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sildenafil citrate
Viagra

Pregnancy Risk Category B

How supplied
Tablets:
25 mg, 50 mg, 100 mg

Action
Has no direct relaxant effect on isolated human corpus cavernosum, but enhances effect of nitric oxide (NO) by inhibiting phosphodiesterase type 5 (PDE5), which is responsible for degradation of cyclic guanosine monophosphate (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.

Indications & dosage
Erectile dysfunction--

Adults under age 65:
50 mg P.O., p.r.n., about 1 hour before sexual activity. Dosage range is 25 to 100 mg based on effectiveness and toleration. Maximum is one dose daily.
Elderly (ages 65 and older):
25 mg P.O., p.r.n., about 1 hour before sexual activity. Dosage may be adjusted based on patient response. Maximum is one dose daily.
Adjust-a-dose:
For adults with hepatic or severe renal impairment: 25 mg P.O. about 1 hour before sexual activity. Dosage may be adjusted based on patient response. Maximum is one dose daily.

Adverse reactions
CNS:
anxiety, headache, dizziness, seizures, somnolence, vertigo.
CV:
MI, sudden cardiac death, ventricular arrhythmias, cerebrovascular hemorrhage, transient ischemic attack, hypertension, flushing.
EENT:
diplopia, temporary vision loss, decreased vision, ocular redness or bloodshot appearance, increased intraocular pressure, retinal vascular disease, retinal bleeding, vitreous detachment or traction, paramacular edema, photophobia, color-tinged vision, blurred vision, ocular burning, swelling, pressure.
GI:
dyspepsia, diarrhea.
GU:
hematuria, prolonged erection, priapism, urinary tract infection.
Musculoskeletal:
arthralgia, back pain.
Respiratory:
respiratory tract infection.
Skin:
rash.
Other:
flulike syndrome.

Interactions
Drug-drug.
Beta blockers, loop and potassium-sparing diuretics: increased blood levels of major metabolite of sildenafil, N-desmethyl sildenafil. Clinical significance of these interactions isn't known. Monitor patient.
CYP3A4 inducers, rifampin:
reduced sildenafil plasma levels. Monitor effect.
Hepatic isoenzyme inhibitors (such as cimetidine, erythromycin, itraconazole, ketoconazole):
may reduce clearance of sildenafil. Avoid concomitant use.
Nitrates:
sildenafil enhances hypotensive effects. Don't use together.
Drug-food.
High-fat meal: reduced rate of absorption and decreased peak serum levels. Separate administration time from meals.

Effects on diagnostic tests
None reported.

Contraindications
Contraindicated in patients with hypersensitivity to drug or its components and in those with underlying CV disease. Concomitant use of organic nitrates at any frequency and in any form is also contraindicated.

Nursing considerations

Patient teaching

*Liquid contains alcohol. **May contain tartrazine.  †Canada  ‡Australia  §U.K.  OTCOver the counter
Reactions may be common, uncommon, life-threatening, or COMMON AND LIFE-THREATENING

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