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In cases of overdose, standard supportive measures should be adopted as required. Renal dialysis is not expected to accelerate clearance as sildenafil is highly bound to plasma proteins and it is not eliminated in the urine.

VIAGRA (sildenafil citrate), an oral therapy for erectile dysfunction, is the citrate salt of sildenafil, a selective inhibitor of cyclic guanosine monophosphate (cGMP)-specific phosphodiesterase type 5 (PDE5). Sildenafil citrate is designated chemically as 1-[[3-(6,7-dihydro-1-methyl-7-oxo-3-propyl-1 H -pyrazolo[4,3- d ]pyrimidin-5-yl)-4-ethoxyphenyl]sulfonyl]-4-methylpiperazine citrate and has the following structural formula: Sildenafil citrate is a white to off-white crystalline powder with a solubility of 3.5 mg/mL in water and a molecular weight of 666.7.

VIAGRA is formulated as blue, film-coated rounded-diamond-shaped tablets equivalent to 25 mg, 50 mg and 100 mg of

sildenafil

oral

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 enhances the effect of NO by inhibiting phosphodiesterase type 5 (PDE5), which is responsible for degradation of cGMP in the corpus cavernosum.

Sildenafil has no direct relaxant effect on isolated human 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.

Studies in vitro have shown that sildenafil is selective for PDE5.

Its effect is more potent on PDE5 than on other known phosphodiesterases (10-fold for PDE6, >80-fold for PDE1, >700-fold for PDE2, PDE3, PDE4, PDE7, PDE8, PDE9, PDE10, and PDE11).

Sildenafil is approximately 4,000-fold more selective for PDE5 compared to PDE3.

PDE3 is involved in control of cardiac contractility.

Sildenafil is only about 10-fold as potent for PDE5 compared to PDE6, an enzyme found in the retina which is involved in the

phototransduction

This lower selectivity is thought to be the

basis

In addition to human corpus cavernosum smooth muscle, PDE5 is also found in other tissues including platelets, vascular pfizer online store and visceral smooth muscle, and skeletal muscle, brain, heart, liver, kidney, lung, pancreas, prostate, bladder, testis, and seminal vesicle.

The inhibition of PDE5 in some of these tissues by sildenafil may be the basis for the enhanced platelet antiaggregatory activity of NO observed in vitro , an inhibition of platelet thrombus formation in vivo and peripheral arterial-venous dilatation in vivo .

Effects of VIAGRA on Erectile Response: In eight double-blind, placebo-controlled crossover studies of patients with either organic or psychogenic erectile dysfunction, sexual stimulation resulted in improved erections, as assessed by an objective measurement of hardness and duration of erections (RigiScan ® ), after VIAGRA administration compared with placebo. Most studies assessed the efficacy of VIAGRA approximately 60 minutes post dose. The erectile response, as assessed by RigiScan ® , generally increased with increasing sildenafil dose and plasma concentration. The time course sildenafil citrate over the counter walgreens of effect was examined in one study, showing an effect for up to 4 hours but the response was diminished compared to 2 hours.

Effects of VIAGRA on Blood Pressure: Single oral doses of sildenafil (100 mg) administered to healthy volunteers produced decreases in sitting blood pressure (mean maximum decrease in systolic/diastolic blood pressure of 8.3/5.3 mmHg).

The decrease in sitting blood pressure was most notable approximately 1–2 hours after dosing, and was not different than placebo at 8 hours.

Similar effects on blood pressure were noted with 25 mg, 50 mg and 100 mg of VIAGRA, therefore the effects are not related to dose or plasma levels within this dosage range.

Larger effects were recorded among patients receiving concomitant nitrates [ see Contraindications (4.1) ]. Figure 1: Mean Change from Baseline in Sitting Systolic Blood Pressure, Healthy Volunteers. Effects of VIAGRA on Blood Pressure When Nitroglycerin is Subsequently Administered: Based on the pharmacokinetic profile of a single 100 mg oral dose given to healthy normal volunteers, the plasma levels of sildenafil at 24 hours post dose are approximately 2 ng/mL (compared to peak plasma levels of approximately 440 ng/mL). In the following patients: age >65 years, hepatic impairment (e.g., cirrhosis), severe renal impairment (e.g., creatinine clearance see Contraindications (4.1) ]. Effects of VIAGRA on Blood Pressure When Co-administered with Alpha-Blockers: Three double-blind, placebo-controlled, randomized, two-way crossover studies were conducted to assess the interaction of VIAGRA with doxazosin, an alpha-adrenergic blocking agent.

In the first study, a single oral dose of VIAGRA 100 mg or matching placebo was administered in a 2-period crossover design to 4 generally healthy males with benign prostatic hyperplasia (BPH).

Following at least 14 consecutive daily doses of doxazosin, VIAGRA 100 mg or matching placebo was administered simultaneously with doxazosin. Following a review of the data from these first 4 subjects (details provided below), the VIAGRA dose was reduced to 25 mg. Thereafter, 17 subjects were treated with VIAGRA 25 mg or matching placebo in combination with doxazosin 4 mg (15 subjects) or doxazosin 8 mg (2 subjects). For the 17 subjects who received VIAGRA 25 mg and matching placebo, the placebo-subtracted mean maximum decreases from baseline (95% CI) in systolic blood pressure were as follows: Placebo-subtracted mean maximum decrease in systolic blood pressure (mm Hg) VIAGRA 25 mg Supine 7.4 (-0.9 , 15.7) Standing 6.0 (-0.8, 12.8) The mean profiles of the change from baseline in standing systolic blood pressure in subjects treated with doxazosin in combination with 25 mg VIAGRA or matching placebo are shown in Figure 2. Figure 2: Mean Standing Systolic Blood Pressure Change from Baseline. Blood pressure was measured immediately pre-dose and at 15, 30, 45 minutes, and 1, 1.5, 2, 2.5, 3, 4, 6 and 8 hours after VIAGRA or matching placebo.

