Sunday, August 12, 2007

Side Effects of Viagra®

Very few drugs work perfectly, and Viagra® is no exception. Just about every drug has side effects that arise because the drug is flowing throughout the body and may affect parts of the body unintentionally. For example, aspirin is a drug that relieves pain, but this same drug can also erode the stomach lining and thin the blood. Those are side effects of aspirin.

Viagra® has several side effects of which patients need to be aware.

The first problem comes because Viagra® happens to have a spillover effect. It blocks PDE5, but it also has an effect on PDE6. It turns out that PDE6 is used in the cone cells in the retina, so Viagra® can have an effect on color vision. Many people who take Viagra® notice a change in the way they perceive green and blue colors, or they see the world with a bluish tinge for several hours. For this reason, pilots cannot take Viagra® within 12 hours of a flight.

The second problem comes for people who are taking drugs like nitroglycerin for angina. Nitroglycerin works by increasing nitric oxide, and it helps with angina by opening up the arteries that supply the heart with oxygen. If you take nitroglycerin and Viagra® together, the increased nitric oxide plus the blocking of PDE5 can lead to problems.

Other problems with Viagra® can include little things like headaches (the drug, as a side effect in some men, opens up arteries in the brain's lining and causes excess pressure) and big things like heart attacks. The possibility of heart attacks is one reason why Viagra® is a prescription drug rather than an over-the-counter drug like aspirin. A doctor needs to understand your medical history and make sure that Viagra® won't cause a heart attack. Occasional patients who take Viagra® get painful, long-lasting erections and have to see a doctor to solve the problem.

Finally, there is some concern that some men, especially younger men who take Viagra® recreationally and who don't really need it for physical reasons, may end up with a dependency on the drug. That is, they may become unable to maintain an erection without taking Viagra®.

For more information about side effects, see RxList: Viagra® Side Effects.

What about Cialis® and Levitra®?
Viagra® is a hugely successful drug, and other drug companies wanted a piece of the action. They developed different chemicals to block the PDE5 enzyme and created two new drugs: Cialis® (tadalafil) and Levitra® (vardenafil).

Because Cialis® and Levitra® block the PDE5 enzyme, they work exactly the same way as Viagra®. They help men who have trouble maintaining an erection because of blood flow problems, and they only work when the man is sexually aroused.

Because they block PDE5 with different chemicals, however, there are some important differences between the three drugs. For example:

* Only Viagra® causes color-vision problems.
* Cialis® causes muscle aches in about 5 percent of patients.
* Viagra® and Levitra® last about four hours in the bloodstream. Cialis® stays in the bloodstream much longer (it has a 17.5-hour half life) and can therefore be effective for more than a day.

Impotence

Impotence is the inability to achieve and maintain an erection, which is necessary for the penis to penetrate the vagina during sexual intercourse. The corpora cavernosa of the penis normally fill with blood during sexual excitement, which causes the penis to become rigid and erect. Impotence is a partial or total impairment of this function.

Types

There are two types of impotence: primary impotence, in which a man is never able to have an erection adequate for sexual intercourse; and secondary impotence, in which a man quite often fails to complete intercourse to the satisfaction of both partners. Secondary impotence is the more common type.

Many men experience temporary impotence at some point in their lives, but chronic (recurring) impotence can lower a man's self-esteem and put a strain on his marriage or social relationships.

Causes

Impotence can be caused by either physical or psychological problems. Impotence may be brought on by stress related to a job, fear of causing pregnancy, unresolved conflicts about sexuality, or fear of sex after a heart attack or major surgery. Drug and alcohol abuse are also among the leading causes of impotence.

Physical factors known to trigger impotence include the following: an imbalance in the hormonal system that causes a decrease in production of testosterone (the male hormone necessary for an erection); the use of certain drugs, particularly diuretics and beta-blockers for the treatment of high blood pressure; diseases of the nervous system, such as multiple sclerosis; structural abnormalities of the penis; injury to the penis; and malfunctioning of the circulatory system, which can interfere with the blood flow to the penis. Vascular problems (including those from diabetes) may also be associated with symptoms.

Symptoms

The major symptom of impotence is inability to attain or maintain erection of the penis for sexual intercourse. This may be accompanied by a lack of interest in sex, but it does not necessarily mean infertility (the inability to father a child).

