightheadedness, particularly during physical activity
- Swelling in the legs and ankles
- A bluish color to the lips and skin
People at risk of developing pulmonary hypertension are those who:
- Live at high altitudes
- Have a family history of the condition.
- Have diseases and conditions that may put them at risk of developing pulmonary hypertension
- Use illegal drugs like cocaine, and certain diet drugs.
NIH. National Heart, Lung, and Blood Institute. "What is Pulmonary Hypertension?" Updated: Aug 2011
NIH. PubMed Health. "Pulmonary Hypertension (PH)."
CDC. Division for Heart Disease and Stroke Prevention. "Pulmonary Hypertension Fact Sheet." Updated: Jul 22, 2014.
SclerodermaScleroderma is an autoimmune disease of the connective tissue. It is characterized by the formation of scar tissue (fibrosis) in the skin and organs of the body, leading to thickness and firmness of involved areas. Scleroderma is also referred to as systemic sclerosis, and the cause is unknown. Treatment of scleroderma is directed toward the individual features that are most troubling to the patient.
Sex & Love QuizRelationships, sex, and love! Could it be that what motivates physical attraction in us may be all in our minds? Take the Sex & Love Quiz to challenge yourself on healthy human sexuality!
Sex-Drive KillersNoticing a lack of intimacy with your partner? Here we explore how stress, lack of sleep, weight gain, depression and low T can cause low sex drive in men and women.
Sexual (Sex) Problems in MenMale sexual dysfunction can be caused by physical or psychological problems. Common sexual problems in men include erectile dysfunction (impotence or ED), premature ejaculation, and loss of libido. Treatment for sexual dysfunction in men may involve medication, hormone therapy, psychological therapy, and the use of mechanical aids.
Sexual (Sex) Problems in WomenSexual dysfunction refers to a problem that arises during any phase of the sexual response cycle, preventing an individual or couple from experiencing sexual satisfaction. Physical, medical, and psychological conditions may affect sexual functioning, resulting in inhibited sexual desire, inability to become aroused, lack of orgasm, and painful intercourse. Treating the underlying physical and psychological problems usually resolves most female sexual problems.
Sexual and Urologic Problems of DiabetesHaving diabetes can mean early onset and increased severity of bladder symptoms (urinary incontinence and urinary tract infections) and changes in sexual function. Men may have erectile dysfunction; and women may have problems with sexual response and vaginal lubrication. Keep your diabetes under control, and you can lower your risk of sexual and urologic problems.