Viagra Tablets - Indications, Dosage, Presentation and How It Works

I am sure you have already heard about Viagra, it is a common medicine use to treat erectile dysfunction. If you are considering to use Viagra you should first read this post. In this post, I am going to tell you why Viagra is used or indicated, how much of viagra you should take / dosage, how to recognize original Viagra tablets means presentation of this drug, as well as how Viagra works and which company manufactures Viagra tablets.
Viagra tablets packing
VIAGRA 100 mg  boxed packing.

VIAGRA Tablets Indications:

VIAGRA is indicated in adult men with erectile dysfunction, which is the inability to achieve or maintain a penile erection sufficient for satisfactory sexual activity. Viagra is referred to men for the treatment of erectile dysfunction.

VIAGRA: its dosage  

Use in adults:

The recommended dose is 50 mg taken as needed approximately one hour before sexual activity. Depending on efficacy and tolerance, the dose may be increased to 100 mg or decreased to 25 mg. The maximum recommended dose is 100 mg. The maximum frequency of use is once per day.
If the drug is taken with food, the action of VIAGRA may be delayed compared to the fasted state (see section Pharmacokinetic properties ).

Elderly:

Patient should not take VIAGRA whose age is (≥ 65 years).

In Case of Renal failure/problems:

The dosing recommendations described in "Use in adults" apply to patients with mild to moderate renal impairment (creatinine clearance = 30-80 mL / min).
Sildenafil clearance is reduced in patients with severe renal impairment (creatinine clearance <30 mL / min), using a 25 mg dose should be considered. According to the efficacy and tolerability, the dose can be gradually increased to 50 mg and 100 mg if necessary.

Hepatic insufficiency:

Sildenafil clearance is reduced in patients with hepatic impairment (eg. Cirrhosis), the use of a dose of 25 mg should be considered. Depending on efficacy and tolerance, the dose can be gradually increased to 50 mg and up to 100 mg if necessary.

VIAGRA is not indicated for individuals below 18 years.

VIAGRA Presentation:

Blue colored, film coated, diamond-shaped tablets.  With the inscription of words "Pfizer" on one side and "VGR 100" on the other side. VIAGRA comes in many packing types but the tablets look same. VIAGRA comes in 50 mg and 100 mg or both.

How VIAGRA works:

Therapeutic category of VIAGRA: urological; drugs used in erectile dysfunction, ATC code: G04B E03.

Action mechanism:

Sildenafil is an oral therapy for erectile dysfunction. Under natural conditions, ie with sexual stimulation, it restores impaired erectile function by increasing blood flow to the penis.

The physiological mechanism responsible for the erection of the penis involves release of nitric oxide (NO) in the Corpus Cavernosum during sexual stimulation. The nitrogen oxide 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 is a potent and selective inhibitor of phosphodiesterase type 5 (PDE5), cGMP specific, in the corpus cavernosum; it is here that PDE5 is responsible for degradation of cGMP. Sildenafil has a peripheral site of action on erections. Sildenafil has no direct relaxant effect on the fabric of the isolated human corpus cavernosum but enhances significantly the relaxant effect of NO on this tissue. When the NO / cGMP pathway is activated, as during sexual stimulation, inhibition of PDE5 by Sildenafil causes increased levels of cGMP in the corpus cavernosum. Therefore sexual stimulation is needed for sildenafil to produce its beneficial pharmacological effects.

Pharmacodynamic effects

In vitro studies have shown that sildenafil is selective for PDE5, which is involved in the erectile process. Its effect is more potent on PDE5 than on other known phosphodiesterases. There is a 10-fold selectivity higher compared to PDE6, which is involved in the phototransduction pathway of the retina. At maximum recommended doses, there is a 80-fold selectivity over PDE1, and over 700-fold over PDE2, 3, 4, 7, 8, 9, 10 and 11. In particular, sildenafil is more of 4,000-fold selectivity for PDE5 over PDE3, isoform-specific phosphodiesterase cAMP involved in the control of cardiac contractility.

Clinical efficacy and safety

Two clinical studies were specifically designed to assess at what time after administration and for how long sildenafil could produce an erection in response to sexual stimulation.

