[1] These doses in rats and rabbits represent about 16 and 32 times, respectively, the maximum recommended human dose (MRHD) for the treatment of ED on a mg/m2 basis in a 50-kg patient.

Brand Name	Manufacturer	Formulation Type	Typical Dosage	Notes
Viagra	Pfizer	Tablet	25, 50, 100 mg	Most well-known brand
Revatio	Pfizer	Tablet	20 mg	For pulmonary hypertension
Sildenafil Citrate	Various generic manufacturers	Tablet	25, 50, 100 mg	Generic versions available
Kamagra	Ajanta Pharma	Oral Gel	100 mg	Used off-label in some countries

[1] No adverse effects were observed Iin a prenatal and postnatal development study in rats receiving 30 mg/kg daily for 36 days (equivalent to 2-times the MRHD on a mg/m2 basis in a 50-kg subject). [1] Limited data indicate that sildenafil and its active metabolite are present in human milk. [1] There is no information about the effects of sildenafil on the breastfed infant or on milk production.

Parameter	Description	Typical Value
Absorption Rate	Time to reach peak plasma concentration	30-120 minutes
Bioavailability	Percentage of dose reaching systemic circulation	40%
Half-life	Time to reduce plasma concentration by half	4 hours
Metabolism	Primary site of metabolism	Liver (CYP3A4 enzyme)
Excretion	Main routes of elimination	Feces and urine

Reproduction studies revealed no evidence of impaired fertility at sildenafil dosages up to 60 mg/kg daily (for 36 days in female rats and 102 days in male rats), a dosage representing more than 25 times the human male AUC. [1] No effect on sperm motility or morphology was noted after a single 100-mg oral sildenafil dose in healthy human adults.

What special dietary instructions should I follow?

[1] These doses in rats and rabbits represent about 16 and 32 times, respectively, the maximum recommended human dose (MRHD) for the treatment of ED on a mg/m2 basis in a 50-kg patient. [1] No adverse effects were observed Iin a prenatal and postnatal development study in rats receiving 30 mg/kg daily for 36 days (equivalent to 2-times the MRHD on a mg/m2 basis in a 50-kg subject). [1] Limited data indicate that sildenafil and its active metabolite are present in human milk. [1] There is no information about the effects of sildenafil on the breastfed infant or on milk production. Reproduction studies revealed no evidence of impaired fertility at sildenafil dosages up to 60 mg/kg daily (for 36 days in female rats and 102 days in male rats), a dosage representing more than 25 times the human male AUC.

Clinical monitoring

[1] No effect on sperm motility or morphology was noted after a single 100-mg oral sildenafil dose in healthy human adults. Sildenafil for ED (e.g., Viagra®) is not indicated for use in pediatric patients. [1] The manufacturer states that safety and efficacy of sildenafil in children have not been established. The AUC of free (unbound) sildenafil and its active N-desmethyl metabolite were 45 and 57% higher, respectively, in healthy volunteers >=65 years of age compared to healthy volunteers 18-45 years of age. [1] Clinical studies included patients >=65 years of age (18%) and >=75 years of age (2%); no overall differences in safety and efficacy were observed between older (>=65 years of age) and younger (<65 years of age) patients[1] Because higher plasma levels may increase the incidence of adverse reactions, consider reducing the initial sildenafil dosage to 25 mg in older patients. Sildenafil for ED (e.g., Viagra®) is not indicated for use in pediatric patients. [1] The manufacturer states that safety and efficacy of sildenafil in children have not been established.

Product	Dosage	Quantity + Bonus	Price
Viagra Generic	50mg	120 + 6 Pills	129.64€ 123.47€
Kamagra Oral Jelly	100mg	63 + 7 Sachets	224.18€ 213.50€
Viagra Generic	200mg	270 + 10 Pills	379.76€ 361.68€
Kamagra Polo	100mg	180 + 8 Pills	446.52€ 425.26€
Kamagra Soft Tabs	100mg	84 + 4 Pills	233.05€ 221.95€
Kamagra Soft Tabs	100mg	20 Pills	79.79€ 75.99€
Viagra Generic	150mg	270 + 10 Pills	326.61€ 311.06€
Viagra Generic	200mg	120 + 8 Pills	204.80€ 195.05€
Kamagra Soft Tabs	100mg	180 + 8 Pills	425.45€ 405.19€
Kamagra Oral Jelly	100mg	220 + 18 Sachets	662.24€ 630.70€
Viagra Generic	200mg	360 + 10 Pills	481.98€ 459.03€
Viagra Generic	100mg	90 + 6 Pills	129.02€ 122.88€
Kamagra Soft Tabs	100mg	12 Pills	57.55€ 54.81€
Viagra Generic	50mg	270 + 8 Pills	198.48€ 189.03€
Kamagra Polo	100mg	84 + 4 Pills	244.49€ 232.85€
Viagra Generic	200mg	180 + 10 Pills	277.56€ 264.34€

