Sildenafil (Systemic)


VA CLASSIFICATION
Primary: GU900

Note: For a listing of dosage forms and brand names by country availability, see Dosage Forms section(s).



Category:


Impotence therapy agent (systemic)—

Indications

General considerations
Erectile dysfunction that is medication-induced or caused by endocrine problems, such as hypogonadism or hypothyroidism or hyperthyroidism, should be evaluated and appropriately treated before sildenafil treatment is considered {05}.

Cardiac risk associated with sexual activity should be individually assessed prior to initiating any treatment for erectile dysfunction {04}{05}.

Accepted

Erectile dysfunction (treatment)—Sildenafil is indicated to facilitate erections in men with erectile dysfunction {04}{05}.
—Sildenafil has been evaluated in 3000 patients (19 to 87 years of age) in 21 studies of up to 6 months. Compared with patients taking a placebo, patients taking sildenafil demonstrated statistically significant improvement in treatment of erectile dysfunction of organic, psychogenic, or mixed etiologies (mean onset of 5 years). Sildenafil was effective in a broad range of patients, including those with a history of coronary artery disease, hypertension, other cardiac disease, peripheral vascular disease, diabetes mellitus, depression, coronary artery bypass graft (CABG), radical prostatectomy, transurethral resection of the prostate (TURP), and spinal cord injury. Sildenafil was also effective in patients taking antidepressant, antipsychotic, antihypertensive, or diuretic medications. {04} {05}


Pharmacology/Pharmacokinetics

Note: The pharmacokinetics of sildenafil are dose-proportional over the recommended dosage range{05} (25 mg to 100 mg){04}.


Physicochemical characteristics:
Molecular weight—
    666.7 {02}{04}{05}

Mechanism of action/Effect:

Impotence therapy agent—Sildenafil is a selective inhibitor of phosphodiesterase type 5 (PDE5), an enzyme responsible for degrading cyclic guanosine monophosphate (cGMP) in the corpus cavernosum. By diminishing the effect of PDE5, sildenafil facilitates the effect of nitric oxide during sexual stimulation: cGMP levels increase, smooth muscle relaxes, and blood flows into the corpus cavernosum, producing an erection. Without sexual stimulation, sildenafil has no effect on erections. {04}{05}

In vitro studies show that sildenafil's potency for action on phosphodiesterases differs. Sildenafil's action is greater for PDE5 than for the following phosphodiesterases: PDE1 (> 80 times); PDE2 and PDE4 (> 1000 times); PDE3 (about 4000 times), and PDE6 (about 10 times). PDE3 controls cardiac contractility and PDE6, an enzyme found in the retina, may be involved in color vision abnormalities reported for the higher dose of sildenafil. The active metabolite of sildenafil has approximately 50% potency for PDE5, and contributes approximately 20% of sildenafil's effect. {04}{05}

Absorption:

Rapidly absorbed; absolute bioavailability is approximately 40%. A high-fat meal reduces absorption as shown by reducing the maximum plasma concentration (C max) by 29% and delaying time to peak concentration (T max) by 60 minutes. {04}{05}

Distribution:

The mean steady state volume of distribution (Vol ss) is 105 liters. Less than 0.001% of sildenafil remained in the semen of healthy volunteers at 90 minutes. {04}{05}

Protein binding:

Very high (96% bound to plasma proteins); independent of total plasma concentration {04}{05}{06}.

Biotransformation:

Hepatic metabolism, via cytochrome P450 (CYP) 3A4 (major route) and CYP2C9 (minor route). Sildenafil is converted by N-desmethylation to an active metabolite with properties similar to those of the parent, sildenafil. Parent and active metabolite are metabolized further. {04}{05}

Half-life:

4 hours (terminal half-life for parent and major metabolite) {04}{05}.

Onset of action:

Within 0.5 hour after administration {01}{04}.

Time to peak concentration:

30 to 120 minutes under fasting conditions; attainment of peak concentration level is delayed by 60 minutes when given with a high-fat meal {04}{05}.

Peak serum concentration:

Sildenafil—Approximately 440 nanograms per mL {03}; major metabolite has 40% of the serum concentration of sildenafil {04}{05}.

