WARNINGS AND PRECAUTIONS

Side Effects
Pregnancy & Lactation
5.3 Epistaxis
4. Contraindications
What Other Drugs Interact with Sildenafil?
Further information
5.6 Combination with Other PDE-5 inhibitors

In a rat pre-and postnatal development study, the no-observed-adverse-effect dose was 30 mg/kg/day (equivalent to 5-times the RHD on a mg/m2 basis).

Patient Group	Recommended Dose	Frequency of Use	Notes
First-time users	20 mg	Once per day	Take 30-60 min before activity
Experienced users	May increase to 50 mg	As needed	Under medical supervision
Elderly patients	20 mg or lower	As needed	Start with lowest dose
Patients on other medications	Consult doctor	Varies	Adjust dose accordingly

Risk Summary Limited published data from a case report describe the presence of sildenafil and its active metabolite in human milk. Limited clinical data during lactation preclude a clear determination of the risk of sildenafil citrate to an infant during lactation. The safety and efficacy of Sildenafil citrate have been established in pediatric patients 1 to 17 years old, for the treatment of PAH (WHO Group I) to improve exercise ability and, in patients too young to perform standard exercising testing, pulmonary hemodynamics thought to underly improvements in exercise Use of sildenafil citrate for this indication is supported by evidence from adequate and well-controlled studies in adults with additional PK and safety data in pediatric patients aged 1 year and older [see Adverse Reactions (6.1), Clinical Studies (14)]. The safety and effectiveness of sildenafil citrate have not been established in pediatric patients younger than 1 year of age. During the conduct of the pediatric studies (STARTS-1 and STARTS-2) [see Clinical Studies(14)], an imbalance in the number of deaths was noted: 5/55 (9.1%), 10/74 (13.5%), and 22/100 (22%) in the sildenafil low, medium, and high dose groups, respectively.

Myths and misconceptions about sildenafil are common and should be addressed.
It is not a "party drug" or aphrodisiac; it requires sexual stimulation to work.
It does not cause spontaneous erections without sexual arousal.
More is not always better; higher doses increase side effect risk, not pleasure.
It is not addictive, but psychological dependence on its use can develop.
It does not permanently cure erectile dysfunction; effects are temporary.
It is not safe to use just because it is widely available or discussed.
Herbal "natural Viagra" products are not regulated and can be dangerous.
It does not protect against sexually transmitted infections or prevent pregnancy.
It is not approved or proven to enhance sexual performance in men without ED.
Accurate information from a healthcare provider is essential.

The causes of death were related to the progression of PAH. This safety observation in pediatrics was not confirmed in a study conducted in adults designed to evaluate this risk (Study A1481324). Given the beneficial effects on clinical worsening and death observed in adults with increasing doses (Study A1481324) and the expected similarity of disease in pediatrics and adults, a causal association for the observed dose-related effect on mortality in pediatric patients is unlikely, and therefore, the available data support dosing in pediatric patients >45 kg up to a maximum of 40 mg three times a day.

Side Effects

Changes from Baseline in Hemodynamic Parameters at Week 12 [mean (95% CI)] for the Sildenafil Tablets 20 mg Three Times a Day and Placebo Group mPAP = mean pulmonary arterial pressure; PVR= pulmonary vascular resistance; SVR = systemic vascular resistance; RAP = right atrial pressure; CO = cardiac output; HR = heart rate * The number of patients per treatment group varied slightly for each parameter due to missing assessments. Patients on sildenafil tablets medium and high dose groups achieved a dose related improvements in pulmonary vascular resistance index (PVRI) and mean pulmonary arterial pressure (mPAP) compared to those on placebo [see STARTS-1 in Clinical Studies (14)]. Improvements were observed with cardiac index in all three sildenafil tablets dose groups over placebo. Data on other hemodynamic measures for the sildenafil tablets low, medium and high dose groups compared to placebo is displayed in Table 3. Placebo Corrected Changes in Hemodynamic Parameters by Dose Group Abbreviations: CI = cardiac index; HR = heart rate; mPAP = mean pulmonary arterial pressure; PVRI = pulmonary vascular resistance index; RAP = right atrial pressure; SVRI = systemic vascular resistance index.