The AUC of free (unbound) sildenafil and its active N-desmethyl metabolite were 45 and 57% higher, respectively, in healthy volunteers >=65 years of age compared to healthy volunteers 18-45 years of age. [1] Clinical studies included patients >=65 years of age (18%) and >=75 years of age (2%); no overall differences in safety and efficacy were observed between older (>=65 years of age) and younger (<65 years of age) patients[1] Because higher plasma levels may increase the incidence of adverse reactions, consider reducing the initial sildenafil dosage to 25 mg in older patients. In patients with hepatic cirrhosis (Child-Pugh class A or B), sildenafil clearance is reduced, resulting in increased AUC (by 85%) and peak plasma concentrations (by 47%) compared with values observed in age-matched healthy adults. [1][31][131] The effect of severe hepatic impairment on the pharmacokinetics of sildenafil has not been evaluated to date. In patients with any degree of hepatic impairment (e.g. cirrhosis), consider reducing the initial dose of sildenafil to 25 mg.[1] In patients with mild (creatinine clearance 50-80 mL/minute) or moderate (creatinine clearance 30-49 mL/minute) renal impairment, the pharmacokinetics of a single 50-mg oral dose of sildenafil are not altered. [1][31][131] However, in patients with severe (creatinine clearance less than 30 mL/minute) renal impairment, sildenafil clearance is reduced, resulting in AUC and peak plasma concentrations of the parent drug that are approximately double those in age-matched healthy adults. [1][31][67][131] In addition, AUC and peak plasma concentrations of the N-demethylated metabolite are 200 and 79% greater, respectively, than those in individuals with normal renal function. In patients with severe renal impairment (creatinine clearance less than 30 mL/minute), consider reducing the initial dose of sildenafil to 25 mg.[1] The most common adverse effects (>=2%) of sildenafil used for the treatment of ED include headache, flushing, dyspepsia, abnormal vision, nasal congestion, back pain, myalgia, nausea, dizziness, and rash.

Look-Alike Drug Names

Sildenafil 50 mg did not potentiate the hypotensive effect of alcohol (0.5 g/kg) in healthy individuals (mean maximum blood alcohol concentrations of 0.08% achieved). Sildenafil has systemic vasodilatory effects and may augment the blood pressure-lowering effect of other antihypertensive agents. [1] Hypotensive responses secondary to sildenafil use in patients receiving antihypertensive therapy have been observed. The risk of an undesired hypotensive response is of particular concern in patients with congestive heart failure and a borderline low blood volume and low blood pressure status as well as in patients with left-ventricular outflow obstruction (e.g., aortic stenosis, idiopathic hypertrophic subaortic stenosis), those with severely impaired autonomic control of blood pressure, and in those who are receiving a complex, multidrug antihypertensive regimen. The AUC of the active metabolite, N-desmethyl sildenafil, was increased 62% by loop and potassium-sparing diuretics and 102% by nonspecific β-adrenergic blocking agents; however, the increased active metabolite concentrations are not expected to be clinically important.

What should I do if I miss a dose of sildenafil?

Additive hypotensive effects may be anticipated when PDE type 5 inhibitors are administered concurrently with α-adrenergic blocking agents (e.g., terazosin, doxazosin, tamsulosin). [1] Stepwise increases in the dosage of the α-adrenergic blocking agent may further lower blood pressure when a PDE type 5 inhibitor is administered concurrently. [1] In several placebo-controlled crossover studies in patients with benign prostatic hyperplasia receiving doxazosin (4 or 8 mg daily) under steady-state conditions, administration of a single dose of sildenafil (50 or 100 mg) resulted in symptomatic hypotension (e.g., dizziness, lightheadedness, nausea, headache, fatigue) in some patients, occurring within approximately 0.5-4 hours of sildenafil administration. [1] Although symptomatic hypotension occurred in a few patients who received sildenafil 50 or 100 mg, syncope was not reported during these drug interaction studies. Sildenafil is metabolized principally via hepatic cytochrome P-450 (CYP) microsomal isoenzymes 3A4 (major route) and 2C9 (minor route). [1][91][131] Inhibitors and inducers of these isoenzymes may reduce or increase sildenafil clearance, respectively. In vitro studies indicate that sildenafil is a weak inhibitor of the CYP isoenzymes 1A2, 2C9, 2C19, 2D6, 2E1, and 3A4. [1][26][67][250] Sildenafil is not expected to affect the pharmacokinetics of substrates of these CYP enzymes at clinically relevant concentrations.