Duration of action:

Up to 4 hours, but with less response than that seen at 2 hours {05}.

Elimination:
    Feces (80% of the administered dose as metabolites); urine (13% of the administered dose as metabolites) {04}{05}.


Precautions to Consider

Carcinogenicity

In 24-month animal studies, sildenafil was not found to be carcinogenic in male rats given 29 times the maximum recommended human dose (MRHD) or in female rats given 42 times the MRHD. In 18- to 21-month studies, sildenafil was not carcinogenic in mice given 10 mg per kg of body weight (mg/kg) a day, corresponding to 0.6 times the MRHD (based on a mg per square meter of body surface area). {04}{05}

Mutagenicity

Sildenafil was not found to be mutagenic in an in vivo mouse micronucleus assay or an in vitro human lymphocytes assay and bacterial or Chinese hamster ovary cell assays {04}{05}.

Pregnancy/Reproduction
Fertility—
Single doses of 100 mg sildenafil given to males did not impair sperm motility or morphology {05}.

In animal studies, sildenafil did not impair fertility in rats given sildenafil in doses of 60 mg/kg a day for 36 days in females and for 102 days in males, corresponding to an area under the plasma concentration–time curve (AUC) that was greater than 25 times that produced in humans {05}.

Pregnancy—
Adequate and well-controlled studies in humans have not been done. Sildenafil is not indicated for use in females {04}{05}.

In animal studies, sildenafil was not teratogenic, embryotoxic, or fetotoxic in rats and rabbits given up to 200 mg/kg a day during organogenesis, corresponding to 20 to 40 times the MRHD as calculated per body surface area of a 50-kg person {04}{05}.

FDA Pregnancy Category B {05}.

Breast-feeding

Problems in humans have not been documented; sildenafil is not indicated for use in females {04}{05}.

Geriatrics


Healthy volunteers 65 years of age and over cleared sildenafil less effectively from the plasma than did healthy younger volunteers 18 to 45 years of age as shown by a 40% increase of AUC in older adults. Using an initial lower dose of 25 mg is recommended for patients 65 years of age and over. {04}{05}

Drug interactions and/or related problems
The following drug interactions and/or related problems have been selected on the basis of their potential clinical significance (possible mechanism in parentheses where appropriate)—not necessarily inclusive (» = major clinical significance):


Note: Combinations containing any of the following medications, depending on the amount present, may also interact with this medication.
The safety and efficacy of combining sildenafil treatment with other impotence therapy agents have not been studied {05}.

Antihypertensive medications    (concurrent use may potentiate the hypotensive effect of these medications; a mean additional reduction in supine blood pressure, 8 mm Hg systolic and 7 mm Hg diastolic, was observed in a study when sildenafil was given concurrently with amlodipine in either 5-mg or 10-mg strengths {05})


» Enzyme inhibitors, hepatic, cytochrome P450 (CYP) 3A4 including:
Cimetidine
Erythromycin
Itraconazole
Ketoconazole
Mibefradil
Ritonavir
Saquinavir    (an increase in sildenafil plasma concentrations is likely to occur with CYP3A4 inhibitors because they reduce the metabolism and clearance of sildenafil; using a lower dose of 25 mg is recommended for patients taking these medications. For patients taking ritonavir, a maximum single dose not to exceed 25 mg every 48 hours is recommended. Plasma concentrations of sildenafil increased 56% when a 50-mg dose of sildenafil was administered with cimetidine 800 mg; AUC of sildenafil increased 182% when a single 100-mg dose of sildenafil was administered after steady-state concentrations of erythromycin were achieved at 5 days; similar reactions are expected with stronger CYP3A4 inhibitors, such as ketoconazole, itraconazole, and mibefradil; coadministration of saquinavir (1200 mg 3 times a day at steady state) and sildenafil 100 mg, or ritonavir (500 mg twice a day at steady state) and sildenafil 100 mg resulted in a 140% and 300% increase in sildenafil Cmax and a 210% and 1000% increase in sildenafil AUC, respectively{04}{05} )


Enzyme inducers, hepatic, cytochrome P450 (CYP) 3A4, including rifampin    (a decrease in sildenafil plasma concentrations is likely to occur with CYP3A4 inducers because they increase the metabolism and clearance of sildenafil {04}{05})