FAQs About Sildenafil Dosage

Note: n = 52, 56, 55, 54, 56, and 56 placebo patients for PVRI, mPAP, CI, SVRI, RAP and HR, respectively. Effects of Sildenafil Citrate on Blood Pressure Single oral doses of sildenafil 100 mg administered to healthy volunteers produced decreases in supine blood pressure (mean maximum decrease in systolic/diastolic blood pressure of 8/5 mmHg). The decrease in blood pressure was most notable approximately 1 to 2 hours after dosing and was not different from placebo at 8 hours. Similar effects on blood pressure were noted with 25 mg, 50 mg and 100 mg sildenafil premature ejaculation doses of sildenafil, therefore the effects are not related to dose or plasma levels within this dosage range. After chronic dosing of 80 mg three times a day sildenafil to patients with systemic hypertension, the mean change from baseline in systolic and diastolic blood pressures was a decrease of 9.4 mmHg and 9.1 mmHg, respectively. Clinical studies of sildenafil citrate did not include sufficient numbers of patients aged 65 and over to determine whether they respond differently from younger patients.

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Pregnancy & Lactation

Healthy elderly volunteers (65 years or over) had a reduced clearance of sildenafil, resulting in approximately 84% and 107% higher plasma concentrations of sildenafil and its active N-desmethyl metabolite, respectively, compared to those seen in healthy younger volunteers (18 to 45 years). In volunteers with mild (CLcr = 50 to 80 mL/min) and moderate (CLcr = 30 to 49 mL/min) renal impairment, the pharmacokinetics of a single oral dose of sildenafil (50 mg) was not altered. In volunteers with severe (CLcr less than 30 mL/min) renal impairment, sildenafil clearance was reduced, resulting in approximately doubling of AUC and C max compared to age-matched volunteers with no renal impairment. In addition, N-desmethyl metabolite AUC and C max values were significantly increased 200% and 79%, respectively, in patients with severe renal impairment compared to patients with normal renal function. In volunteers with mild to moderate hepatic cirrhosis (Child-Pugh class 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.

6.2 Postmarketing Experience

Patients with severe hepatic impairment (Child-Pugh class C) have not been studied. Sildenafil is a weak inhibitor of the cytochrome P450 isoforms 1A2, 2C9, 2C19, 2D6, 2E1 and 3A (IC 50 greater than 150 µM). 13.1 Carcinogenesis, Mutagenesis, Impairment of Fertility Sildenafil was not carcinogenic when administered to rats for up to 24 months at 60 mg/kg/day, a dose resulting in total systemic exposure (AUC) to unbound sildenafil and its major metabolite 33- and 37-times, for male and female rats, respectively, the human exposure at the RHD of 20 mg three times a day. Sildenafil was not carcinogenic when administered to male and female mice for up to 21 and 18 months, respectively, at doses up to a maximally tolerated level of 10 mg/kg/day, a dose equivalent to the RHD on a mg/m2 basis. Sildenafil was negative in in vitro bacterial and Chinese hamster ovary cell assays to detect mutagenicity, and in vitro human lymphocytes and in vivo mouse micronucleus assays to detect clastogenicity. Sildenafil is also marketed as VIAGRA® for erectile dysfunction. Sildenafil citrate, USP 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, USP 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. Sildenafil Tablets USP: Sildenafil citrate is formulated as white, film-coated round tablets for oral administration. In addition to the active ingredient, sildenafil citrate, each tablet contains the following inactive ingredients: croscarmellose sodium, dibasic calcium phosphate anhydrous, hypromellose, microcrystalline cellulose, sodium stearyl fumarate, titanium dioxide and triacetin. Its effect is more potent on PDE-5 than on other known phosphodiesterases (10-fold for PDE6, greater than 80-fold for PDE1, greater than 700-fold for PDE2, PDE3, PDE4, PDE7, PDE8, PDE9, PDE10, and PDE11). The approximately 4,000-fold selectivity for PDE5 versus PDE3 is important because PDE3 is involved in control of cardiac contractility. Sildenafil is only about 10-times as potent for PDE5 compared to PDE6, an enzyme found in the retina and involved in the phototransduction pathway of the retina. Effects of Sildenafil Citrate on Hemodynamic Measures Patients on all sildenafil citrate doses achieved a statistically significant reduction in mean pulmonary arterial pressure (mPAP) compared to those on chew sildenafil placebo in a study with no background vasodilators [see SUPER-1 in Clinical Studies (14)]. Data on other hemodynamic measures for the sildenafil tablets 20 mg three times a day and placebo dosing regimens is displayed in Table 2.

