What is tadalafil, and how does it work (mechanism of action)?

Tadalafil is an oral drug that is used for treating impotence (the inability to attain or maintain a penile erection) and benign prostatic hyperplasia (BPH). It is in a class of drugs called phosphodiesterase-5 (PDE5) 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 cGMP that is primarily responsible for increasing and decreasing the size of blood vessels carrying blood to and from the penis, respectively, and causing an 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.

The mechanism whereby tadalafil improves the symptoms of BPH is not clear, but phosphodiesterase-5 also is present in the muscles of the bladder and the prostate, and it has been suggested that the relaxation of these muscles may make the passage of urine less difficult, for example, by reducing the pressure in the muscle surrounding the opening to the urethra that controls the flow of urine from the bladder. Tadalafil was approved by the FDA in November 2003.

What brand names are available for tadalafil?

Adcirca, Cialis

Is tadalafil available as a generic drug?

GENERIC AVAILABLE: No

Do I need a prescription for tadalafil?

Yes

What are the uses for tadalafil?

Tadalafil is used for the treatment of impotence (erectile dysfunction, ED) and benign prostatic hyperplasia. Tadalafil offers no protection against sexually transmitted diseases.

What are the side effects of tadalafil?

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.

What is the dosage for tadalafil?

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.

Which drugs or supplements interact with tadalafil?

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).

Is tadalafil safe to take if I'm pregnant or breastfeeding?

: Tadalafil is not approved for use in women.

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

What else should I know about tadalafil?

What preparations of tadalafil are available?

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

How should I keep tadalafil stored?

Tadalafil should be stored at room temperature between 15 C to 30 C (59 F to 86 F).