Sildenafil
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4-ethoxyphenyl]sulfonyl]-4-methylpiperazine citrate
Viagra: Administer orally ~1 hour before sexual activity
Brand/Trade Names of Drug
Viagra®, Revatio™
Generic Name of Drug
Sildenafil (sil DEN a fil) 
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Description
Sildenafil is a selective phosphodiesterase-5 enzyme inhibitor (PDE5), similiar to vardenafil and tadalafil. It is administered orally for the treatment of male erectile dysfunction (ED) and pulmonary arterial hypertension (PAH). Sildenafil is the first agent of its class to be approved and marketed for the treatment of ED in 1998. Orginally it was developed for treatment of angina, but was later found to be effective for the treatment of ED. Sildenafil was approved for treatment of PAH in 2005. [1] [2] [3] [4]
Mechanism of action
Erectile dysfunction: 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 in the corpus cavernosum and allowing inflow of blood. Sildenafil has no direct relaxant effect on isolated human corpus cavernosum, but enhances the effect of nitric oxide (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. Sildenafil at recommended doses has no effect in the absence of sexual stimulation.[1]
Pulmonary arterial hypertension (PAH): Sildenafil is an inhibitor of cGMP specific phosphodiesterase type-5 (PDE5) in the smooth muscle of the pulmonary vasculature, where PDE5 is responsible for degradation of cGMP. Sildenafil, therefore, increases cGMP within pulmonary vascular smooth muscle cells resulting in relaxation. In patients with pulmonary hypertension, this can lead to vasodilation of the pulmonary vascular bed and, to a lesser degree, vasodilatation in the systemic circulation. [2]
Time Required for Therapeutic Response
Pharmacokinetics
Absorption
Sildenafil is rapidly absorbed. Maximum observed plasma concentrations are reached within 30 to 120 minutes of oral dosing in the fasted state. When Sildenafil is taken with a high fat meal, the rate of absorption if reduced, with a mean delay in tmax of 60 minutes and a mean reduction in Cmax of 29%.[1]
Distribution
The mean steady state volume of distribution (Vss) for sildenafil is 105 L, indicating distribution into the tissues. Sildenafil and its major circulating N-desmethyl metabolite are both approximately 96% bound to plasma proteins. Protein binding is independent of total drug concentrations.[1]
Metabolism
Sildenafil has an absolute bioavailability of about 40% after oral administration. It is eliminated predominantly by hepatic metabolism, CYP3A4 and is converted to an active metabolite with properties similar to the parent..[1]
Excretion
Sildenafil is excreted as metabolites predominantly in the feces (80%) and urine (13%)..[1]
Special Population Pharmacokinetics
- Renal insufficiency
In volunteers with severe (ClCr=<30 mL/min) renal impairment, sildenafil clearance was reduced, resulting in approximately doubling of AUC and Cmax compared to age-matched volunteers with no renal impairment.
- Hepatic insufficiency
In volunteers with hepatic cirrhosis (Child-Pugh A and B), sildenafil clearance was reduced, resulting in increases in AUC (84%) and Cmax (47%) compared to age-matched volunteers with no hepatic impairment.
- Geriatric
Healthy elderly volunteers (65 years or over) had a reduced clearance of sildenafil, with free plasma concentrations approximately 40% greater than those seen in healthy younger volunteers (18-45 years)
- Gender
Sildenafil for treatment of ED is only indicated for males
Indications
FDA Approved Indications
Non-FDA Approved Indications
- Raynaud's Phenomenon [13]
Dosage
- Erectile Dysfunction
- Maintenance Dose: 25 to 100 mg/day
- Pulmonary Artery Hypertension
- Maintenance Dose: 20mg 3 times a day, take 4 to 6 hours part
- Maximum Dosage Limits
- Adults: 100 mg/day
- Elderly: (>65) Initial dose of 25 mg/day
- Dosage Adjustment
- Renal insufficiency: CrCl ≤ 30ml/min : Initial dose of 25 mg/day
- Hepatic insufficiency: Initial dose of 25 mg/day
- Hemodialysis: Safety and efficacy have not been studied in patients with end-stage renal disease requiring dialysis.