» Nitrates, including nitroglycerin    (sildenafil potentiates the hypotensive effect of nitrates; concomitant use is contraindicated {04}{05})


Note: It has not been determined when patients may safely receive nitrates, if they are considered necessary, after having taken sildenafil. {04}{05} Although plasma concentrations of sildenafil (100 mg) at 24 hours postdose (approximately 2 nanograms per mL) are much lower than at peak concentration (approximately 440 nanograms per mL), it is not known if nitrates may be administered safely at that point. {04}{05} Also, these plasma concentration data are taken from healthy volunteers. {04}{05} Hepatic or renal impairment, concurrent administration of a CYP 3A4 inhibitor, or an age > 65 years may result in an increase in the plasma concentration of sildenafil to three to eight times that seen in healthy volunteers. {04}{05}


Medical considerations/Contraindications
The medical considerations/contraindications included have been selected on the basis of their potential clinical significance (reasons given in parentheses where appropriate)— not necessarily inclusive (» = major clinical significance).


Risk-benefit should be considered when the following medical problems exist
Abnormalities of the penis, such as:
Anatomical deformity
Angulation of the penis
Cavernosal fibrosis
Hypospadia, severe
Peyronie's disease    (patients who have an anatomical deformity, angulation of the penis, cavernosal fibrosis, or Peyronie's disease are at increased risk of developing problems when using impotence therapy agents, including sildenafil {04}{05})


Bleeding disorders, including peptic ulcer, active or
Coagulation defects, severe    (risk of bleeding may be increased since sildenafil may inhibit platelet aggregation as shown in in vitro studies; further study is needed. Safety information is not available for use of sildenafil in these patients {04}{05})


Cardiac failure
(patients with stable cardiac disease experienced a mean decrease of 7% in cardiac output after receiving a total dose of sildenafil 40 mg intravenously over 4 infusions{03}{06}
Coronary artery disease causing unstable angina or
Hypertension resulting in a blood pressure > 170/100 mm Hg or
Hypotension resulting in a blood pressure < 90/50 mm Hg or
Life-threatening arrhythmia, history of (within the previous 6 months) or
Myocardial infarction, history of (within the previous 6 months) or
Stroke, history of (within the previous 6 months)     (it is recommended that sildenafil be prescribed with caution in these patients since controlled clinical data regarding safety and efficacy are not yet available ; also, cardiac risk associated with sexual activity should be assessed individually prior to initiation of any treatment for erectile dysfunction {04}{05})

    (consideration as to whether these patients could be adversely affected by the vasodilatory effects of sildenafil, such as the transient decreases in supine blood pressure [mean maximum decrease 8.4/5.5 mm Hg], is recommended {04}{05})


Cardiovascular disease, other    (serious, life-threatening cardiovascular events with a temporal relationship to dosing with sildenafil have been described in post-marketing reports; these have included myocardial infarction, hypertension, ventricular arrhythmia, cerebrovascular hemorrhage, sudden cardiac death, and transient ischemic attacks{06}. Cardiac risk associated with sexual activity should be assessed individually prior to initiation of any treatment for erectile dysfunction; consideration as to whether these patients could be adversely affected by the vasodilatory effects of sildenafil, such as the transient decreases in supine blood pressure [mean maximum decrease 8.4/5.5 mmHg], is recommended{04}{05})


» Cirrhosis or
» Hepatic function impairment, severe    (sildenafil clearance was reduced in volunteers with hepatic cirrhosis [Child-Pugh A and B], resulting in an increase of AUC by 84% and of C max by 47% when compared with data of age-matched volunteers who had no hepatic impairment; using a lower initial dose of 25 mg of sildenafil is recommended for these patients {04}{05})


Leukemia or
Myeloma, multiple or
Polycythemia or
Priapism, history of or
Sickle cell disease or
Thrombocythemia    (patients with these predisposing conditions have an increased risk of priapism {05})


» Renal function impairment, severe    (creatinine clearance of less than 30 mL/min [severe renal insufficiency] significantly reduced sildenafil clearance, approximately doubling AUC and C max compared with those of age-matched volunteers who had no renal impairment; using a lower initial dose of 25 mg of sildenafil is recommended for these patients. Creatinine clearance of 30 to 80 mL/min [mild to moderate renal insufficiency] did not alter pharmacokinetics of 50 mg sildenafil as a single dose {04}{05})