6. Response and effectiveness

Cimetidine: Plasma sildenafil concentrations increased by approximately 56% in healthy individuals who received a single 50-mg oral dose of the drug concomitantly with a single oral dose of cimetidine (800 mg), a nonspecific inhibitor of the cytochrome P-450 mixed-function oxidase system. [1][67] Population pharmacokinetic analysis of data from clinical trials indicates that cimetidine reduces sildenafil clearance when these drugs are administered concomitantly. [1][139] Some clinicians recommend that a lower initial sildenafil dose (25 mg) be considered in patients with ED receiving cimetidine. Concomitant use of any form of organic nitrate (e.g., nitroglycerin), including recreational use of inhaled nitrites (amyl nitrate or nitrite, ''poppers''), with sildenafil is contraindicated due to the potential pharmacodynamic interaction (increased hypotensive effect). However, the American College of Cardiology (ACC) and American Heart Association (AHA) recognize that use of organic nitrates and nitrites in patients receiving sildenafil may not be completely avoidable, provided sufficient time has elapsed between use of sildenafil and administration of the nitrate or nitrite.

What’s the youngest age for which Viagra is safe to use?

[67] Although it is not known how much time must elapse between use of sildenafil and administration of a nitrate or nitrite, pharmacokinetic data suggest that these latter agents should not be given within 24 hours of sildenafil administration because an exaggerated hypotensive response is likely; plasma sildenafil concentrations are substantially lower 24 hours after a dose than peak concentrations. [1][29][31][67] The point at which nitrates or nitrites can be given safely is unclear, and therefore the drugs should be avoided unless, in the view of the treating clinician, the benefits outweigh the risks. If consideration is given to administering a nitrate or nitrite beyond 24 hours after sildenafil use, the response to the initial doses must be monitored carefully and proper facilities for fluid and vasopressor (e.g., α-adrenergic agonists) support must be readily available to prevent acute ischemic episodes. [67][159] In patients in whom clearance of sildenafil and/or its metabolites may be prolonged (e.g., those with hepatic [e.g., cirrhosis] or severe renal impairment [e.g., creatinine clearance less than 30 mL/minute], those receiving a potent inhibitor of CYP3A4, geriatric patients older than 65 years of age), a more extended period of time between use of sildenafil and administration of a nitrate or nitrite may be necessary. [1][67][154] In either case, a short-acting nitrate formulation that can be titrated readily (e.g., IV nitroglycerin) is preferred and such use should be accompanied by close hemodynamic monitoring. The possibility that any drug that inhibits CYP3A4 may interact with sildenafil should be considered. [1][67] In some cases, a reduction in sildenafil dosage is recommended. Clinically important pharmacokinetic interactions have been reported with several antiretroviral agents that inhibit CYP3A4 (e.g., ritonavir, saquinavir) and can potentially result in an increase in sildenafil-associated adverse effects. The possibility that any drug that induces CYP3A4 may interact with sildenafil should be considered. Pharmacokinetic data from patients in clinical trials showed no effect sildenafil citrate 100mg tablets on sildenafil pharmacokinetics when the drug was used concomitantly with CYP2D6 inhibitors such as selective serotonin-reuptake inhibitors (SSRIs) or tricyclic antidepressants. [1] [26][67] At clinically relevant concentrations, the manufacturer states that it is unlikely that sildenafil will alter the clearance of drugs metabolized by these isoenzymes. A minor route of metabolism of sildenafil is through the CYP2C9 isoenzyme. [1][67][250] Although some clinicians state that the possibility of an interaction between sildenafil and drugs metabolized by CYP2C9 should be considered, there was no evidence of appreciable inhibition of CYP2C9-mediated (e.g., tolbutamide, warfarin) or CYP3A4-mediated (e.g., ritonavir, saquinavir) metabolism by sildenafil in clinical studies. **Antacids:**Single doses of an aluminum and magnesium hydroxide-containing antacid did not affect the oral bioavailability of sildenafil. Cimetidine: Plasma sildenafil concentrations increased by approximately 56% in healthy individuals who received a single 50-mg oral dose of the drug concomitantly with a single oral dose of cimetidine (800 mg), a nonspecific inhibitor of the cytochrome P-450 mixed-function oxidase system. [1][67] Population pharmacokinetic analysis of data from clinical trials indicates that cimetidine reduces sildenafil clearance when these drugs are administered concomitantly. [1][139] Some clinicians recommend that a lower initial sildenafil dose (25 mg) be considered in patients with ED receiving cimetidine. Concomitant use of any form of organic nitrate (e.g., nitroglycerin), including recreational use of inhaled nitrites (amyl nitrate or nitrite, ''poppers''), with sildenafil is contraindicated due to the potential pharmacodynamic interaction (increased hypotensive effect).

