What is avanafil (Stendra), and how does it work (mechanism of action)?
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 that 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.
What brand names are available for avanafil (Stendra)?
Stendra
Is avanafil (Stendra) available as a generic drug?
GENERIC AVAILABLE: No.
Do I need a prescription for avanafil (Stendra)?
Yes.
What are the side effects of avanafil (Stendra)?
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.
What is the dosage for avanafil (Stendra)?
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 (See drug interactions).
Which drugs or supplements interact with avanafil (Stendra)?
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).
QUESTION
Erectile dysfunction (ED) is…
See Answer
Is avanafil (Stendra) safe to take if I’m pregnant or breastfeeding?
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 else should I know about avanafil (Stendra)?
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).