Retinitis pigmentosa    (a minority of patients with this condition also experience genetic disorders of retinal phosphodiesterases; due to a lack of data on safety and efficacy, it is recommended that sildenafil be prescribed with caution in these patients {04}{05}{06})


Sensitivity to sildenafil {04}{05}


Side/Adverse Effects

Note: Serious cardiovascular events, including myocardial infarction, sudden cardiac death, ventricular arrhythmia, cerebrovascular hemorrhage, transient ischemic attack (TIA), and hypertension, have occurred with use of sildenafil; these effects had not been reported prior to its approval by the Food and Drug Administration (FDA). Most, but not all, of the patients who experienced these events had pre-existing cardiovascular risk factors. Many of these events occurred during or shortly following sexual activity; however, a few occurred shortly after the use of sildenafil in the absence of sexual activity. It is unknown at present whether these events are related directly to sildenafil, to sexual activity, to underlying cardiovascular disease, to a combination of these factors, or to other factors. {03}{04}{05} See also the Medical considerations/Contraindications section.
Sildenafil produces a transient decrease in blood pressure through vasodilation. Single oral doses of 100 mg of sildenafil have produced a decrease in the supine blood pressure (mean maximum decrease of 8.4/5.5 mm Hg). This hypotensive effect was most prominent at 1 to 2 hours after the dose was administered. Since similar results were observed with the 25-mg and 50-mg doses of sildenafil, this effect does not appear to be related to either the dose or plasma concentration. {04}{05}

The following side/adverse effects have been selected on the basis of their potential clinical significance (possible signs and symptoms in parentheses where appropriate)—not necessarily inclusive:

Those indicating need for medical attention
Incidence less frequent
—2 to 3%    
Abnormal vision, including blurred vision
color change perception ( seeing shades of colors differently than before), or sensitivity to light {04}{05}— may be mild and transient
    
dizziness
{04}{05}    
urinary tract infection or cystitis ( bladder pain; cloudy or bloody urine ; increased frequency of urination; pain on urination){04}{05}

Note: In fixed-dose studies, abnormal vision was more common at the 100-mg dose (incidence of 11%) than at lower doses {05}.


Incidence rare
    
Hematuria {04}{05} (blood in urine )
    
ophthalmic effects, such as diplopia {04}{05} (double vision ), increased intraocular pressure {04}{05}
paramacular edema {04}{05} (blurred vision or other changes in vision), redness, burning or swelling of the eye {04}{05}
retinal vascular disease or bleeding {04}{05} (changes in vision; bleeding of eye), vision loss, temporary {04}{05}
or vitreous detachment or traction {04}{05} (decrease in vision or other changes in vision )
    
prolonged erection {04}{05}
    
priapism {04}{05} (prolonged, painful, inappropriate erection of penis)
    
seizures {04}{05}

Note: The following side/adverse effects reported in clinical trials or following the approval of sildenafil have not been established as being caused by sildenafil {04}{05}.

    
Allergic reaction ( skin rash; hives; itching of skin){04}{05}
    
anemia or asthenia (unusual tiredness or weakness){04}{05}
    
arthrosis
arthritis
gout or hyperuricemia {04}{05}
synovitis or tenosynovitis
tendon rupture (bone pain; lower back or side pain; painful, swollen joints){04}{05}
    
breast enlargement {04}{05}
    
cardiovascular effects , such as angina pectoris (chest pain), AV block (fainting; trouble in breathing; unusual weakness), cardiac arrest or sudden cardiac death {03} (heart failure), cerebral thrombosis (confusion; numbness of hands), cerebrovascular hemorrhage {03} (headache, severe or continuing; seizures; sudden weakness; vision changes, such as blurred vision or temporary blindness), hypertension (dizziness, severe; headache, continuing), hypotension {01} , including orthostatic hypotension (dizziness or lightheadedness, especially when getting up from a lying or sitting position; low blood pressure), migraine headache
myocardial ischemia, myocardial infarction or transient ischemic attack {03} ( chest pain; fainting; fast heartbeat; increased sweating; nausea, continuing or severe ; nervousness; shortness of breath; weakness), palpitation (pounding heartbeat), syncope (fainting), tachycardia (fast heartbeat), and ventricular arrhythmia (irregular heartbeat){04}{05}
    