- Geriatric: Initial dose of 25 mg/day.
- Pediatric: Not indicated for this patient population.
- Gender: No dosage adjustments needed (Viagra® is indicated for males only)
Administration
- Route: Oral
- Method: Swallow tablet followed by a drink of water
- Special considerations:
- Revatio™: Should take tablets at least 4 to 6 hours apart.
- Viagra®: Should be taken ~ 1 hour before sexual activity.
Monitoring Parameters
- No laboratory monitoring parameters necessary.
- Monitor for response and adverse reactions.
Contraindications/Precautions
Contraindications
- Sildenafil has shown to potentiate the hypotensive effects of nitrates, and its administration in patients who are using nitrates of any form, either regularly and/or intermittently, is contraindicated. A minimum of 24 hours must pass before nitrates can be used to relieve angina or other potentially life-threatening cardiovascular situations.
- Sildenafil is contraindicated for patients with a known hypersensitivity to sildenafil or any component of the tablet.
Warnings
- FDA notified healthcare professionals of updated labeling for Cialis®, Levitra®, and Viagra® to reflect a small number of post-marketing reports of sudden vision loss, attributed to NAION (non arteritic ischemic optic neuropathy), a condition where blood flow is blocked to the optic nerve. FDA advises patients to stop taking these medicines, and call a doctor or healthcare provider right away if they experience sudden or decreased vision loss in one or both eyes. Patients taking or considering taking these products should inform their health care professionals if they have ever had severe loss of vision, which might reflect a prior episode of NAION. Such patients are at an increased risk of developing NAION again. At this time, it is not possible to determine whether these oral medicines for erectile dysfunction were the cause of the loss of eyesight or whether the problem is related to other factors such as high blood pressure or diabetes, or to a combination of these problems.FDA Medwatch
- Cardiovascular Effects
- General: In men with certain underlying cardiovascular conditions, treatment for erectile dysfunction, including sildenafil is not recommended; there is a degree of cardiac risk associated with sexual activity.
- Left Ventricular Outflow Obstruction: Patients with left ventricular outflow obstruction (e.g. aortic stenosis) can be sensitive to the vasodilating affects of PDE5 inhibitors.
- Sildenafil can decrease supine blood pressure in healthy male patients by 8.4 mmHg in systolic and 5.5 mmHg in diastolic due to its systemic vasodilatory properties. Caution in patients with underlying cardiovascular diseases which can be adversely affected.
- Concomitant therapy with potent CYP 3A4 Inhibitors
- Patient populations not studied in clinical trials; Due to the lack of controlled clinical data on the safety and efficacy of Viagra in the following patients, prescribe with caution.
- Patients with unstable angina; hypotension (resting systolic blood pressure of <90mmHg); uncontrolled hypertension (>170/110 mmHg); recent history (within 6 months) of stroke, life-threatening arrhythmia, or MI; severe cardiac failure
- Patients with retinitis pigmentosa
- Prolonged erection greater than 4 hours and priapism (painful erections greater than 6 hours in duration) have been reported. In such an event, patient should seek immediate medical assistance. If priapism is untreated in a timely matter, penile tissue damage and permanent loss of potency could result.
Precautions
- Alpha-blockers: caution with co-administration with PDE5 inhibitors; both agents are vasodilators with blood-pressure lowering effects. When used in combination, potential for additive effect on significantly lowering blood pressure leading to symptomatic hypotension (e.g. fainting, lightheadedness, dizziness).
- Viagra® should be used with caution in patients with anatomical deformation of the penis, or in patients who have conditions which may predispose them to priapism; sickle cell anemia, multiple myeloma, or leukemia.
Pregnancy indications
- Pregnancy category: B. Viagra® is not indicated for use in newborns, children, or women.
- Teratogenicity: No evidence of teratogenicity
Breast-feeding indications
- Secretion into breast milk: There are no adequate and well-controlled studies of sildenafil in pregnant women.
