Description

Viagra also contains the following excipients: Microcrystalline cellulose, anhydrous calcium hydrogen phosphate, croscarmellose sodium, magnesium stearate, hydroxypropyl methylcellulose (hypromellose), titanium dioxide (E171), lactose, triacetin and FD&C blue #2 aluminum lake [indigo carmine aluminum lake (E132).

 

Presentation / Packing

100 mg (blue, rounded diamond-shaped, marked "PFIZER" on one side and "VGR 100" on the other) x 4 .

 

Dosage / Direction for Use

100 mg approx 1 hr before sexual activity. May be decreased to 25 mg. Max: 100 mg. Max dosing frequency is once/day. 

Manufacturer

Pfizer (Thailand) Ltd

 

Distributor

 

Distributor For : 2M (Med-Maker),A.Menarini,Abbott Nutrition

 

Contents

Sildenafil citrate

 

Indications / Uses

Treatment of erectile dysfunction, which is the inability to achieve or maintain a penile erection sufficient for satisfactory sexual performance.
In order for sildenafil to be effective, sexual stimulation is required.

 

Dosage / Direction for Use

100 mg approx 1 hr before sexual activity. May be increased to 100 mg or decreased to 25 mg. Max: 100 mg. Max dosing frequency is once/day. 
Sildenafil tablets are for oral administration.
Adults: Recommended Dose: 100 mg taken as needed approximately 1 hr before sexual activity for most patients. 
Based on effectiveness and toleration, the dose may be increased to a maximum recommended dose of 100 mg or decreased to 25 mg. The maximum recommended dose is 100 mg. The maximum recommended dosing frequency is once per day.
Patients with Impaired Renal Function: Dosage adjustments are not required in patients with mild to moderate renal impairment (creatinine clearance 30-80 mL/min).
Since sildenafil clearance is reduced in patients with severe renal impairment (creatinine clearance <30 mL/min), a 25-mg dose should be considered.
Patients with Impaired Hepatic Function: Since sildenafil clearance is reduced in patients with hepatic impairment (eg, cirrhosis), a 25-mg dose should be considered.
Patients Using Other Medications: Given the extent of the interaction with patients receiving concomitant therapy with ritonavir (see Interactions), it is recommended not to exceed a maximum single dose of sildenafil 25 mg in a 48-hr period.
A starting dose of 25 mg should be considered in patients receiving concomitant treatment with the CYP3A4 inhibitors (eg, erythromycin, saquinavir, ketoconazole, itraconazole). (See Interactions.)
In order to minimize the potential for developing postural hypotension, patients should be stable on α-blocker therapy prior to initiating sildenafil treatment. In addition, initiation of sildenafil at lower doses should be considered (see Precautions and Interactions).
Elderly: Dosage adjustments are not required in elderly patients.

Overdosage

 

In studies with healthy volunteers of single doses up to 800 mg, adverse events were similar to those seen at lower doses but incidence rates and severities were increased.
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.

 

 

Administration

May be taken with or without food.

 

Contraindications

Patients with a known hypersensitivity to any component of Viagra.
Sildenafil was shown to potentiate the hypotensive effects of acute and chronic nitrates, and its administration to patients who are concurrently using NO donors, organic nitrates or organic nitrites in any form either regularly or intermittently is therefore contraindicated (see Interactions).

 

Warnings

 

Sildenafil citrate is not an aphrodisiac.
Administration to patients with cardiac disease who are currently using nitrates is contraindicated because of possible fatal outcome.
Use of sildenafil is contraindicated in children, women and patients with hepatic and renal dysfunction.
Viagra must not be taken more than once a day.
Concomitant administration with other anti-impotent drugs is contraindicated.
Immediate consultation to physicians is recommended, should the following symptoms occur eg, abnormal vision, bone pain, chest pain, tachycardia, perspiration and collapse from exhaustion.