chills {01}{04}
    
deafness {01}{04}
    
edema (swelling of face, hands, feet, or lower legs){01}{04}
    
hyperglycemia (faintness ; nausea; paleness of skin; sweating), or hypoglycemia reaction ( anxiety; behavior change similar to drunkenness ; blurred vision; cold sweats; confusion; cool, pale skin; difficulty in concentrating; drowsiness ; excessive hunger; fast heartbeat; headache; nausea; nervousness; nightmares; restless sleep; shakiness; slurred speech; unusual tiredness or weakness)—especially for patients with diabetes mellitus {01}{04}
    
hypernatremia (confusion ; convulsions; decrease in amount of urine or in frequency of urination; dizziness; fast heartbeat; headache; increased thirst; swelling of feet or lower legs; twitching of muscles; unusual tiredness or weakness){01}{04}
    
leukopenia (sore throat and fever or chills){01}{04}
    
myasthenia (weakness of muscles){01}{04}
    
ophthalmic effects {01} , such as cataracts
conjunctivitis (feeling of something in the eye; redness, itching, or tearing of eyes), dry eyes
eye hemorrhage (eye pain), and mydriasis (increase in size of pupil){01}{04}
    
shock (fainting){01}{04}
    
skin effects {01} , such as contact dermatitis
pruritus
or urticaria ( hives; itching; redness of skin), exfoliative dermatitis ( dryness, redness, scaling, or peeling of the skin), herpes simplex (groups of skin lesions with swelling; unusual feeling of burning or stinging of skin ), and skin ulcers {01}{04}




Those indicating need for medical attention only if they continue or are bothersome
Incidence more frequent
    
Dyspepsia (stomach discomfort following meals)—7%{01}{04}
    
flushing —10%{01}{04}
    
headache —16%{01}{04}
    
nasal congestion —4%{01}{04}

Note:  In fixed-dose studies, dyspepsia was more common at the 100-mg dose (incidence of 17%) than at lower doses {01}{05}.


Incidence less frequent
    
Diarrhea {01}{04}

Incidence rare
    
Anxiety

Note: The following side/adverse effects reported in clinical trials of sildenafil have not been established as being caused by sildenafil {01}{04}.

    
Abdominal pain {01}{04}
    
central nervous system (CNS) symptoms {01} , such as abnormal dreams
ataxia (clumsiness or unsteadiness ), decreased reflexes (lack of coordination), hypertonia ( tense muscles), hypesthesia (increased skin sensitivity ), insomnia (trouble in sleeping), mental depression
neuralgia
neuropathy
paresthesia
or tremor (aches, pains, or weakness of muscles; numbness or tingling of hands, legs, or feet; trembling and shaking; unusual feeling of burning or stinging of skin ), somnolence (sleepiness), and vertigo (sensation of motion, usually whirling, either of one's self or of one's surroundings){01}{04}
    
ear pain {01}{04}
    
gastrointestinal effects {01} , such as colitis (severe diarrhea or stomach cramps), dry mouth, esophagitis, gastritis, and stomatitis (difficulty in swallowing; redness or irritation of the tongue; sores in mouth and on lips), gastroenteritis (abdominal pain; diarrhea, severe; nausea), gingivitis (redness, soreness, swelling, or bleeding of gums), rectal bleeding
and vomiting {01}{04}
    
increased amount of saliva {01}{04}
    
increased sweating or thirst {01}{04}
    
myalgia (aches or pains in muscles){01}{04}
    
respiratory effects {01} , such as asthma
bronchitis
dyspnea
laryngitis
pharyngitis
and sinusitis (cough; shortness of breath or troubled breathing ; tightness of chest or wheezing){01}{04}
    
tinnitus (ringing or buzzing in ears){01}{04}
    
urogenital effects {01} , such as abnormal ejaculation or anorgasmia ( failure to experience a sexual orgasm; sexual problems in men, continuing), nocturia (waking to urinate at night ), urinary frequency, and urinary incontinence (loss of bladder control){01}{04}






Overdose
For more information on the management of overdose or unintentional ingestion, contact a poison control center (see Poison Control Center Listing ).