Drug-Drug Interactions
Severity Level | Increased Effect/Toxicity | Decreased Effect | |
|---|---|---|---|
| 4 | Organic Nitrates[1][17]  | Not known | |
| 3 | Protease Inhibitors[18][19] Alpha1-Blockers[20] [21] Antifugal Agents(Imidazole)[1][22] Macrolide Antibiotics[1] Cimetidine[1][23] CYP 3A4 Inhibitors[1] | Not known | |
| 2 | Fluvoxamine[24] | CYP 3A4 Inducers[1] Bosentan[25]
| |
| 1 | Not known | Not known |
Drug-Food-Herb Interactions
| Severity Level | Increased Effect/Toxicity | Decreased Effect | |
|---|---|---|---|
| 4 | Not known | Not known | |
| 3 | Not known | High-Fat Meals [1]
| |
| 2 | Grapefruit Juice [1] | Not known | |
| 1 | Not known | Not known |
Adverse Reactions/Side Effects
Over 3700 patients (ages 19-87) worldwide have been included in clinical trials with Viagra®. Of those patients, more than 550 were on treatment for ≥ 1 year. In placebo-controlled clinical trials, the rate of discontinuation due to an adverse event(s) for the Viagra® was not significantly different compared to placebo, 2.5% and 2.3%, respectively. The adverse events reported from the trials were similar and generally transient and mild to moderate in nature. The prevalence of adverse events associated with increased doses.[1]
| Incidence | Body System | Adverse Reactions |
|---|---|---|
| > 10 % | All | Headache (16%), Dyspepsia (7-17%), Flushing (10%), Abnormal Vision (3-11%) |
| 2-10% | CNS | Dizziness (2%) |
| Dermatologic | Rash (2%) | |
| GI | Diarrhea (3%) | |
| GU | Urinary Tract Infection (3%) | |
| Neuromuscular & skeletal | Arthralgia | |
| Respiratory | Nasal Congestion (4%), Respiratory Tract Infection | |
| Misc | Flu Syndrome | |
| < 2% | All | abdominal pain, abnormal dreams, abnormal ejaculation, abnormal electrocardiogram, accidental fall, accidental injury, allergic reaction, anemia, angina pectoris, anorgasmia, anxiety, arthritis, arthrosis, asthenia, asthma, ataxia, AV block, bone pain, breast enlargement, bronchitis, cardiac arrest, cardiomyopathy, cataract, cerebral thrombosis, cerebrovascular hemorrhage, chest pain, chills, conjunctivitis, colitis, contact dermatitis, cough increased, cystitis, deafness, depression, diplopia, dry eyes, dry mouth, dysphagia, dyspnea, ear pain, edema, epistaxis, esophagitis, exfoliative dermatitis, eye hemorrhage, eye pain, face edema, gastroenteritis, genital edema, gingivitis, glossitis, gout, heart failure, hematuria, herpes simplex, hypertension, hypesthesia, hypoglycemic reaction, hypotension, hyperglycemia, hypernatremia, hypertonia, hyperuricemia, increased intraocular pressure, intracerebral hemorrhages, insomnia, laryngitis, leukopenia, liver function tests abnormal, migraine, myalgia, myasthenia, mydriasis, myocardial infarction, myocardial ischemia, neuralgia, neuropathy, nocturia, non-arteritic anterior ischemic optic neuropathy, ocular burning, ocular redness or bloodshot appearance, ocular swelling/pressure, pain, palpitation, paramacular edema, peripheral edema, pharyngitis, photophobia, photosensitivity reaction, postural hypotension, priapism, prolonged erection, pruritus, pulmonary hemorrhage, rectal hemorrhage, reflexes decreased, retinal vascular disease or bleeding, seizure, shock, sinusitis, skin ulcer, somnolence, sputum increased, stomatitis, subarachnoid hemorrhages, sudden cardiac death, sweating, syncope, synovitis, tachycardia, temporary vision loss/decreased vision, tendon rupture, tenosynovitis, thirst, tinnitus, transient ischemic attack, tremor, urinary frequency, urinary incontinence, urticaria, ventricular arrhythmia, vertigo, vitreous detachment/traction, and vomiting. |
