Sildenafil Citrate

sildenafil citrate (sill den' ah fill) Viagra Pregnancy Category B Drug class

Impotence drug Therapeutic actions

Selectively inhibits cGMP-specific phosphodiesterase type 5. The mechanism of penile erection involves the release of nitric oxide into the corpus cavernosum of the penis during sexual stimulation. Nitrous oxide activates cGMP, which causes smooth muscle relaxation, allowing the flow of blood into the corpus cavernosum. Sildenafil prevents the breakdown of cGMP by phosphodiesterase, leading to increased cGMP levels and prolonged smooth muscle relaxation, promoting the flow of blood into the corpus cavernosum. Indication

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Treatment of erectile dysfunction in the presence of sexual stimulation Unlabeled use: Pulmonary hypertension, female sexual dysfunction

Contraindications and cautions

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Contraindicated with allergy to any component of the tablet, contraindicated for women or children; concomitant use of nitrates. Use cautiously with hepatic or renal dysfunction; with anatomical deformation of the penis; with known cardiac disease (effects of sexual activity need to be evaluated).

Available forms

Tablets—25, 50, 100 mg Dosages ADULTS

50 mg PO taken 1 hr before anticipated sexual activity; range 25–100 mg PO. May be taken 30 min–4 hr before sexual activity. Limit use to once per day. PEDIATRIC PATIENTS

Not intended for use in children. GERIATRIC PATIENTS

For patients > 65 yr, start dose at 25 mg PO. PATIENTS WITH RENAL OR HEPATIC IMPAIRMENT

Patients with hepatic impairment or creatinine clearance < 30 mL/min may have increased serum levels; start dose at 25 mg PO. Pharmacokinetics Route Oral

Onset Rapid

Peak 30–120 min

Metabolism: Hepatic; T1/2: 4 hr Distribution: Not intended for use in women, no clear studies on crossing the placenta or entering breast milk Excretion: Feces and urine Adverse effects

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CNS: Headache, abnormal vision, dizziness, nasal congestion CV: Flushing GI: Dyspepsia, diarrhea Other: Urinary tract infection, rash

Interactions

Drug-drug • Possible severe hypotension and serious cardiac events if combined with nitrates; this combination must be avoided • Possible increased sildenafil levels and effects if taken with cimetidine, amlodipine, erythromycin, protease inhibitors; monitor patient and reduce dosage as needed Drug-food • Decreased rate of absorption and onset of action if taken with a high-fat meal • Decreased metabolism and risk of toxic effects if combined with grapefruit juice; avoid this combination Nursing considerations Assessment

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History: Allergy to any component of the tablet; hepatic or renal dysfunction; with anatomical deformation of the penis, known cardiac disease; concomitant use of nitrates Physical: Orientation, affect; skin color, lesions; P, BP, ECG, renal and hepatic function tests

Interventions

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Ensure diagnosis of erectile dysfunction and determine underlying causes and other appropriate treatment. Advise patient that drug does not work in the absence of sexual stimulation. Limit use to once per day. Remind patient that drug does not protect against sexually transmitted diseases and appropriate measures should be taken. Advise patient to never take this drug with nitrates; serious and even fatal complications can occur. Advise patients receiving HIV medications that there is an increased risk of sidenafil-associated adverse drug reactions, including hypotension, visual changes, and priapism. Do not exceed 25 mg of sildenafil in 48 hr.

Teaching points

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Take this drug 30 min to 4 hr before anticipated sexual activity. The usual timing is 1 hr. The drug will have no effect in the absence of sexual stimulation. Onset of drug effects will be slowed if taken with a high-fat meal; plan accordingly. Avoid drinking grapefruit juice if using this drug. This drug will not protect you from sexually transmitted diseases; use appropriate precautions. Do not take this drug if you are taking any nitrates; serious side effects and even death can occur. These side effects may occur: Headache, dizziness, rash, flushing. Report difficult or painful urination, rash, dizziness, palpitations.

Adverse effects in Italic are most common; those in Bold are life-threatening.