The medication is classified as a controlled substance in some jurisdictions.
Over-reliance on sildenafil without addressing underlying causes is discouraged.
Psychological counseling may benefit some patients with ED.
Detailed medical history helps determine if sildenafil is safe.
Education on possible side effects improves patient safety.
The drug does not cause dependency.
Proper use ensures maximum therapeutic benefit and safety.

However, the American College of Cardiology (ACC) and American Heart Association (AHA) recognize that use of organic nitrates and nitrites in patients receiving sildenafil may not be completely avoidable, provided sufficient time has elapsed between use of sildenafil and administration of the nitrate or nitrite.

1. How it works

In patients with hepatic cirrhosis (Child-Pugh class A or B), sildenafil clearance is reduced, resulting in increased AUC (by 85%) and peak plasma concentrations (by 47%) compared with values observed in age-matched healthy adults. [1][31][131] The effect of severe hepatic impairment on the pharmacokinetics of sildenafil has not been evaluated to date. In patients with any degree of hepatic impairment (e.g. cirrhosis), consider reducing the initial dose of sildenafil to 25 mg.[1] In patients with mild (creatinine clearance 50-80 mL/minute) or moderate (creatinine clearance 30-49 mL/minute) renal impairment, the pharmacokinetics of a single 50-mg oral dose of sildenafil are not altered. [1][31][131] However, in patients with severe (creatinine clearance less than 30 mL/minute) renal impairment, sildenafil clearance is reduced, resulting in AUC and peak plasma concentrations of the parent drug that are approximately double those in age-matched healthy adults.

Common Side Effects

[1][31][67][131] In addition, AUC and peak plasma concentrations of the N-demethylated metabolite are 200 and 79% greater, respectively, than those in individuals with normal renal function. In patients with severe renal impairment (creatinine clearance less than 30 mL/minute), consider reducing the initial dose of sildenafil to 25 mg.[1] The most common adverse effects (>=2%) of sildenafil used for the treatment of ED include headache, flushing, dyspepsia, abnormal vision, nasal congestion, back pain, myalgia, nausea, dizziness, and rash. Sildenafil is metabolized principally via hepatic cytochrome P-450 (CYP) microsomal isoenzymes 3A4 (major route) and 2C9 (minor route). [1][91][131] Inhibitors and inducers of these isoenzymes may reduce or increase sildenafil clearance, respectively. In vitro studies indicate that sildenafil is a weak inhibitor of the CYP isoenzymes 1A2, 2C9, 2C19, 2D6, 2E1, and 3A4. [67] Although it is not known how much time must elapse between use of sildenafil and administration of a nitrate or nitrite, pharmacokinetic data suggest that these latter agents should not be given within 24 hours of sildenafil administration because an exaggerated hypotensive response is likely; plasma sildenafil concentrations are substantially lower 24 hours after a dose than peak concentrations.

Sildenafil is available in most countries through prescription only.
It is used worldwide, with varying approval statuses.
FDA and EMA have rigorous testing standards for sildenafil.
Using the drug responsibly can lead to successful treatment outcomes.
Combining sildenafil with other medications requires medical supervision.
Be aware of the potential for drug interactions with heart or blood pressure meds.
Always consult a healthcare professional for personalized advice.

[1][29][31][67] The point at which nitrates or nitrites can be given safely is unclear, and therefore the drugs should be avoided unless, in the view of the treating clinician, the benefits outweigh the risks.

What Are Side Effects Associated with Using Sildenafil?