The safety data was obtained from 277 patients treated for pulmonary arterial hypertension from the pivotal study and from an open-label extension study. The rate of discontinuation due to an adverse event was not significantly different for Revatio™ (dosed at 20mg tid) compared to placebo, 3% and 3%, respectively. In the pivotal placebo-controlled trial, patient reports of adverse event greater than 3% were significantly greater for Revatio™ compared to placebo. Adverse events were generally transient and mild to moderate in nature.[2]
| Incidence | Body System | Adverse Reactions |
|---|---|---|
| > 10 % | All | Headache(7-46%), Dyspepsia(6-13%), Flushing (6-10%) |
| 2-10% | CNS | Insomnia (7%), Pyrexia (6%), |
| Dermatologic | Erythema (6%) | |
| GI | Diarreha (9%), Gastritis (3%) | |
| Neuromuscular & skeletal | Myalgia (7%), Paresthesia (3%) | |
| Respiratory | Dyspnea exacerbated (7%), Rhinitis (4%), Sinusitis (3%) | |
| Misc | Epistaxis (9%) | |
| < 2% | All | See Viagra® |
Overdosage Measures
Studies with healthy volunteers found that with single doses up to 800 mg, adverse events were similar to those seen at lower doses but prevalence was increased. In cases of overdose, standard supportive measures should be adopted as required.[1]
Product Information and Distribution
| Name | Manufacturer | Dosage Form | Strength | Quantity | NDC | Storage | Markings |
|---|---|---|---|---|---|---|---|
| Viagra [1] | Pfizer | Oral Tablets | 25 mg | 30 | 00069-4200-30 | 15-30°C (59-86°F) | PFZIER/VGR25 |
| 100 | NA | ||||||
| 50 mg | 30 | 00069-4210-30 | PFZIER/VGR50 | ||||
| 100 | 00069-4210-66 | ||||||
| 100 mg | 30 | 00069-4220-30 | PFZIER/VGR50 | ||||
| 100 | 00069-4220-66 |
| Name | Manufacturer | Dosage Form | Strength | Quantity | NDC | Storage | Markings |
|---|---|---|---|---|---|---|---|
| Revatio[2] | Pfizer | Oral Tablets | 20 mg | 90 | 00069-4190-68 | 15-30°C (59-86°F) | RVT20 |
Manufacturers/Distributors
Inactive ingredients
- Viagra®
Microcrystalline Cellulose, Anhydrous Dibasic Calcium Phosphate, Croscarmellose Sodium, Magnesium Stearate, Hypromellose, Lactose, Titanium Dioxide, Triacetin, and FD & C Blue #2 Aluminum Lake.
- Revatio™
Microcrystalline Cellulose, Anhydrous Dibasic Calcium Phosphate, Croscarmellose Sodium, Magnesium Stearate, Hypromellose, Titanium Dioxide, Lactose, Triacetin
Pharmacogenomic information
Sildenafil Pharmacogenomic Information
Patient Information
- May take with or without food.
- Avoid high-fat meals; onset of action occurs faster with an empty stomach.
- Should be taken approximately 60 minutes before sexual activity.
- Sexual stimulation is required for an erection to occur after taking sildenafil.
- Sildenafil provides no protection against sexually-transmitted diseases.
- In the event that an erection persists longer than 4 hours, the patient should seek immediate medical assistance. If not treated promptly, irreversible damage to the erectile tissue may result.
- Patients should be advised to contact their healthcare provider for dose modification if they are not satisfied with the quality of their sexual performance with sildenafil or in the case of an unwanted effect.
- Side effects are usually mild and transient-headache, flushing, gastrointestinal upset.
- Avoid use with nitrates. A minimum of 24 hours must pass before administration of nitrates in situations deemed medically necessary.
References
- ↑ 1.00 1.01 1.02 1.03 1.04 1.05 1.06 1.07 1.08 1.09 1.10 1.11 1.12 1.13 1.14 1.15 1.16 1.17 1.18 1.19 Viagra® [Package Insert]. New York, NY: Pfizer Pharmaceuticals, 2006.
- ↑ 2.0 2.1 2.2 2.3 2.4 Revatio™ [Package Insert]. New York, NY: Pfizer Pharmaceuticals, 2006.