Outliers were defined as subjects with a standing systolic blood pressure of 30 mmHg at one or more timepoints. There were no subjects treated with VIAGRA 25 mg who had a standing online cialis us SBP 30mmHg following VIAGRA 25 mg, one subject with a decrease from baseline in standing systolic BP > 30 mmHg following placebo and two subjects with a decrease from baseline in standing systolic BP > 30 mmHg following both VIAGRA and placebo. No severe adverse events potentially related to blood pressure effects were reported in this group. Of the four subjects who received VIAGRA 100 mg in the first part of this study, a severe adverse event related to blood pressure effect was reported in one patient (postural hypotension that began 35 minutes after dosing with VIAGRA with symptoms lasting for 8 hours), and mild adverse events potentially related to blood pressure effects were reported in two others (dizziness, headache and

fatigue

There were no reports of syncope among these patients. For these four subjects, the placebo-subtracted mean maximum decreases from baseline in supine and standing systolic blood pressures were 14.8 mmHg and 21.5 mmHg, respectively. Two of these subjects had a standing SBP Study 2: VIAGRA with Doxazosin. In the second study, a single oral dose of VIAGRA 50 mg or matching placebo was administered in a 2-period crossover design to 20 generally healthy males with BPH.

Following at least 14 consecutive days of doxazosin, VIAGRA 50 mg or matching placebo was administered simultaneously with doxazosin 4 mg (17 subjects) or with doxazosin 8 mg (3 subjects). Twenty subjects received VIAGRA 50 mg, but only 19 subjects received matching placebo.

One patient discontinued the study prematurely due to an adverse event of hypotension following dosing with VIAGRA 50 mg. This patient had been taking minoxidil, a potent vasodilator, during the study. For the 19 subjects who received both VIAGRA and matching placebo, the placebo-subtracted mean maximum decreases from baseline (95% CI) in systolic blood pressure were as follows: Placebo-subtracted mean maximum decrease in systolic blood pressure (buy sildenafil online cheap mm Hg)

VIAGRA

the

There were two subjects who had a standing SBP of 30mmHg following VIAGRA 50 mg and one subject with a decrease from baseline in standing systolic BP > 30 mmHg following both VIAGRA 50 mg and placebo.

There were no severe adverse events potentially related to blood pressure and no episodes of syncope reported in this study. In the third study, a single oral dose of VIAGRA 100 mg or matching placebo was administered in a 3-period

crossover

If a subject did not successfully complete this first dosing period, he was discontinued from the study.

Subjects who had successfully completed the previous doxazosin interaction study (using VIAGRA 50 mg), including no significant hemodynamic adverse events, were allowed to skip dose period 1. Treatment with doxazosin continued for at least 7 days after dose period 1. Thereafter, VIAGRA 100 mg or matching placebo was administered simultaneously with doxazosin 4 mg (14 subjects) or doxazosin 8 mg (6 subjects) in standard crossover fashion. Two were discontinued after study period 1: one failed to meet pre-dose screening qualifications and the other experienced symptomatic hypotension as a moderately severe adverse event 30 minutes after dosing with open-label VIAGRA 50 mg.

Of the twenty subjects who were ultimately assigned to treatment, a total of 13 subjects successfully completed dose period 1, and seven had successfully completed the previous doxazosin study (using VIAGRA 50 mg).

For the 20 subjects who received VIAGRA 100 mg and matching placebo, the placebo-subtracted mean maximum decreases from baseline (95% CI) in systolic blood pressure were as follows: Placebo-subtracted mean maximum decrease in systolic blood pressure (mm Hg) VIAGRA 100 mg Supine 7.9 (4.6, 11.1) Standing 4.3 (-1.8,10.3) The mean profiles of the change from baseline in standing systolic blood pressure in subjects treated with doxazosin in combination with 100 mg VIAGRA or matching placebo are shown in Figure 4. Figure 4: Mean Standing Systolic Blood Pressure Change from Baseline.

Blood pressure was measured after administration of VIAGRA at the same times as those specified for the previous doxazosin studies.

There were three subjects who had a standing SBP of 30 mmHg following VIAGRA 100 mg, one subject with a decrease from baseline in standing systolic BP > 30 mmHg following placebo and one subject with a decrease from baseline in standing systolic BP > 30 mmHg following both VIAGRA and placebo.

While

and

There were no episodes of syncope reported in this study. Effect of VIAGRA on Blood Pressure When Co-administered with Anti-hypertensives: When VIAGRA 100 mg oral was co-administered with amlodipine, 5 mg or 10 mg oral, to hypertensive patients, the mean additional reduction on supine blood pressure was 8 mmHg systolic and 7 mmHg diastolic.

Effect of VIAGRA on Blood Pressure When Co-administered with Alcohol: VIAGRA (50 mg) did not potentiate the hypotensive effect of alcohol (0.5 g/kg) in healthy volunteers with mean maximum blood alcohol levels of 0.08%. The maximum observed decrease in systolic blood pressure was -18.5 mmHg when sildenafil was co-administered with alcohol versus -17.4 mmHg when alcohol was administered alone.