Sildenafil was originally developed to treat hypertension and angina.
Its effect lasts approximately 4-6 hours depending on individual factors.
Side effects may include muscle aches and skin rash in some cases.
Discuss all medications with your doctor to avoid harmful interactions.
Do not take sildenafil with fatty foods to ensure quicker action.

Country	Prescription Requirement	Over-the-Counter Availability	Regulatory Body
USA	Yes	No	FDA
UK	Yes	No	MHRA
Canada	Yes	No	Health Canada
Australia	Yes	No	TGA
India	Yes (in some states)	Some brands available OTC	CDSCO

Improvements were observed with cardiac index in all three sildenafil tablets dose groups over placebo. Data on other hemodynamic measures for the sildenafil tablets low, medium and high dose groups compared to placebo is displayed in Table 3. Placebo Corrected Changes in Hemodynamic Parameters by Dose Group Abbreviations: CI = cardiac index; HR = heart rate; mPAP = mean pulmonary arterial pressure; PVRI = pulmonary vascular resistance index; RAP = right atrial pressure; SVRI = systemic vascular resistance index. Note: n = 52, 56, 55, 54, 56, and 56 placebo patients for PVRI, mPAP, CI, SVRI, RAP and HR, respectively. Effects of Sildenafil Citrate on Blood Pressure Single oral doses of sildenafil 100 mg administered to healthy volunteers produced decreases in supine blood pressure (mean maximum decrease in systolic/diastolic blood pressure of 8/5 mmHg). The decrease in blood pressure was most notable approximately 1 to 2 hours after dosing and was not different from placebo at 8 hours. Similar effects on blood pressure were noted with 25 mg, 50 mg and 100 mg sildenafil premature ejaculation doses of sildenafil, therefore the effects are not related to dose or plasma levels within this dosage range. After chronic dosing of 80 mg three times a day sildenafil to patients with systemic hypertension, the mean change from baseline in systolic and diastolic blood pressures was a decrease of 9.4 mmHg and 9.1 mmHg, respectively. An evaluation of visual function at doses up to 200 mg revealed no effects of sildenafil citrate on visual acuity, intraocular pressure, or pupillometry. Sildenafil citrate is rapidly absorbed after oral administration, with a mean absolute bioavailability of 41% (25 to 63%). When sildenafil tablet is taken with a high-fat meal, the rate of absorption is reduced, with a mean delay in T max of 60 minutes and a mean reduction in Cmax of 29%. This metabolite has a phosphodiesterase selectivity profile similar to sildenafil and an in vitro potency for PDE-5 approximately 50% of the parent drug. In healthy volunteers, plasma concentrations of this metabolite are approximately 40% of those seen for sildenafil, so that the metabolite accounts for about 20% of sildenafil's pharmacologic effects. Both sildenafil and the active metabolite have terminal half-lives of about 4 hours. There was also a doubling of Cmin levels compared to healthy volunteers. Body weight was shown to be a good predictor of drug exposure in children.

5.3 Epistaxis

SUPER-1 (NCT00644605) - Sildenafil citrate monotherapy [20 mg, 40 mg, and 80 mg three times a day] A randomized, double-blind, placebo-controlled study of sildenafil citrate (SUPER-1) was conducted in 277 patients with PAH (defined as a mean pulmonary artery pressure≥25 mmHg at rest with a pulmonary capillary wedge pressure<15 mmHg). Patients were randomized to receive placebo (n=70) or sildenafil tablet 20 mg (n = 69), 40 mg (n = 67) or 80 mg (n = 71) three times a day for a period of 12 weeks.