 

Special Precautions

Special Precautions

A thorough medical history and physical examination should be undertaken to diagnose erectile dysfunction, determine potential underlying causes and identify appropriate treatment.
There is a degree of cardiac risk associated with sexual activity; therefore, physicians may wish to consider the cardiovascular status of their patients prior to initiating any treatment for erectile dysfunction.
Agents for the treatment of erectile dysfunction should not be used in men for whom sexual activity is inadvisable (eg, patients with severe cardiovascular disorders eg, unstable angina or severe cardiac failure).
Serious cardiovascular events, including myocardial infarction, sudden cardiac death, ventricular arrhythmia, cerebrovascular hemorrhage and transient ischemic attack have been reported post-marketing in temporal association with the use of sildenafil for erectile dysfunction. Most, but not all, of these patients had preexisting cardiovascular risk factors. Many of these events were reported to occur during or shortly after sexual activity, and a few were reported to occur shortly after the use of sildenafil without sexual activity. Others were reported to have occurred hours to days after the use of sildenafil and sexual activity. It is not possible to determine whether these events are related directly to sildenafil, sexual activity, patient's underlying cardiovascular disease, a combination of these factors or other factors.
In clinical trials, sildenafil has been shown to have systemic vasodilatory properties that result in transient decreases in blood pressure (see Pharmacodynamics: Clinical Studies under Pharmacology under Actions). This is of little or no consequence in most patients. However, prior to prescribing sildenafil, physicians should carefully consider whether their patients with certain underlying conditions could be adversely affected by such vasodilatory effects, especially in combination with sexual activity. Patients with increased susceptibility to vasodilators include those with left ventricular outflow obstruction (eg, aortic stenosis, hypertrophic obstructive cardiomyopathy) or those with the rare syndrome of multiple system atrophy manifesting as severely impaired autonomic control of blood pressure.
Non-arteritic anterior ischemic optic neuropathy (NAION), a cause of decreased vision or loss of vision, has been reported rarely post-marketing with the use of all PDE5 inhibitors, including sildenafil. Most of these patients had risk factors eg, low cup to disc ratio ("crowded disc"), age >50, diabetes, hypertension, coronary artery disease, hyperlipidemia and smoking. No causal relationship has been made between use of PDE5 inhibitors and NAION. Physicians should discuss with patients the increased risk of NAION in individuals who have already experienced NAION. The patients should be advised that, in case of sudden visual loss, to stop taking sildenafil and consult a physician immediately.
Caution is advised when sildenafil is administered to patients taking an α-blocker, as the co-administration may lead to symptomatic hypotension in susceptible individuals (see Interactions). In order to minimize the potential for developing postural hypotension, patients should be hemodynamically stable on α-blocker therapy prior to initiating sildenafil treatment. Initiation of sildenafil at lower doses should be considered (see Dosage & Administration). In addition, physicians should advise the patients what to do in the event of postural hypotensive symptoms.
A minority of patients with the inherited condition retinitis pigmentosa have genetic disorders of retinal phosphodiesterases. There is no safety information on the administration of sildenafil to patients with retinitis pigmentosa, therefore, sildenafil should be administered with caution to these patients.
Agents for the treatment of erectile dysfunction should be used with caution in patients with anatomical deformation of the penis (eg, angulation, cavernosal fibrosis or Peyronie's disease) or in patients who have conditions which may predispose them to priapism (eg, sickle-cell anemia, multiple myeloma or leukemia).
In vitro studies with human platelets indicate that sildenafil potentiates the antiaggregatory effect of sodium nitroprusside (an NO donor). There is no safety information on the administration of sildenafil to patients with bleeding disorders or active peptic ulceration, therefore, sildenafil should be administered with caution to these patients.
Agents for the treatment of erectile dysfunction should be used with caution in patients with anatomical deformation of the penis (eg, angulation, cavernosal fibrosis or Peyronie's disease) or in patients who have conditions which may predispose them to priapism (eg, sickle cell anemia, multiple myeloma or leukemia).
The safety and efficacy of combinations of sildenafil with other treatments for erectile dysfunction have not been studied and the use of such combinations is not recommended.
Sudden decrease or loss of hearing has been reported in a small number of post-marketing and clinical trial cases with the use of all PDE5 inhibitors, including sildenafil. Most of these patients had risk factors for sudden decrease or loss of hearing. No causal relationship has been made between the use of PDE5 inhibitors and sudden decrease or loss of hearing. In case of sudden decrease or loss of hearing, patients should be advised to stop taking sildenafil and consult a physician promptly.
Effects on the Ability to Drive or Operate Machinery: The effect of sildenafil on the ability to drive and use machinery has not been studied.

