No

Phosphodiesterase Enzyme Inhibitor

Treatment of erectile dysfunction

B

In patients with a known hypersensitivity to any component of the tablet; has been shown to potentiate the hypotensive effects of nitrates, and its administration to patients who are concurrently using organic nitrates in any form is contraindicated

There is a degree of cardiac risk associated with sexual activity; therefore, physicians may wish to consider the cardiovascular status of their patients prior to initiating any treatment for erectile dysfunction. Agents for the treatment of erectile dysfunction should be used with caution in patients with anatomical deformation of the penis (angulation, cavernosal fibrosis, or Peyronie's disease), or in patients who have conditions which may predispose them to priapism (sickle cell anemia, multiple myeloma, leukemia).

A minority of patients with retinitis pigmentosa have generic disorders of retinal phosphodiesterases. There is no safety information on the administration of sildenafil to these patients and sildenafil should be administered with caution.

>10%:

Central nervous system: Headache

Cardiovascular: Flushing

1% to 10%:

Central nervous system: Dizziness

Dermatologic: Rash

Gastrointestinal: Dyspepsia, diarrhea

Genitourinary: Urinary tract infection

Ocular: Abnormal vision

Respiratory: Nasal congestion

In studies with healthy volunteers of single doses up to 800 mg, adverse events were similar to those seen at lower doses but incidence rates were increased

CYP3A3/4 enzyme substrate (major); CYP2C9 enzyme substrate (minor)

Increased effect/toxicity: Cimetidine, erythromycin, ketoconazole, itraconazole, mibefradil, nitroglycerin, protease inhibitors. A reduction in sildenafil's dose is recommended when used with ritonavir, a protease inhibitor, (no more than 25 mg per dose; no more than 25 mg in 48 hours).

Decreased effect: Rifampin

Store tablets at controlled room temperature 15°C to 30°C (59°F to 86°F)

Does not directly cause penile erections, but affects the response to sexual stimulation. The physiologic mechanism of erection of the penis involves release of nitric oxide (NO) in the corpus cavernosum during sexual stimulation. NO then activates the enzyme guanylate cyclase, which results in increased levels of cyclic guanosine monophosphate (cGMP), producing smooth muscle relaxation and inflow of blood to the corpus cavernosum. Sildenafil enhances the effect of NO by inhibiting phosphodiesterase type 5 (PDE5), which is responsible for degradation of cGMP in the corpus cavernosum; when sexual stimulation causes local release of NO, inhibition of PDE5 by sildenafil causes increased levels of cGMP in the corpus cavernosum, resulting in smooth muscle relaxation and inflow of blood to the corpus cavernosum; at recommended doses, it has no effect in the absence of sexual stimulation.

Onset of action: ~60 minutes

Duration: 2-4 hours

Bioavailability: 40%

Protein binding: 96%

Half-life: 4 hours

Metabolism: Hepatic microsomal isoenzymes (CYP3A4 [major] and CYP2C9 [minor route])

Elimination: Feces (80%), urine (13%)

Adults: Oral: For most patients, the recommended dose is 50 mg taken as needed, approximately 1 hour before sexual activity. However, sildenafil may be taken anywhere from 30 minutes to 4 hours before sexual activity. Based on effectiveness and tolerance, the dose may be increased to a maximum recommended dose of 100 mg or decreased to 25 mg. The maximum recommended dosing frequency is once daily.

May cause dizziness

Useful for psychotropic-induced sexual dysfunction

No information available to require special precautions

No effects or complications reported

Inform prescriber of all other medications you are taking; serious side effects can result when sildenafil is used with nitrates and some other medications. Do not combine sildenafil with other approaches to treating erectile dysfunction without consulting prescriber. Note that sildenafil provides no protection against sexually transmitted diseases, including HIV. You may experience headache, flushing, or abnormal vision (blurred or increased sensitivity to light); use caution when driving at night or in poorly lit environments. Report immediately acute allergic reactions, chest pain or palpitations, persistent dizziness, sign of urinary tract infection, rash, respiratory difficulties, genital swelling, or other adverse reactions.

Tablet, as citrate: 25 mg, 50 mg, 100 mg

"Erythromycin (E-Mycin®) and Sildenafil (Viagra®)," in Hansten and Horn's Drug Interactions Analysis and Management, Seattle, WA: Applied Therapeutics, Inc, 1998, 2:3N109.