Allergy warning

Sildenafil plasma concentration half-life values were estimated pfizer sildenafil 50 to range from 2.9 to 4.4 hours for a range of 10 to 70 kg of body weight. Tmax was estimated at approximately 1 hour. Healthy elderly volunteers (65 years or over) had a reduced clearance of sildenafil, resulting in approximately 84% and 107% higher plasma concentrations of sildenafil and its active N-desmethyl metabolite, respectively, compared to those seen in healthy younger volunteers (18 to 45 years). In volunteers with mild (CLcr = 50 to 80 mL/min) and moderate (CLcr = 30 to 49 mL/min) renal impairment, the pharmacokinetics of a single oral dose of sildenafil (50 mg) was not altered. In volunteers with severe (CLcr less than 30 mL/min) renal impairment, sildenafil clearance was reduced, resulting in approximately doubling of AUC and C max compared to age-matched volunteers with no renal impairment. In addition, N-desmethyl metabolite AUC and C max values were significantly increased 200% and 79%, respectively, in patients with severe renal impairment compared to patients with normal renal function. In volunteers with mild to moderate hepatic cirrhosis (Child-Pugh class 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.

4. Contraindications

In a rat pre-and postnatal development study, the no-observed-adverse-effect dose was 30 mg/kg/day (equivalent to 5-times the RHD on a mg/m2 basis). Risk Summary Limited published data from a case report describe the presence of sildenafil and its active metabolite in human milk. Limited clinical data during lactation preclude a clear determination of the risk of sildenafil citrate to an infant during lactation. The safety and efficacy of Sildenafil citrate have been established in pediatric patients 1 to 17 years old, for the treatment of PAH (WHO Group I) to improve exercise ability and, in patients too young to perform standard exercising testing, pulmonary hemodynamics thought to underly improvements in exercise Use of sildenafil citrate for this indication is supported by evidence from adequate and well-controlled studies in adults with additional PK and safety data in pediatric patients aged 1 year and older [see Adverse Reactions (6.1), Clinical Studies (14)]. The safety and effectiveness of sildenafil citrate have not been established in pediatric patients younger than 1 year of age.

Drugs you should not use with sildenafil

During the conduct of the pediatric studies (STARTS-1 and STARTS-2) [see Clinical Studies(14)], an imbalance in the number of deaths was noted: 5/55 (9.1%), 10/74 (13.5%), and 22/100 (22%) in the sildenafil low, medium, and high dose groups, respectively. The causes of death were related to the progression of PAH. This safety observation in pediatrics was not confirmed in a study conducted in adults designed to evaluate this risk (Study A1481324). Given the beneficial effects on clinical worsening and death observed in adults with increasing doses (Study A1481324) and the expected similarity of disease in pediatrics and adults, a causal association for the observed dose-related effect on mortality in pediatric patients is unlikely, and therefore, the available data support dosing in pediatric patients >45 kg up to a maximum of 40 mg three times a day. Clinical studies of sildenafil citrate did not include sufficient numbers of patients aged 65 and over to determine whether they respond differently from younger patients. Patients with severe hepatic impairment (Child-Pugh class C) have not been studied.

What Other Drugs Interact with Sildenafil?

Viagra Tablets

Sildenafil is a weak inhibitor of the cytochrome P450 isoforms 1A2, 2C9, 2C19, 2D6, 2E1 and 3A (IC 50 greater than 150 µM).

Further information

Sildenafil tablets, USP, phosphodiesterase-5 (PDE-5) inhibitor, is the citrate salt of sildenafil, a selective inhibitor of cyclic guanosine monophosphate (cGMP)-specific phosphodiesterase type-5 (PDE-5). Sildenafil is also marketed as VIAGRA® for erectile dysfunction. Sildenafil citrate, USP 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, USP 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. Sildenafil Tablets USP: Sildenafil citrate is formulated as white, film-coated round tablets for oral administration. In addition to the active ingredient, sildenafil citrate, each tablet contains the following inactive ingredients: croscarmellose sodium, dibasic calcium phosphate anhydrous, hypromellose, microcrystalline cellulose, sodium stearyl fumarate, titanium dioxide and triacetin.

