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Cialis (tadalafil) vs. Viagra (sildenafil)

Cialis (tadalafil) and Viagra (sildenafil) are oral drugs that are used for treating impotence (the inability to attain or maintain a penile erection) and benign prostatic hyperplasia (BPH). They are in a class of drugs called phosphodiesterase-5 (PDE5) inhibitors that also includes vardenafil (Levitra, Staxyn ODT), and avanafil (Stendra).

Penile erection is caused by the engorgement of the penis with 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. Cialis and Viagra inhibit an enzyme called phosphodiesterase-5 (PDE5) which destroys the cGMP. Thus, Cialis and Viagra prevent the destruction of cGMP and allows cGMP to accumulate and persist longer. The longer cGMP persists, the more prolonged the engorgement of the penis.

SLIDESHOW

What are the side effects of Cialis and Viagra?

Cialis

WARNING

If you are taking Cialis and you have nausea, chest pain or dizziness during sex, seek medical help immediately as you may have a life-threatening condition.

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,
  • changes in color vision, and
  • abnormal ejaculation.
  • Priapism, or an erection that lasts more than four hours that can damage the penis

Viagra

WARNING

If you are taking Viagra and you have nausea, chest pain or dizziness during sex, seek medical help immediately as you may have a life-threatening condition.

Approximately 15% of persons taking Viagra experience side effects. The most common side effects are:

  • facial flushing (1 in 10),
  • headaches (1 in 6),
  • stomach pain,
  • nasal congestion,
  • nausea,
  • dizziness,
  • rash,
  • urinary tract infections (UTIs)
  • diarrhea, and
  • an inability to differentiate between the colors green and blue.
  • Priapism, or an erection that lasts more than four hours that can damage the penis

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What is the dosage of Cialis vs. Viagra?

Cialis

For most individuals, the recommended starting dose of tadalafil is 10 mg per day taken before sexual activity (tadalafil for use as needed).

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). For once daily use without regard to sexual activity, the recommended dose is 2.5 to 5 mg daily. Tadalafil should not be taken more than once daily.

The recommended dose for BPH, or BPH and ED is 5 mg daily taken about the same time each day. Tadalafil may be taken with or without food since food does not affect its absorption from the intestine.

The dose of tadalafil may require adjustment for patients with reduced kidney or liver function.

Viagra

  • 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.

What drugs interact with Cialis and Viagra?

Cialis

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 to 10 mg every 72 hours when used as needed or 2.5 mg when used daily in order to avoid side effects from high levels of tadalafil.

Rifampin, carbamazepine (Tegretol, Tegretol XR, Equerto, Carbatrol), phenytoin (Dilantin, Dilantin-125), and phenobarbital may decrease blood levels of tadalafil, possibly reducing the effect of tadalafil.

Tadalafil exaggerates the increases in heart rate and lowering of blood pressure caused by nitrates, for example, 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 for example, terazosin (Hytrin) that primarily are used for treating high blood pressure or enlargement of the prostate (BPH). 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. Combining tadalafil with alpha-blockers for treatment of BPH is not recommended.

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.

PDE5 inhibitors may affect platelet function and therefore prolong bleeding. Tadalafil should be used cautiously in patients with bleeding disorders or active ulcers. Tadalafil should not be combined with Adcirca (another form of tadalafil) or other PDE5 inhibitors, for example, vardenafil (Levitra) or sildenafil (Viagra, Revatio).

Viagra

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.

Are Cialis and Viagra safe to use while pregnant and breastfeeding?

Cialis

Tadalafil is not approved for women and has not been evaluated in women who are breastfeeding.

Viagra

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.

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Summary

Cialis (tadalafil) and Viagra (sildenafil) are oral drugs that are used for treating impotence (the inability to attain or maintain a penile erection) and benign prostatic hyperplasia (BPH). They are in a class of drugs called phosphodiesterase-5 (PDE5) inhibitors that also includes vardenafil (Levitra, Staxyn ODT), and avanafil (Stendra).

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