Sildenafil citrate
Sildenafil citrate (Viagra)
Sildenafil citrate
(sill- DEN-ah-fill)
Pregnancy Category: B Viagra (Rx)

Classification: Drug for erectile dysfunction

Action/Kinetics: Nitric oxide activates the enzyme guanylate cyclase, which causes increased levels of guanosine monophosphate (cGMP) and subsequently smooth muscle relaxation in the corpus cavernosum and allowing inflow of blood. Sildenafil enhances effect of nitric oxide by inhibiting phosphodiesterase type 5 which is responsible for degradation of cGMP in the corpus cavernosum. When sexual stimulation causes local release of nitric oxide, inhibition of phosphodiesterse type 5 by sildenafil causes increased levels of cGMP in the corpus cavernosum and thus smooth muscle relaxation and inflow of blood resulting in an erection. Drug has no effect in absence of sexual stimulation. Rapidly absorbed after PO use. Absorption is decreased when taken with high fat meal. Metabolized in liver where it is converted to active metabolite (N-desmethyl sildenafil). t 1/2, sildenafil and metabolite: 4 hr. Excreted mainly in feces (80%) with about 13% excreted in urine. Reduced clearance is seen in geriatric clients.

Uses: Treatment of erectile dysfunction. Has no effect in the absence of sexual stimulation.

Contraindications: Concomitant use with organic nitrates in any form or with other treatments for erectile dysfunction. Use in men for whom sexual activity is not advisable due to underlying cardiovascular status. Use in newborns, children, or women.

Special Concerns: Use with caution in clients with anatomical deformation of penis, in those with predisposition to priapism (e.g., sickle cell anemia, multiple myeloma, leukemia), in bleeding disorders or active peptic ulceration, and in those with genetic disorders of retinal phosphodiesterases. Drug is potentially hazardous in those with acute coronary ischemia but not on nitrates; have CHF, borderline low BP, or borderline low volume status; are on complicated antihypertensive therapy with several drugs; are taking erythromycin or cimetidine; or have impaired hepatic or renal function.

Side Effects: CNS: Headache, dizziness, ataxia, hypertonia, neuralgia, neuropathy, paresthesia, tremor, vertigo, depression, insomnia, somnolence, abnormal dreams, decreased reflexes, hypesthesia, seizures, anxiety. GI: Dyspepsia, diarrhea, vomiting, glossitis, colitis, dysphagia, gastritis, gastroenteritis, esophagitis, stomatitis, dry mouth, rectal hemorrhage, gingivitis. CV: Hypertension, TIA, MI, sudden cardiac death, ventricular arrhythmia, CVA especially with preexisting CV risk factors. Also, angina pectoris, AV block, migraine, syncope, tachycardia, palpitation, hypotension, postural hypotension, myocardial ischemia, cerebral thrombosis, cardiac arrest, heart failure, cardiomyopathy, abnormal ECG. Dermatologic: Flushing, rash, urticaria, herpes simplex, pruritus, sweating, skin ulcer, contact dermatitis, exfoliative dermatitis. GU: UTI, cystitis, nocturia, urinary frequency, urinary incontinence, abnormal ejaculation, genital edema and anorgasmia, prolonged erection, priaprism, hematuria, breast enlargment. Ophthalmic: Mild and transient predominantly color tinge to vision, increased sensitivity to light, blurred vision, mydriasis, conjunctivitis, photophobia, eye pain, eye hemorrhage, cataract, dry eyes, diplopia, temporary vision loss, ocular redness or bloodshot appearance, ocular burning, ocular swelling/pressure, increased intraocular pressure, retinal vascular disease or bleeding, vitreous detachment/traction, paramacular edema. Otic: tinnitus, deafness, ear pain. Respiratory: Nasal congestion, respiratory tract infection, asthma, dyspnea, laryngitis, pharyngitis, sinusitis, bronchitis, increased sputum, increased cough. Musculoskeletal: Arthritis, arthrosis, myalgia, tendon rupture, tenosynovitis, bone pain, myasthenia, synovitis. Miscellaneous: Back pain, flu syndrome, face edema, shock, asthenia, pain, chills, accidental fall/injury, abdominal pain, allergic reaction, chest pain. NOTE: Death has occurred in some clients following use of the drug.

Laboratory Test Alterations: Abnormal LFTs.

Overdose Management: Symptoms: Extension of side effects. Treatment: Standard supportive measures.

Drug Interactions: Amlodipine / Additional in BP Cimetidine / Sildenafil plasma levels Erythromycin / Significant sildenafil plasma levels Itraconazole / Sildenafil plasma levels Ketoconazole / Sildenafil plasma levels Mibefradil / Sildenafil plasma levels Nitrites / Potentiation of vasodilatory effects significant and potential fatal BP; do not use together Rifampin / Sildenafil plasma levels

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

Dosage
?Tablets Treat erectile dysfunction.
For most clients, 50 mg no more than once daily, as needed, about 1 hr before sexual activity. Take anywhere from 0.5 hr to 4 hr before sexual activity. Depending on tolerance and effectiveness, dose may be increased to maximum of 100 mg or decreased to 25 mg. Consider a starting dose of 25 mg in those with hepatic or renal impairment, in geriatric clients, or if taken with erythromycin, itraconzole, or ketoconazole.