[1][26][67][250] Sildenafil is not expected to affect the pharmacokinetics of substrates of these CYP enzymes at clinically relevant concentrations. The possibility that any drug that inhibits CYP3A4 may interact with sildenafil should be considered. [1][67] In some cases, a reduction in sildenafil dosage is recommended. Clinically important pharmacokinetic interactions have been reported with several antiretroviral agents that inhibit CYP3A4 (e.g., ritonavir, saquinavir) and can potentially result in an increase in sildenafil-associated adverse effects. The possibility that any drug that induces CYP3A4 may interact with sildenafil should be considered.

What are the most common side effects of sildenafil?

Pharmacokinetic data from patients in clinical trials showed no effect sildenafil citrate 100mg tablets on sildenafil pharmacokinetics when the drug was used concomitantly with CYP2D6 inhibitors such as selective serotonin-reuptake inhibitors (SSRIs) or tricyclic antidepressants. [1] [26][67] At clinically relevant concentrations, the manufacturer states that it is unlikely that sildenafil will alter the clearance of drugs metabolized by these isoenzymes. A minor route of metabolism of sildenafil is through the CYP2C9 isoenzyme. [1][67][250] Although some clinicians state that the possibility of an interaction between sildenafil and drugs metabolized by CYP2C9 should be considered, there was no evidence of appreciable inhibition of CYP2C9-mediated (e.g., tolbutamide, warfarin) or CYP3A4-mediated (e.g., ritonavir, saquinavir) metabolism by sildenafil in clinical studies. **Antacids:**Single doses of an aluminum and magnesium hydroxide-containing antacid did not affect the oral bioavailability of sildenafil. If consideration is given to administering a nitrate or nitrite beyond 24 hours after sildenafil use, the response to the initial doses must be monitored carefully and proper facilities for fluid and vasopressor (e.g., α-adrenergic agonists) support must be readily available to prevent acute ischemic episodes. [67][159] In patients in whom clearance of sildenafil and/or its metabolites may be prolonged (e.g., those with hepatic [e.g., cirrhosis] or severe renal impairment [e.g., creatinine clearance less than 30 mL/minute], those receiving a potent inhibitor of CYP3A4, geriatric patients older than 65 years of age), a more extended period of time between use of sildenafil and administration of a nitrate or nitrite may be necessary. [1][67][154] In either case, a short-acting nitrate formulation that can be titrated readily (e.g., IV nitroglycerin) is preferred and such use should be accompanied by close hemodynamic monitoring. Sildenafil 50 mg did not potentiate the hypotensive effect of alcohol (0.5 g/kg) in healthy individuals (mean maximum blood alcohol concentrations of 0.08% achieved). Sildenafil has systemic vasodilatory effects and may augment the blood pressure-lowering effect of other antihypertensive agents. [1] Hypotensive responses secondary to sildenafil use in patients receiving antihypertensive therapy have been observed.

What is sildenafil?

The risk of an undesired hypotensive response is of particular concern in patients with congestive heart failure and a borderline low blood volume and low blood pressure status as well as in patients with left-ventricular outflow obstruction (e.g., aortic stenosis, idiopathic hypertrophic subaortic stenosis), those with severely impaired autonomic control of blood pressure, and in those who are receiving a complex, multidrug antihypertensive regimen. The AUC of the active metabolite, N-desmethyl sildenafil, was increased 62% by loop and potassium-sparing diuretics and 102% by nonspecific β-adrenergic blocking agents; however, the increased active metabolite concentrations are not expected to be clinically important. Additive hypotensive effects may be anticipated when PDE type 5 inhibitors are administered concurrently with α-adrenergic blocking agents (e.g., terazosin, doxazosin, tamsulosin). [1] Stepwise increases in the dosage of the α-adrenergic blocking agent may further lower blood pressure when a PDE type 5 inhibitor is administered concurrently. [1] In several placebo-controlled crossover studies in patients with benign prostatic hyperplasia receiving doxazosin (4 or 8 mg daily) under steady-state conditions, administration of a single dose of sildenafil (50 or 100 mg) resulted in symptomatic hypotension (e.g., dizziness, lightheadedness, nausea, headache, fatigue) in some patients, occurring within approximately 0.5-4 hours of sildenafil administration. [1] Although symptomatic hypotension occurred in a few patients who received sildenafil 50 or 100 mg, syncope was not reported during these drug interaction studies.

Storage and Handling Guidelines