 

.

Use In Pregnancy & Lactation

 

Sildenafil is not indicated for use in women.
No teratogenic effects, impairment of fertility or adverse effects on peri/postnatal development were found in reproduction studies in rats and rabbits following oral administration of sildenafil.
There are no adequate and well-controlled studies in pregnant or lactating women

 

Use in Children: Sildenafil is not indicated for use in children (<18 years).

 

Side Effects / Adverse Reactions

Transient & mild to moderate headache, flushing, dizziness, abnormal vision/photosensitive or blurred vision, chromatopsia, palpitation, nasal congestion, dyspepsia. 
Adverse Reactions

The adverse events were generally transient and mild to moderate in nature. 
In fixed-dose studies, the incidence of some adverse events increased with dose.
The nature of the adverse events in flexible-dose studies, which more closely reflect the recommended dosage regimen, was similar to that for fixed-dose studies.
The most commonly reported adverse reactions were headache and flushing (see table).



At doses above the recommended dose range, adverse events were similar to those detailed previously but generally were reported more frequently.
In an analysis of double-blind, placebo-controlled clinical trials encompassing over 700 person-years of observation on placebo and over 1300 person-years on sildenafil, there were no differences in the incidence rate of MI or in the rate of cardiovascular mortality for patients receiving sildenafil compared to those receiving placebo. The rates of MI were 1.1 per 100 person-years for men receiving sildenafil and for those receiving placebo. The rates of cardiovascular mortality were 0.3 per 100 person-years for men receiving sildenafil and those receiving placebo.
The following adverse reactions were reported during post-marketing surveillance:
Immune System Disorders: Hypersensitivity reaction (including skin rash).
Nervous System Disorders: Seizure, seizure recurrence.
Cardiovascular Disorders: Serious cardiovascular events, including myocardial infarction, angina pectoris intermediate syndrome, sudden cardiac death, ventricular arrhythmia, cerebrovascular haemorrhage, transient ischemic attack, hypertension, hypotension, syncope, tachycardia, palpitation and epistaxis have been reported post-marketing in temporal association with the use of Viagra.
Vascular Disorders: Hypotension, syncope, epistaxis.
Gastrointestinal Disorders: Vomiting.
Eye Disorders: Eye pain, red eyes/bloodshot eyes.
Reproductive System and Breast Disorders: Prolonged erection and/or priapism.

 

Interactions

Ketoconazole, erythromycin, cimetidine, ritonavir, doxazosin. Potentiate the hypotensive effect of acute & chronic nitrates.

 Category B: Either animal-reproduction studies have not demonstrated a foetal risk but there are no controlled studies in pregnant women or animal-reproduction studies have shown an adverse effect (other than a decrease in fertility) that was not confirmed in controlled studies in women in the 1^sttrimester (and there is no evidence of a risk in later trimesters).

 

Description

Viagra also contains the following excipients: Microcrystalline cellulose, anhydrous calcium hydrogen phosphate, croscarmellose sodium, magnesium stearate, hydroxypropyl methylcellulose (hypromellose), titanium dioxide (E171), lactose, triacetin and FD&C blue #2 aluminum lake [indigo carmine aluminum lake (E132)].

 

Presentation / Packing

100 mg (blue, rounded diamond-shaped, marked "PFIZER" on one side and "VGR 100" on the other) x 4's.

 

Storage

Store below 30°C.