In a study of penile plethysmography (RigiScan) in fasting patients taking sildenafil, the median time to obtain an erection sufficient for sexual intercourse (60% rigidity) was 25 minutes (range: 12 to 37 minutes ).

In another study with RigiScan, sildenafil could still induce an erection in response to sexual stimulation 4-5 hours after administration.

Sildenafil results in mild and transient decreases in blood pressure which, in most cases, do not translate into clinical effects.

The mean maximal decrease in systolic blood pressure supine after oral administration of 100 mg of sildenafil was 8.4 mmHg.

The corresponding change in diastolic blood pressure in the supine position was 5.5 mmHg. These decreases in blood pressure are consistent with the vasodilatory effects of sildenafil, probably due to increased cGMP levels in vascular smooth muscle.

Single oral doses of sildenafil up to 100 mg in healthy volunteers did not give rise to any clinically relevant effects on ECG.

In a study of the hemodynamic effects of a single oral dose of 100 mg sildenafil in 14 patients with severe coronary artery disease (> 70% stenosis of at least one coronary artery), the mean systolic and diastolic blood pressure at rest decreased respectively 7% and 6% compared to the baseline. Mean pulmonary systolic blood pressure decreased by 9%.

Sildenafil showed no effect on cardiac output or no decrease in blood flow through stenosed coronary arteries have been highlighted.

A test double-blind placebo-controlled trial, evaluated 144 patients with erectile dysfunction and chronic stable angina and regularly taking anti-anginal treatment (except nitrates) subjected to a test of effort.

No clinically significant differences were observed between sildenafil and placebo on the time to onset of angina crisis.

Light and transient differences in the differentiation of colors (blue and green) were detected in some subjects using the Farnsworth-Munsell 100 test assessing distinguish shades one hour after administration of a dose of 100 mg; two hours after administration, no effect was observed.

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.

Sildenafil has no effect on visual acuity or contrast sensitivity.

In a placebo-controlled study in a small number of patients with a documented form of early macular degeneration (n = 9), sildenafil (single dose, 100 mg) demonstrated no significant changes in visual tests conducted (visual acuity, Amsler grid, color discrimination simulated traffic light, Humphrey perimeter and photostress).

No effect on motility or sperm morphology appeared only after the oral administration of a single dose of 100 mg of sildenafil in healthy volunteers (see section Pregnancy and lactation ).

Further information on clinical trials:

In clinical studies, sildenafil was administered to over 8000 patients aged 19 to 87 years.

The following patient groups were represented: elderly (19.9%), patients with hypertension (30.9%), diabetes mellitus (20.3%), ischemic heart disease (5.8%), d hyperlipidemia (19.8%), a lesion of the spinal cord (0.6%), depression (5.2%), transurethral resection of the prostate (3.7%) of radical prostatectomy (3.3%).

However, the following groups were not represented or excluded from clinical trials: patients who underwent surgery in the pelvis or radiotherapy, patients with severe renal or hepatic impairment and patients with certain cardiovascular conditions (see Contraindications ).

In fixed dose studies, the proportion of patients reporting improved erections with treatment was 62% (25 mg), 74% (50 mg) and 82% (100 mg) against 25% in patients receiving placebo.

In clinical studies, the rate of discontinuation due to sildenafil was low and similar to placebo.

In all trials, the proportion of patients taking sildenafil reporting improvement was (by population) 84% (erectile dysfunction psychogenic), 77% (mixed erectile dysfunction), 68% (organic erectile dysfunction), 67% (elderly ), 59% (diabetes mellitus), 69% (ischemic heart disease), 68% (hypertensive), 61% (transurethral resection of the prostate), 43% (radical prostatectomy), 83% (of the spinal cord injury) and 75 % (depression). The safety and efficacy of sildenafil was maintained in long term studies.

Pediatric population

The European Medicines Agency has waived the obligation to submit the results of studies with VIAGRA in all subsets of the pediatric population for the treatment of erectile dysfunction.

Producing Company

Pfizer Inc.
 
The blue diamond tablet shape is a registered trademark of Pfizer Inc.

VIAGRA (sildenafil citrate), REVATIO (sildenafil), Cardura (doxazosin mesylate), and Minipress (prazosin HCl) are registered trademarks of Pfizer Inc.

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