Clinical effects of overdose
In studies with healthy volunteers taking single doses of up to 800 mg, adverse events were similar to those seen at lower doses but incidence rates were increased {04}{05}.

Treatment of overdose
To enhance elimination—Renal dialysis is not expected to accelerate clearance of sildenafil; sildenafil is highly bound to plasma proteins and is not eliminated in the urine {04}{05}.

Supportive care—Supportive treatment should be adopted as required {04}{05}. Patients in whom intentional overdose is confirmed or suspected should be referred for psychiatric consultation.


Patient Consultation
As an aid to patient consultation, refer to Advice for the Patient, Sildenafil (Systemic) .
In providing consultation, consider emphasizing the following selected information (» = major clinical significance):

Before using this medication
»   Conditions affecting use, especially:
Sensitivity to sildenafil





Use in the elderly—Patients 65 years of age and older should be started at 25 mg of sildenafil because of their slower metabolism and clearance and should be monitored more often for side/adverse effects
Other medications, especially enzyme inhibitors, hepatic, cytochrome P450 3A4, including cimetidine, erythromycin, itraconazole, ketoconazole, mibefradil, ritonavir, and saquinavir; or nitrates, including nitroglycerin
Other medical problems, especially cirrhosis or severe hepatic or renal function impairment

Proper use of this medication
» Reading patient package insert

Knowing that medication begins to work within 30 minutes after taking it and effect continues for up to 4 hours, lessening after 2 hours

» Proper dosing

» Proper storage

Precautions while using this medication
» Concurrent use of other impotence therapy agents is not presently recommended

» Complying with therapy dose recommendations; importance of not exceeding prescribed dosage and frequency of use

» Checking with physician immediately if a prolonged erection, 4 or more hours in duration, occurs


Side/adverse effects
Signs of potential side effects, especially abnormal vision, including blurred vision, color change perception, and sensitivity to light; dizziness; urinary tract infection or cystitis; hematuria; ophthalmic effects, such as diplopia, increased intraocular pressure, paramacular edema, redness, burning, or swelling of the eye, retinal vascular disease or bleeding, temporary vision loss, or vitreous detachment or traction; prolonged erection; priapism; seizures

Signs of potential side effects (although not proven to be caused by sildenafil, but reported in clinical trials or in postmarketing experience), especially allergic reaction; anemia or asthenia; arthrosis, arthritis, gout or hyperuricemia, synovitis (including tenosynovitis), tendon rupture; breast enlargement; cardiovascular effects, such as angina pectoris, AV block, cardiac arrest or sudden cardiac death, cerebral thrombosis, cerebrovascular hemorrhage, hypertension, hypotension (including orthostatic hypotension), migraine headache, myocardial ischemia, myocardial infarction or transient ischemic attack palpitation, syncope, tachycardia, and ventricular arrhythmia; chills; deafness; edema; hyperglycemia or hypoglycemia—especially for patients with diabetes mellitus; hypernatremia; leukopenia; myasthenia; ophthalmic effects, such as cataracts, conjunctivitis, dry eyes, eye hemorrhage, mydriasis; shock; or skin effects, such as contact dermatitis, pruritus, urticaria, exfoliative dermatitis, herpes simplex, and skin ulcer


General Dosing Information
For treatment of untreated erectile dysfunction—Sildenafil improved frequency, firmness, and maintenance of erections; frequency of orgasm; frequency and level of desire; frequency, satisfaction, and enjoyment of intercourse; and overall relationship satisfaction {05}.

For treatment of erectile dysfunction due to a radical prostatectomy–Across all trials, sildenafil improved the erections of 43% of patients compared with improvement in 15% of the patients taking a placebo {05}.

