avanafil

Avanafil is an oral drug that is used for treating impotence (the inability to attain or maintain a penile erection), also known as erectile dysfunction (ED). It is in a class of drugs called phosphodiesterase inhibitors, which also includes tadalafil (Cialis), 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. Avanafil 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.

Avanafil was approved by the FDA in April 2012.

The most common side effects of avanafil are:

• facial flushing (reddening),
• headaches,
• back pain,
• nasal congestion,
• dizziness, and
• upper respiratory tract infections.
• diarrhea,
• nausea, and
• flu-like symptoms

Avanafil also may cause low blood pressure, blurred vision and changes in color vision, and abnormal ejaculation. Avanafil may cause 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 avanafil, especially in patients with pre-existing heart disease, may cause

• chest pain,
• heart attacks,
• death,
• strokes,
• palpitations, and
• increased heart rate.

Rare cases of sudden loss of hearing have been reported with phosphodiesterase inhibitors such as avanafil, sometimes associated with ringing in the ears and dizziness. If changes in hearing occur, patients should stop their avanafil and seek immediate medical attention. Phosphodiesterase-5 inhibitors have been associated rarely with non-arteritic anterior ischemic optic neuropathy (NAION), a condition which causes decreased vision and may lead to blindness.

• For most individuals, the recommended starting dose of avanafil is 100 mg per day taken about 30 minutes before sexual activity.
• Depending on the adequacy of the response or side effects, the dose may be increased to 200 mg or decreased to 50 mg a day.
• Individuals who are taking medications that moderately increase the blood levels of avanafil should not exceed a total dose of 50 mg in 24 hours 

• The breakdown and elimination of avanafil from the body may be decreased by several drugs, leading to increased blood levels of avanafil and possible toxicity. Ketoconazole (Nizoral), itraconazole (Sporanox), indinavir (Crixivan) and ritonavir (Norvir), atazanavir (Reyataz), clarithromycin (Biaxin), nelfinavir (Viracept), saquinavir (Invirase), telithromycin (Ketek) profoundly increase blood levels of avanafil and should not be combined with avanafil.
• The dose of avanafil should not exceed 50 mg daily when combined with erythromycin, amprenavir (Agenerase), aprepitant (Emend), diltiazem (Cardizem), fluconazole (Diflucan), fosamprenavir (Lexiva), and verapamil (Calan) because these drug moderately increase blood levels of avanafil.
• Avanafil 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), and nitroglycerin (Nitro-Dur, Transderm-Nitro) that are used primarily for treating heart pain (angina). In patients who take nitrates for angina, avanafil could cause heart pain or possibly even a heart attack by exaggerating the increase in heart rate and the lowering of blood pressure. Therefore, avanafil should not be used with nitrates. If nitrates must be administered to a patient who has taken avanafil, at least 12 hours should elapse after the last dose of avanafil before administering the nitrates.
  • Avanafil 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. Individuals who take these alpha-blockers should be on a stable dose of the alpha-blocker before avanafil is started. In such situations, avanafil should be started at the 50 mg dose. If the patient is already taking avanafil, the alpha-blocker should be started at the lowest dose.
• Avanafil and alcohol both lower blood pressure. Therefore, combining avanafil with alcohol may cause excessive drops in blood pressure and cause dizziness, headaches, and increased heart rate.
• Avanafil should not be combined with other PDE5 inhibitors used for treating impotence, for example, vardenafil (Levitra) or sildenafil (Viagra, Revatio).

• Avanafil is not approved for use in women.
• Avanafil is not approved for women and has not been evaluated in women who are breastfeeding.

What preparations of avanafil (Stendra) are available?

• Tablets: 50, 100, and 200 mg.

How should I keep avanafil (Stendra) stored?

• Avanafil should be stored at room temperature between 20 C and 25 C (68 F and 77 F).