 

 

Mechanism of Action

Pharmacology: Pharmacodynamics: Sildenafil, 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).
Mechanism of Action: The physiologic mechanism of erection of the penis involves release of nitric oxide (NO) in the corpus cavernosum during sexual stimulation.
Nitric oxide then activates the enzyme guanylate cyclase, which results in increased levels of 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 NO by inhibiting PDE5 which is responsible for the 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.
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 and PDE4, PDE7-PDE11).
The approximately 4000-fold selectivity for PDE5 versus PDE3 is important because PDE3 is involved in control of cardiac contractility.
Clinical Studies: Cardiac: Single oral doses of sildenafil up to 100 mg produced no clinically relevant changes in the ECGs of normal male volunteers. 
The mean maximum decreases in supine systolic blood pressure following 100-mg oral dosing was 8.3 mmHg. The corresponding change in supine diastolic blood pressure was 5.3 mmHg. 
Larger but similarly transient effects on blood pressure were recorded among patients receiving concomitant nitrates (see Contraindications and Interactions).
In a study of the hemodynamic effects of a single oral 100-mg dose of sildenafil in 14 patients with severe coronary artery disease (CAD) (>70% stenosis of at least 1 coronary artery), the mean resting systolic and diastolic blood pressures decreased by 7% and 6%, respectively, compared to baseline. Mean pulmonary systolic blood pressure decreased by 9%. Sildenafil showed no effect on cardiac output and did not impair blood flow through the stenosed coronary arteries, and resulted in improvement (approximately 13%) in adenosine-induced coronary flow reserve (in both stenosed and reference arteries).
In a double-blind, placebo-controlled trial, 144 patients with erectile dysfunction and stable angina, who were taking their regular antianginal medications (except nitrates) were exercised until limiting angina occurred. The duration of treadmill exercise was statistically significantly longer (19.9 sec; 95% confidence interval: 0.9-38.9 sec) in the evaluable patients who had taken a single dose of sildenafil 100 mg compared to patients who had taken a single dose of placebo. The mean exercise times (adjusted for baseline) to onset of limiting angina were 423.6 and 403.7 sec for sildenafil and placebo, respectively.
A randomized, double-blind, placebo-controlled, flexible-dose study (sildenafil up to 100 mg) in males (N=568) with erectile dysfunction and arterial hypertension taking ≥2 antihypertensive agents was conducted. Sildenafil improved the erections in 71% of men compared to 18% in the placebo group, and 62% of attempts at sexual intercourse were successful with sildenafil compared to 26% on placebo. The incidence of adverse events was consistent with observations in other patient populations, as well as in the subjects taking ≥3 antihypertensive agents.
Visual: Mild and transient differences in color discrimination (blue/green) were detected in some subjects using the Farnsworth-Munsell 100 hue test at 60 min following a 100-mg dose, with no effects evident after 120 min post-dose. The postulated mechanism for this change in color discrimination is related to inhibition of PDE6, which is involved in the phototransduction cascade of the retina. In vitro studies show that sildenafil is 10-fold less potent against PDE6 than PDE5. Sildenafil has no effect on visual acuity, contrast sensitivity, electroretinograms, intraocular pressure or pupillometry.
In a placebo-controlled, crossover study of patients with documented early age-related macular degeneration (n=9), sildenafil (single dose, 100 mg) was well tolerated and demonstrated no clinically significant changes in the visual tests conducted (visual acuity, Amsler grid, color discrimination, simulated traffic light, Humphrey perimeter and photostress).
Efficacy: The efficacy and safety of sildenafil was evaluated in 21 randomized, double-blind, placebo-controlled trials of up to 6 months duration. Sildenafil was administered to >3000 patients 19-87 years, with erectile dysfunction of various etiologies (organic, psychogenic, mixed). The efficacy was evaluated by global assessment question, diary of erections, the International Index of Erectile Function (IIEF, a validated sexual function questionnaire) and a partner questionnaire.
Sildenafil efficacy, determined as the ability to achieve and maintain an erection sufficient for sexual intercourse, was demonstrated in all 21 studies and was maintained in long-term extension studies (1 year). In fixed-dose studies, the proportions of patients reporting that treatment improved their erections were 62% (25 mg), 74% (50 mg) and 82% (100 mg) compared to 25% on placebo. In addition to improvements in erectile dysfunction, analysis of the IIEF showed that sildenafil treatment also improved the domains of orgasm, satisfaction with intercourse and overall satisfaction.
