Instruction for Viagra Use

Viagra is a medication created for erectile dysfunction treatment.

Viagra Description

The active substance: Sildenafil Citrate
Administration: The drug is used to increase potency and is applied to erectile dysfunction treatment.
Viagra Pills: coated light blue, diamond-shaped, slightly convex pills with cut and round edges being released in 25, 50 and 100 pills. Its composition includes cellulose, magnesium stearate, calcium hydrogen phosphate anhydrous, croscarmellose sodium.

Dosage and Instruction for Use

For an oral intake 30 minutes before the sexual intercourse. The daily recommended dosage is 100 mg with a possible decrease or increase up to 50 and 25 mg respectively considering individual medication tolerance. The daily dose of 100 mg is prescribed for a daily intake.

Mechanism of Action

Viagra is proven and most convenient drug for ED treatment. This medication is a selective inhibitor of specific phosphodiesterase 5 (PDE5).

Sildenafil effect manifests itself with sexual stimulation only. It does not contribute to visual loss syndrome and has no effect on intraocular pressure, pupil size.

This ED drug has no direct relaxing effect on isolated corpus cavernouma, but enhances the relaxing effect of the nitric oxide – NO on this tissue by inhibiting PDE5, which is responsible for cGMP degradation in the cavernous body.

The influence of PDE5 inhibition by sildenafil results in increased cGMP levels in the cavernous body, resulting in smooth muscle relaxation and increased blood flow to the cavernous body.

In some patients, after 1 hour after drug administration at a dose of 100 mg using the Farnsworth-Munsell 100 showed mild and transient impaired ability to distinguish between color shades (blue/green); 2 hours after receiving these changes disappear.

It is believed that color vision violation is caused by the inhibition of PDE6, which is involved in light transmission in the retina. Viagra has no effect on visual acuity, contrast perception, electroretinogram, intraocular pressure and pupil diameter.

Pharmacokinetics

Pharmacokinetics depends on the dose – 25 mg to 100 mg per day.

Absorption into Blood

Sildenafil is rapidly absorbed. After taking 100 mg of sildenafil limiting drug concentration in the blood is 18 ng/ml (38nM). This drug taken on an empty stomach reaches its maximum within 30 minutes to 2 hours minimum.

At the use of fatty foods, sildenafil absorption in the blood increased by about 30 minutes, and the maximum concentration is reduced by 29%.

Distribution

Sildenafil and other drug components approximately in 96% of cases bind to plasma protein. Sildenafil concentration has no effect on protein binding. When receiving 100 mg of sildenafil, 0.0002% (average 188 ng) will be detected in sperm within 30 minutes after administration.

Metabolism

Basically, sildenafil is metabolized under the influence of CYP3A4 (major route) and CYP2C9 (minor route) – hepatic microsomal isoenzymes. The concentration of the metabolite in plasma is approximately 40% of that of sildenafil.

Indications

Viagra is prescribed for erectile dysfunction treatment. It is effective only if there is natural sexual stimulation.

Dosage

• The drug is taken orally.
• The usual initial dose is 50 mg for an hour before intercourse. If lack of efficacy and side effects are observed, the dosage can be increased to 100 mg or decreased to 25 mg.
• Take no more than 1 time per day.
• For elderly men dose adjustment is required.
• In severe renal insufficiency, the dose was reduced to 25 mg. In renal insufficiency, mild or moderate dose adjustment is necessary.
• In case of liver pathologies, dosage can be reduced to 25 mg.
• When combined with ritonavir, the maximum dose of sildenafil should be 25 mg, no more than 1 time in 48 hours.

In a joint application with inhibitors of CYP3A4 isoenzyme (such as erythromycin, saquinavir, ketoconazole, itraconazole), the initial dose should be 25 mg.

To minimize the risk of postural hypotension in patients taking alpha-blockers, they should start taking Sildenafil only after hemodynamic stabilization.

Side Effects

Side effects are usually considered mild.

The frequency of adverse events is increased with dose magnifying.

The most common side effects:

• Nervous system: headache (10.8%);
• Cardiovascular system: vasodilation (10.9%).

Common side effects:

• dizziness (2.9 %);
• blurred vision, changes in sensitivity to light (2.5%).

Digestive system:

• dyspepsia (3.0 %);
• chromatic vision (mild and transient, mostly change
  perception of color shades) (1.1 %);
• Cardiovascular palpitations (1.0 %);
• Respiratory rhinitis (nasal congestion) (2.1 %).

In case of overdose the following side effects are observed:

1. Immune System: hypersensitivity reactions (including rash).
2. Cardiovascular system: tachycardia, decreased blood pressure, fainting, nasal hemorrhage.
3. Digestive system: vomiting.
4. Bodies: eye pain, eye redness / scleral injection.
5. Reproductive system: prolonged erection and/or priapism.

Contraindications

The most common contraindications are:

• hypersensitivity and intolerance to drug components;
• medications of nitric oxide, nitrates in any form application.

You should not take Viagra if you suffer from the following diseases:

• anatomical penis deformity;
• cavernous fibrosis;
• angulation;
• Peyronie’s disease;
• drepanocytemia;
• multiple myeloma;
• leukosis;
• thrombocytopenia.

Other contraindications are:

• diseases accompanied with bleeding;
• aggravation of gastric and duodenal ulcer;
• retinitis pigmentosa;
• heart failure;
• unstable angina;
• previous myocardial infarction and blood stroke;
• severe arrhythmia;
• hypertension.