Diagnosis

Several tests can help to diagnose the cause of impotence. A blood test will show whether adequate levels of testosterone are present. With a blood pressure cuff specially designed to wrap around the penis and an ultrasound study (a technique that uses sound waves to create images of internal structures), blood vessel problems in the penis can often be detected. Another test registers the size of erections that naturally occur during sleep; if erections do not occur during sleep, a physical cause, rather than an emotional one, is likely.

Treatment

To determine if certain medications might be the cause of impotence, prescription drugs may be replaced or eliminated one at a time. If impotence has a physical basis, a number of treatments are available. The drugs sildenafil (Viagra) and varenafil (Levitra) are often used for impotence treatment. Injections of testosterone and other hormones may relieve some problems. Surgery may be necessary to repair the arteries and veins that carry blood to and from the penis.

The use of penile implants is a successful new treatment for impotence, with several varieties now in use. One is a silicone rod that is implanted in the corpora cavernosa, resulting in a permanent partial erection. Another is a flexible silver wire surrounded by silicone, which allows manipulation of the penis to an erect position for intercourse. A third model consists of balloonlike cylinders implanted in the corpora cavernosa and connected to a container of fluid; with the use of a hand pump, the cylinders may be filled with the fluid, in much the same way that blood normally fills the penis during an erection.

Counseling by a psychologist or trained sex therapist may be recommended for men whose impotence seems to stem from emotional problems. Counseling may also help those with physical disorders learn to deal with their impotence.

Prevention

Avoiding drug and alcohol abuse, as well as eliminating or coping with stress, should help prevent at least some episodes of secondary impotence.

Saturday, August 11, 2007

BRAND NAME: Levitra

GENERIC NAME: vardenafil
BRAND NAME: Levitra

DRUG CLASS AND MECHANISM: Vardenafil is an oral drug that is used to treat impotence (the inability to attain or maintain a penile erection.). It is a phosphodiesterase inhibitor that is similar to sildenafil (Viagra).

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 in size and increase the delivery of blood to the penis. At the same time, the blood vessels carrying blood away from the penis decrease in size and decrease the removal of blood from the penis. Sexual stimulation that leads to the engorgement and erection causes the production and release of nitric oxide in the penis. Nitric oxide then activates the enzyme, guanylate cyclase to produce cyclic guanosine monophosphate (cGMP). The cGMP is primarily responsible for increasing and decreasing the size of the blood vessels carrying blood to and from the penis, respectively. Vardenafil prevents an enzyme called phosphodiesterase-5 from destroying cGMP so that cGMP persists longer. The longer cGMP persists, the more prolonged the engorgement of the penis. Vardenafil was approved by the FDA in August, 2003.

PRESCRIPTION: Yes

GENERIC AVAILABLE: No

PREPARATIONS: Tablets: 2.5, 5, 10 and 20 mg

STORAGE: Vardenafil should be stored at room temperature between 15-30°C (59-86°F).

PRESCRIBED FOR: Vardenafil is used for the treatment of impotence.

DOSING: For most individuals, the recommended dose of vardenafil is 10 mg per day taken 60 minutes before intercourse. If there is no response or side effects, the dose may be increased to 20 mg or, if there are side effects, it may be reduced to 5 mg. Individuals 65 years of age or older should begin therapy with 5 mg. Individuals who are taking medications that increase the blood levels of vardenafil should start treatment with 2.5 to 5 mg of vardenafil. (See drug interactions.)

DRUG INTERACTIONS: The breakdown and elimination of vardenafil from the body is inhibited by erythromycin, ketoconazole (Nizoral), itraconazole (Sporanox), indinavir (Crixivan) and ritonavir (Norvir). Therefore, these drugs increase the concentration of vardenafil in the blood. If these drugs are being used at the same time as vardenafil, the dose of vardenafil should be reduced in order to avoid side effects from vardenafil.

Vardenafil reduces the concentration of ritonavir and indinavir and may reduce the effect these drugs.

Vardenafil increases the heart rate and also exaggerates the blood pressure lowering effects of nitrates (e.g. nitroglycerine). In patients who take nitrates for chest pain (angina), vardenafil could cause chest pain by increasing heart rate and lowering blood pressure. Therefore, patients with angina should not use vardenafil. Vardenafil also exaggerates the blood pressure lowering effects of alpha-blocking drugs, e.g. terazosin (Hytrin), and should not be used by individuals who also use alpha-blockers.