7.4 Ritonavir and Other CYP3A4 Inhibitors

Its effect is more potent on PDE-5 than on other known phosphodiesterases (10-fold for PDE6, greater than 80-fold for PDE1, greater than 700-fold for PDE2, PDE3, PDE4, PDE7, PDE8, PDE9, PDE10, and PDE11). The approximately 4,000-fold selectivity for PDE5 versus PDE3 is important because PDE3 is involved in control of cardiac contractility. Sildenafil is only about 10-times as potent for PDE5 compared to PDE6, an enzyme found in the retina and involved in the phototransduction pathway of the retina. Effects of Sildenafil Citrate on Hemodynamic Measures Patients on all sildenafil citrate doses achieved a statistically significant reduction in mean pulmonary arterial pressure (mPAP) compared to those on chew sildenafil placebo in a study with no background vasodilators [see SUPER-1 in Clinical Studies (14)]. Data on other hemodynamic measures for the sildenafil tablets 20 mg three times a day and placebo dosing regimens is displayed in Table 2. 13.1 Carcinogenesis, Mutagenesis, Impairment of Fertility Sildenafil was not carcinogenic when administered to rats for up to 24 months at 60 mg/kg/day, a dose resulting in total systemic exposure (AUC) to unbound sildenafil and its major metabolite 33- and 37-times, for male and female rats, respectively, the human exposure at the RHD of 20 mg three times a day.

5.6 Combination with Other PDE-5 inhibitors

An evaluation of visual function at doses up to 200 mg revealed no effects of sildenafil citrate on visual acuity, intraocular pressure, or pupillometry. Sildenafil citrate is rapidly absorbed after oral administration, with a mean absolute bioavailability of 41% (25 to 63%). When sildenafil tablet is taken with a high-fat meal, the rate of absorption is reduced, with a mean delay in T max of 60 minutes and a mean reduction in Cmax of 29%. This metabolite has a phosphodiesterase selectivity profile similar to sildenafil and an in vitro potency for PDE-5 approximately 50% of the parent drug. In healthy volunteers, plasma concentrations of this metabolite are approximately 40% of those seen for sildenafil, so that the metabolite accounts for about 20% of sildenafil's pharmacologic effects.

Usual Geriatric Dose for:

Both sildenafil and the active metabolite have terminal half-lives of about 4 hours. There was also a doubling of Cmin levels compared to healthy volunteers. Body weight was shown to be a good predictor of drug exposure in children. Sildenafil plasma concentration half-life values were estimated pfizer sildenafil 50 to range from 2.9 to 4.4 hours for a range of 10 to 70 kg of body weight. Tmax was estimated at approximately 1 hour. Sildenafil was not carcinogenic when administered to male and female mice for up to 21 and 18 months, respectively, at doses up to a maximally tolerated level of 10 mg/kg/day, a dose equivalent to the RHD on a mg/m2 basis. Sildenafil was negative in in vitro bacterial and Chinese hamster ovary cell assays to detect mutagenicity, and in vitro human lymphocytes and in vivo mouse micronucleus assays to detect clastogenicity. SUPER-1 (NCT00644605) - Sildenafil citrate monotherapy [20 mg, 40 mg, and 80 mg three times a day] A randomized, double-blind, placebo-controlled study of sildenafil citrate (SUPER-1) was conducted in 277 patients with PAH (defined as a mean pulmonary artery pressure≥25 mmHg at rest with a pulmonary capillary wedge pressure<15 mmHg). Patients were randomized to receive placebo (n=70) or sildenafil tablet 20 mg (n = 69), 40 mg (n = 67) or 80 mg (n = 71) three times a day for a period of 12 weeks.

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