- ↑ Shabsigh R. Seftel AD. Rosen RC. Porst H. Ahuja S. Deeley MC. Garcia CS. Giuliano F. Review of time of onset and duration of clinical efficacy of phosphodiesterase type 5 inhibitors in treatment of erectile dysfunction. Urology. 68(4):689-96, 2006 Oct.]
- ↑ Setter SM. Iltz JL. Fincham JE. Campbell RK. Baker DE. Phosphodiesterase 5 inhibitors for erectile dysfunction. Annals of Pharmacotherapy. 39(7-8):1286-95, 2005 Jul-Aug.]
- ↑ Padma-Nathan H, Steers WD, Wicker PA, Padma-Nathan H, Steers WD, Wicker PA. Efficacy and safety of oral sildenafil in the treatment of erectile dysfunction: a double-blind, placebo-controlled study of 329 patients. Sildenafil Study Group. Int J Clin Pract. 1998 Sep;52(6):375-9.
- ↑ Goldstein I, Lue TF, Padma-Nathan H, Rosen RC, Steers WD, Wicker PA, et al. Oral sildenafil in the treatment of erectile dysfunction. Sildenafil Study Group.[see comment][erratum appears in N Engl J Med 1998 Jul 2;339(1):59]. N Engl J Med. 1998 May 14;338(20):1397-404.
- ↑ Lewis R, Bennett CJ, Borkon WD, Boykin WH, Althof SE, Stecher VJ, et al. Patient and partner satisfaction with Viagra (sildenafil citrate) treatment as determined by the Erectile Dysfunction Inventory of Treatment Satisfaction Questionnaire. Urology. 2001 May;57(5):960-5.
- ↑ Singh, T.P., et al., A randomized, placebo-controlled, double-blind, crossover study to evaluate the efficacy of oral sildenafil therapy in severe pulmonary artery hypertension. American Heart Journal, 2006. 151(4): p. 851.e1-5.
- ↑ Galie, N., et al., Sildenafil citrate therapy for pulmonary arterial hypertension. New England Journal of Medicine, 2005. 353(20): p. 2148-57.
- ↑ Sastry, B.K., et al., Clinical efficacy of sildenafil in primary pulmonary hypertension: a randomized, placebo-controlled, double-blind, crossover study. Journal of the American College of Cardiology, 2004. 43(7): p. 1149-53.
- ↑ Michelakis E, Tymchak W, Lien D, Webster L, Hashimoto K, Archer S, et al. Oral sildenafil is an effective and specific pulmonary vasodilator in patients with pulmonary arterial hypertension: comparison with inhaled nitric oxide. Circulation. 2002 May 21;105(20):2398-403.
- ↑ Ghofrani HA, Wiedemann R, Rose F, Schermuly RT, Olschewski H, Weissmann N, et al. Sildenafil for treatment of lung fibrosis and pulmonary hypertension: a randomised controlled trial. Lancet. 2002 Sep 21;360(9337):895-900.
- ↑ Fries R. Shariat K. von Wilmowsky H. Bohm M. Sildenafil in the treatment of Raynaud's phenomenon resistant to vasodilatory therapy. Circulation. 112(19):2980-5, 2005 Nov 8.
- ↑ Salerian AJ. Deibler WE. Vittone BJ. Geyer SP. Drell L. Mirmirani N. Mirczak JA. Byrd W. Tunick SB. Wax M. Fleisher S. Sildenafil for psychotropic-induced sexual dysfunction in 31 women and 61 men. Journal of Sex & Marital Therapy. 26(2):133-40, 2000 Apr-Jun.
- ↑ Nurnberg HG. Hensley PL. Gelenberg AJ. Fava M. Lauriello J. Paine S. Treatment of antidepressant-associated sexual dysfunction with sildenafil: a randomized controlled trial. JAMA. 289(1):56-64, 2003 Jan 1.
- ↑ Nurnberg HG. Hensley PL. Lauriello J. Parker LM. Keith SJ. Sildenafil for women patients with antidepressant-induced sexual dysfunction. Psychiatric Services. 50(8):1076-8, 1999 Aug.