Across all trials, the proportions of patients reporting improvement on sildenafil were 59% of diabetic patients, 43% of radical prostatectomy patients and 83% of patients with spinal cord injury (vs 16%, 15% and 12% on placebo, respectively).
Pharmacokinetics: Sildenafil pharmacokinetics are dose-proportional over the recommended dose range.
It is eliminated predominantly by hepatic metabolism [mainly cytochrome P-450 (CYP) 3A4] and is converted to an active metabolite with properties similar to the parent, sildenafil.
Absorption: Sildenafil is rapidly absorbed after oral administration, with mean absolute bioavailability of 41% (range 25-63%).
Sildenafil inhibits the human PDE5 enzyme in vitro by 50% at a concentration of 3.5 nM. In man, the mean maximum free plasma concentration of sildenafil following a single oral dose of 100 mg is approximately 18 ng/mL or 38 nM.
Maximum observed plasma concentrations are reached within 30-120 min (median 60 min) of oral dosing in the fasted state.
When sildenafil is taken with a high-fat meal, the rate of absorption is reduced with a mean delay in T_max of 60 min and a mean reduction in C_max of 29%. However, the extent of absorption was not significantly affected (AUC decreased by 11%).
Distribution: The mean steady-state volume of distribution (V_ss) 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.
Based upon measurements of sildenafil in semen of healthy volunteers 90 min after dosing, <0.0002% (average 188 ng) of the administered dose may appear in the semen of patients.
Metabolism: Sildenafil is cleared predominantly by the CYP3A4 (major route) and CYP2C9 (minor route) hepatic microsomal isoenzymes.
The major circulating metabolite results from N-desmethylation of sildenafil, and is itself further metabolized.
This metabolite has a PDE selectivity profile similar to sildenafil and an in vitro potency for PDE5 approximately 50% of the parent drug.
In healthy volunteers, plasma concentrations of this metabolite are approximately 40% of those seen for sildenafil.
The N-desmethyl metabolite is further metabolized, with a terminal half-life of approximately 4 hrs.
Elimination: The total body clearance of sildenafil is 41 L/hr with a resultant terminal phase half-life of 3-5 hrs. After either oral or IV administration, sildenafil is excreted as metabolites predominantly in the feces (approximately 80% of administered oral dose) and to a lesser extent in the urine (approximately 13% of administered oral dose).
Pharmacokinetics in Special Patient Groups: Elderly: Healthy elderly volunteers (≥65 years) had a reduced clearance of sildenafil, resulting in approximately 90% higher plasma concentrations of sildenafil and the active N-desmethyl metabolite compared to those seen in healthy younger volunteers (18-45 years). Due to age-differences in plasma protein-binding, the corresponding increase in free sildenafil plasma concentration was approximately 40%.
Renal Insufficiency: In volunteers with mild (creatinine clearance 50-80 mL/min) and moderate (creatinine clearance 30-49 mL/min) renal impairment, the pharmacokinetics of a single oral dose of sildenafil (100 mg) were not altered. 
In volunteers with severe (creatinine clearance <30 mL/min) renal impairment, sildenafil clearance was reduced, resulting in approximately doubling of AUC (100%) and C_max (88%) compared to age-matched volunteers with no renal impairment (see Dosage & Administration).
In addition, N-desmethyl metabolite AUC and C_max values were significantly increased 200% and 79%, respectively in subjects with severe renal impairment compared to subjects with normal renal function.
Hepatic Insufficiency: In volunteers with hepatic cirrhosis (Child-Pugh A and B), sildenafil clearance was reduced, resulting in increases in AUC (84%) and C_max (47%) compared to age-matched volunteers with no hepatic impairment (see Dosage & Administration). The pharmacokinetics of sildenafil in patients with severely impaired hepatic function (Child-Pugh class C) have not been studied.
Toxicology: Preclinical Safety Data: No evidence of drug-related carcinogenicity was revealed in a 24-month study in rats at doses up to 42 times the maximum recommended human dose (MRHD) on a mg/kg basis and approximately 5 times the MRHD on a mg/m² bases and in an 18-21 month study in mice at doses up to 21 times the MRHD on a mg/kg basis (approximately 2 times the MRHD on a mg/m² basis).
Bacterial and in vivo mutagenicity tests were negative.
There was no effect on sperm motility or morphology after single 100-mg oral doses of sildenafil in healthy volunteers.

 

ATC Classification

G04BE03 - sildenafil ; Belongs to the class of drugs used in erectile dysfunction.