PREGNANCY: Vardenafil is not approved for use in women.

NURSING MOTHERS: Vardenafil has not been evaluated in women who are breastfeeding.

SIDE EFFECTS: The most common side effects of vardenafil are facial flushing (reddening), headaches, stomach upset, diarrhea, flu like symptoms and nausea. Vardenafil also may cause chest pain, low blood pressure, blurred vision and changes in color vision, abnormal ejaculation and priapism (painful erection).

BRAND NAME: Viagra, Revatio

GENERIC NAME: sildenafil
BRAND NAME: Viagra, Revatio

DRUG CLASS AND MECHANISM: 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.

Sildenafil also reduces the pressure in the pulmonary artery in a serious condition called pulmonary arterial hypertension.

Sildenafil inhibits an enzyme called phosphodiesterase-5 (PDE5) which destroys the cGMP. Thus, sildenafil 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.

PRESCRIPTION: Yes

GENERIC AVAILABLE: No

PREPARATIONS: Viagra is a blue, film-coated, rounded, diamond-shaped tablets that comes in 25, 50, and 100 mg tablets for treating impotence. Revatio comes in a 20 mg tablet and is used for treating pulmonary arterial hypertension..

STORAGE: Tablets should be kept at room temperature, 15- 30°C (59-86°F).

PRESCRIBED FOR: Sildenafil is used for the treatment of erectile dysfunction of either organic (medical condition) or psychogenic (psychological) cause and for pulmonary arterial hypertension.

DOSING: 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.

DRUG INTERACTIONS: Sildenafil increases the effects of the blood pressure lowering medications. It also increases the blood pressure lowering effects of nitrates, e.g. 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 sildenafil.

Cimetidine (Tagamet), erythromycin, ketoconazole (Nizoral), itraconazole (Sporanox) and mibefradil (Posicor) can cause marked increases in the amount of sildenafil 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 sildenafil and probably reduce its effectiveness.

PREGNANCY: Although extensive testing in animals has demonstrated no negative effects on the fetus, sildenafil has not been studied in pregnant women. There is no effect on sperm count or motility of sperm in men.

NURSING MOTHERS: It is not known whether sildenafil is excreted into breast milk.

SIDE EFFECTS: Approximately 15% of persons taking sildenafil experience side effects. The most common side effects are facial flushing (1 in 10), headaches (1 in 6), stomach pain, nasal congestion, nausea, diarrhea, and an inability to differentiate between the colors green and blue.

BRAND NAME: Cialis

GENERIC NAME: tadalafil
BRAND NAME: Cialis

DRUG CLASS AND MECHANISM: Tadalafil is an oral drug that is used for treating impotence (the inability to attain or maintain a penile erection). It is in a class of drugs called phosphodiesterase inhibitors that also includes sildenafil (Viagra) and vardenafil (Levitra).

Erection of the penis is caused by the filling of the penis with blood. Filling occurs because the blood vessels that bring blood to the penis increase in size and deliver more blood to the penis, and, at the same time, the blood vessels that take blood away from the penis decrease in size and remove less blood from the penis.

Sexual stimulation that leads to an erection causes the production and release of nitric oxide in the penis. The nitric oxide causes an enzyme, guanylate cyclase, to produce cyclic guanosine monophosphate (cGMP). It is the cGMP that is primarily responsible for increasing and decreasing the size of the blood vessels carrying blood to and from the penis, respectively, and causing the erection. When the cGMP is destroyed by another enzyme, phosphodiesterase-5, the blood vessels return to their normal size, blood leaves the penis, and the erection ends. Tadalafil prevents phosphodiesterase-5 from destroying cGMP so that cGMP stays around longer. The persistence of cGMP leads to a more prolonged engorgement of the penis with blood.

Tadalafil was approved by the FDA in November, 2003.

PRESCRIPTION: Yes.

GENERIC AVAILABLE: No.

PREPARATIONS: Tablets: 5, 10, and 20 mg.

STORAGE: Store at room temperature between 15-30°C (59-86°F).

PRESCRIBED FOR: Tadalafil is used for the treatment of impotence.