- ↑ Webb DJ. Freestone S. Allen MJ. Muirhead GJ. Sildenafil citrate and blood-pressure-lowering drugs: results of drug interaction studies with an organic nitrate and a calcium antagonist. American Journal of Cardiology. 83(5A):21C-28C, 1999 Mar 4.
- ↑ Muirhead GJ. Wulff MB. Fielding A. Kleinermans D. Buss N. Pharmacokinetic interactions between sildenafil and saquinavir/ritonavir. British Journal of Clinical Pharmacology. 50(2):99-107, 2000 Aug.
- ↑ Merry C. Barry MG. Ryan M. Tjia JF. Hennessy M. Eagling VA. Mulcahy F. Back DJ. Interaction of sildenafil and indinavir when co-administered to HIV-positive patients. AIDS. 13(15):F101-7, 1999 Oct 22.
- ↑ Auerbach SM. Gittelman M. Mazzu A. Cihon F. Sundaresan P. White WB. Simultaneous administration of vardenafil and tamsulosin does not induce clinically significant hypotension in patients with benign prostatic hyperplasia. Urology. 64(5):998-1003; discussion 1003-4, 2004 Nov.
- ↑ Kloner RA. Jackson G. Emmick JT. Mitchell MI. Bedding A. Warner MR. Pereira A. Interaction between the phosphodiesterase 5 inhibitor, tadalafil and 2 alpha-blockers, doxazosin and tamsulosin in healthy normotensive men. Journal of Urology. 172(5 Pt 1):1935-40, 2004 Nov.
- ↑ Galatti L. Fioravanti A. Salvo F. Polimeni G. Giustini SE. Interaction between tadalafil and itraconazole. Annals of Pharmacotherapy. 39(1):200, 2005 Jan.
- ↑ Wilner K. Laboy L. LeBel M. The effects of cimetidine and antacid on the pharmacokinetic profile of sildenafil citrate in healthy male volunteers. British Journal of Clinical Pharmacology. 53 Suppl 1:31S-36S, 2002.
- ↑ Hesse C. Siedler H. Burhenne J. Riedel KD. Haefeli WE. Fluvoxamine affects sildenafil kinetics and dynamics. Journal of Clinical Psychopharmacology. 25(6):589-92, 2005 Dec.
- ↑ Paul GA. Gibbs JS. Boobis AR. Abbas A. Wilkins MR. Bosentan decreases the plasma concentration of sildenafil when coprescribed in pulmonary hypertension. British Journal of Clinical Pharmacology. 60(1):107-12, 2005 Jul.
PUBMED References
Efficacy Trial Articles
- O'Leary MP. Althof SE. Cappelleri JC. Crowley A. Sherman N. Duttagupta S. The United States Self-Esteem and Relationship Questionnaire Study Group. Self-esteem, confidence and relationship satisfaction of men with erectile dysfunction treated with sildenafil citrate: a multicenter, randomized, parallel group, double-blind, placebo controlled study in the United States. Journal of Urology. 175:1058-62, 2006 Mar.
- Singh, T.P., et al., A randomized, placebo-controlled, double-blind, crossover study to evaluate the efficacy of oral sildenafil therapy in severe pulmonary artery hypertension. American Heart Journal, 2006. 151(4): p. 851.e1-5.
- Michelakis E, Tymchak W, Lien D, Webster L, Hashimoto K, Archer S, et al. Oral sildenafil is an effective and specific pulmonary vasodilator in patients with pulmonary arterial hypertension: comparison with inhaled nitric oxide. Circulation. 2002 May 21;105(20):2398-403.
- Ghofrani HA, Wiedemann R, Rose F, Schermuly RT, Olschewski H, Weissmann N, et al. Sildenafil for treatment of lung fibrosis and pulmonary hypertension: a randomised controlled trial. Lancet. 2002 Sep 21;360(9337):895-900.
- Fries R. Shariat K. von Wilmowsky H. Bohm M. Sildenafil in the treatment of Raynaud's phenomenon resistant to vasodilatory therapy. Circulation. 112(19):2980-5, 2005 Nov 8.