For treatment of erectile dysfunction due to complications of diabetes mellitus—Sildenafil improved frequency of successful penetration during sexual activity and maintenance of erections after penetration, compared to patients taking a placebo. Fifty-seven percent of patients taking sildenafil reported improved erections compared with 10% of patients taking a placebo. {05}

For treatment of erectile dysfunction due to a spinal cord injury—Sildenafil improved frequency of successful penetration during sexual activity and maintenance of erections after penetration. Eighty-three percent of patients taking sildenafil reported improved erections compared with 12% of patients taking a placebo. {05}

For treatment of erectile dysfunction due to psychogenic etiology—Sildenafil improved frequency of successful penetration during sexual activity and maintenance of erections after penetration. Eighty-four percent of patients taking sildenafil reported improved erections compared with 26% of patients taking a placebo. {05}

Treatment of prolonged erection or priapism
A prolonged erection should be treated if it persists longer than 4 hours; priapism should be treated immediately. If priapism is not treated promptly, penile tissue damage and/or permanent loss of potency may result. Procedures for detumescence are listed below:{04}
   • Aspirate 40 to 60 mL of blood from either left or right corpora using vacutainer and holder for drawing blood. Apply ice for 20 minutes post aspiration if erection remains.{04}
   • If the above procedure is unsuccessful, put patient in supine position. Dilute phenylephrine 10 mg into 20 mL sterile water for injection. Using an insulin syringe, inject 0.1 to 0.2 mL (50 to 100 mcg) into the corpora every 2 to 5 minutes until detumescence occurs.Patients may develop transient bradycardia and hypertension due to phenylephrine injections. Monitor patient's blood pressure and pulse every 10 minutes. Patients with cardia arrhythmia and diabetes may be at higher risk. Do not give phenylephrine to patients on MAO inhibitors. Phenylephrine is usually effective in the majority of patients if used within 12 hours of erection.{04}
   • If the above measures fail to detumesce the patient, consult a urologist as soon as possible.{04}


Oral Dosage Forms

SILDENAFIL CITRATE TABLETS

Usual adult dose
Erectile dysfunction
Oral, 50 mg (base) one hour (range, one half to four hours) before sexual intercourse once a day if needed. As tolerated, subsequent doses may be increased to 100 mg or decreased to 25 mg once a day. {04}{05}


Usual adult prescribing limits
100 mg once a day {04}{05}{06}.

Usual geriatric dose
Erectile dysfunction
Oral, 25 mg (base) one hour (range, one half to four hours) before sexual intercourse once a day if needed. As tolerated, subsequent doses may be increased. {04}{05}


Strength(s) usually available
U.S.—


25 mg (base) (Rx) [Viagra (film-coated ) (croscarmellose sodium) ( lactose) (magnesium stearate){01}]


50 mg (base) (Rx) [Viagra ( film-coated) (croscarmellose sodium) (lactose) (magnesium stearate){01}]


100 mg (base) (Rx) [Viagra (film-coated ) (croscarmellose sodium) ( lactose) (magnesium stearate){01}]

Canada—


25 mg (base) (Rx) [Viagra (FD&C Blue #2 aluminium lake) ( lactose)]


50 mg (base) (Rx) [Viagra (FD&C Blue #2 aluminium lake) ( lactose)]


100 mg (base) (Rx) [Viagra (FD&C Blue #2 aluminium lake) ( lactose)]

Packaging and storage:
Store below 40 °C (104 °F), preferably between 15 and 30 °C (59 and 86 °F) {04}{05}.

Note: Include patient information insert (PPI) when dispensing {01}.




Developed: 05/28/1998
Revised: 05/05/2000



References
  1. Viagra package insert (Pfizer—US), Rev 3/98, Rec 3/98.
  1. Canada JR, editor. USP dictionary of USAN and international drug names 1998. Rockville, MD: The United States Pharmacopeial Convention Inc; 1997. p. 666.
  1. Viagra package insert (Pfizer—US), Rev 11/98, Rec 12/98.
  1. Drug Information: Viagra™ (sildenafil). Pfizer Canada Inc., Kirkland, Quebec, Canada, Aug. 4, 1999, reviewed 1/2000.
  1. Drug Information: Viagra® (sildenafil). Pfizer Labs, New York, NY, (PI revised 6/99) reviewed 1/2000.
  1. Product Information Viagra® (sildenafil). Pfizer Labs, New York, NY, (PI revised 1/2000) reviewed 4/2000.
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