DOSING: For most individuals, the recommended starting dose of tadalafil is 10 mg per day taken before sexual activity. Depending on the adequacy of the response or side effects, the dose may be increased to 20 mg or decreased to 5 mg a day. The effect of tadalafil may last up to 36 hours. Individuals who are taking medications that increase the blood levels of tadalafil should not exceed a total dose of 10 mg in 72 hours (See drug interactions). Tadalafil may be taken with or without food since food does not affect its absorption from the intestine.

DRUG INTERACTIONS: The breakdown and elimination of tadalafil from the body may be decreased by erythromycin, ketoconazole (Nizoral), itraconazole (Sporanox), indinavir (Crixivan) and ritonavir (Norvir). Therefore, these drugs may increase the levels of tadalafil in the blood. If these drugs are being used at the same time as tadalafil, the dose of tadalafil should be reduced in order to avoid side effects from high levels of tadalafil.

Tadalafil exaggerates the increases in heart rate and lowering of blood pressure caused by nitrates, e.g. nitroglycerin, isosorbide dinitrate (Isordil), isosorbide mononitrate (Imdur, Ismo, Monoket), nitroglycerin (Nitro-Dur, Transderm-Nitro) that are used primarily for treating heart pain (angina). In patients who take nitrates for angina, tadalafil could cause heart pain or possibly even a heart attack by exaggerating the increase in heart rate and the lowering of blood pressure. Therefore, tadalafil should not be used with nitrates. Tadalafil also exaggerates the blood pressure lowering effects of some alpha-blocking drugs e.g., terazosin (Hytrin) that primarily are used for treating high blood pressure or enlargement of the prostate. Individuals who take these alpha-blockers should be on a stable dose of the alpha-blocker before tadalafil is started. In such situations, tadalafil should be started at the lowest dose. If the patient is already taking tadalafil, the alpha-blocker should be started at the lowest dose. Tadalafil and alcohol both lower blood pressure. Therefore, combining tadalafil with alcohol may cause excessive drops in blood pressure and cause dizziness, headaches and increased heart rate.

PREGNANCY: Tadalafil is not approved for use in women.

NURSING MOTHERS: Tadalafil has not been evaluated in women who are breastfeeding.

SIDE EFFECTS: The most common side effects of tadalafil are facial flushing (reddening), headaches, stomach upset, diarrhea, flu-like symptoms and nausea. Tadalafil also may cause low blood pressure, blurred vision and changes in color vision, and abnormal ejaculation. Tadalafil has been associated with prolonged erections or priapism (painful erections lasting more than 6 hours). Patients should seek immediate medical help if they experience an erection lasting more than 4 hours. Use of tadalafil, most often in patients with pre-existing heart disease, has been associated with chest pain, heart attacks, death, strokes, palpitations and increased heart rate; however, it is not clear whether these side effects are due to tadalafil, concurrent use of nitrates, or the sexual activity itself.

Viagra Does Not Decrease Fertility says Pfizer

In response to recent studies indicating that Viagra reduces a man's fertility, Pfizer announced that it does not reduce a man's fertility. Daniel Watts, Pfizer's spokesman told Reuters "There's no evidence that Viagra decreases fertility in men. There have been many clinical trials as well as use by 23 million men in six years of use around the world, and there's been no evidence that Viagra affects fertility, so we don't put a lot of stock in that study."

According to recent research, Viagra makes the male sperm release an enzyme which allows it to break through the egg membrane too early. By the time it reaches the egg it cannot get in - hence, it becomes useless. The research was carried out at Queens University, Belfast, UK. The researchers said they found their findings 'worrying'.

Viagra is a blockbuster selling drug. Last year sales reached $1.9 billion. It is used to treat erectile dysfuntion (impotence - inability or difficulty in getting an erection for men).

The Belfast team said that men intending to start a family should be careful.

The team only looked at Viagra - not its rivals, such as Levitra and Cialis. These drugs work in similar ways to Viagra.

Pfizer said this is only one study, it was not carried out on humans. Pfizer said it was basically a test tube study.

The Pfizer spokesman went on to tell Reuters "Viagra has helped some men actually father children, helped aid in the fertility of men who have severe erectile dysfunction."

Conclusion by Editor of Medical News Today

Maybe more studies are needed - on humans. Anyway, Viagra should only be used with men who have erectile dysfunction problems. Other men who use Viagra are using it as a recreational drug - the drug is not intended as a recreational drug. Very impotent men, as the Pfizer spokesman said, have serious fertility problems anyway - Viagra has helped them have a sex life a again - without a sex life there is no fertility.