Therapeutic Class Comparison Trial Articles
- Tolra JR. Campana JM. Ciutat LF. Miranda EF. Prospective, randomized, open-label, fixed-dose, crossover study to establish preference of patients with erectile dysfunction after taking the three PDE-5 inhibitors. Journal of Sexual Medicine. 3(5):901-9, 2006 Sep.
- Rubio-Aurioles E. Porst H. Eardley I. Goldstein I. Vardenafil-Sildenafil Comparator Study Group. Comparing vardenafil and sildenafil in the treatment of men with erectile dysfunction and risk factors for cardiovascular disease: a randomized, double-blind, pooled crossover study. Journal of Sexual Medicine. 3(6):1037-49, 2006 Nov.
- Govier F. Potempa AJ. Kaufman J. Denne J. Kovalenko P. Ahuja S. A multicenter, randomized, double-blind, crossover study of patient preference for tadalafil 20 mg or sildenafil citrate 50 mg during initiation of treatment for erectile dysfunction. Clinical Therapeutics. 25(11):2709-23, 2003 Nov.
Pharmacokinetics Articles
- Boolell M. Allen MJ. Ballard SA. Gepi-Attee S. Muirhead GJ. Naylor AM. Osterloh IH. Gingell C. Sildenafil: an orally active type 5 cyclic GMP-specific phosphodiesterase inhibitor for the treatment of penile erectile dysfunction. International Journal of Impotence Research. 8(2):47-52, 1996 Jun.
- Warrington JS. Shader RI. von Moltke LL. Greenblatt DJ. In vitro biotransformation of sildenafil (Viagra): identification of human cytochromes and potential drug interactions. Metabolism & Disposition. 28(4):392-7, 2000 Apr.
- Walker DK. Ackland MJ. James GC. Muirhead GJ. Rance DJ. Wastall P. Wright PA. Pharmacokinetics and metabolism of sildenafil in mouse, rat, rabbit, dog and man. Xenobiotica. 29(3):297-310, 1999 Mar.
- Nichols DJ. Muirhead GJ. Harness JA. Pharmacokinetics of sildenafil after single oral doses in healthy male subjects: absolute bioavailability, food effects and dose proportionality. British Journal of Clinical Pharmacology. 53 Suppl 1:5S-12S, 2002.
Drug Interaction Articles
- Paul GA. Gibbs JS. Boobis AR. Abbas A. Wilkins MR. Bosentan decreases the plasma concentration of sildenafil when coprescribed in pulmonary hypertension. British Journal of Clinical Pharmacology. 60(1):107-12, 2005 Jul.
- Hesse C. Siedler H. Burhenne J. Riedel KD. Haefeli WE. Fluvoxamine affects sildenafil kinetics and dynamics. Journal of Clinical Psychopharmacology. 25(6):589-92, 2005 Dec.
- Wilner K. Laboy L. LeBel M. The effects of cimetidine and antacid on the pharmacokinetic profile of sildenafil citrate in healthy male volunteers. British Journal of Clinical Pharmacology. 53 Suppl 1:31S-36S, 2002.
- Muirhead GJ. Wulff MB. Fielding A. Kleinermans D. Buss N. Pharmacokinetic interactions between sildenafil and saquinavir/ritonavir. British Journal of Clinical Pharmacology. 50(2):99-107, 2000 Aug.
- Merry C. Barry MG. Ryan M. Tjia JF. Hennessy M. Eagling VA. Mulcahy F. Back DJ. Interaction of sildenafil and indinavir when co-administered to HIV-positive patients. AIDS. 13(15):F101-7, 1999 Oct 22.
- Webb DJ. Freestone S. Allen MJ. Muirhead GJ. Sildenafil citrate and blood-pressure-lowering drugs: results of drug interaction studies with an organic nitrate and a calcium antagonist. American Journal of Cardiology. 83(5A):21C-28C, 1999 Mar 4.
Images
External Links
- Manufacturers/Distributors
Pfizer Pharmaceuticals; Pfizer
- Patient information pages
- Healthcare professional information pages
Viagra Healthcare Professional Information; Viagra Package Insert
