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Instruction for Viagra

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Viagra is a remedy for the treatment of erectile dysfunction.

Release form and composition

Tablets in a blue film shell, biconvex diamond-shaped with cut rounded edges and Pfizer engraving on one side (in cardboard boxes with first opening control: 1 or 2 blisters, 1 or 2 tablets; 1 or 3 blisters, 4 tablets; 1 blister - 12 tablets).
The main active ingredient is sildenafil (in the form of citrate), its content corresponds to the engraving on the second side of the tablet and is in tablets with the inscription:
    VGR 25 - 25 mg;
    VGR 50 - 50 mg;
    VGR 100 - 100 mg.
Excipients in Viagra: microcrystalline cellulose, calcium hydrogen phosphate, croscarmellose sodium, magnesium stearate.
The composition of the film shell includes: hypromellose, lactose, triacetin, titanium dioxide (E171), aluminum varnish based on indigo carmine (E132), vanillin, biotin.

Pharmacodynamics

The active ingredient in Viagra - sildenafil - is an effective selective inhibitor of cycloguanosine monophosphate (cGMP) -specific phosphodiesterase type 5 (PDE5). This compound affects the physiological mechanism of erection in men by releasing nitric oxide in the corpus cavernosum during sexual stimulation. This causes an increase in the level of cGMP, further relaxation of the smooth muscle tissue of the corpus cavernosum and an intensification of blood flow.
Sildenafil is not characterized by a direct relaxing effect on the isolated corpus cavernosum in male patients, but this substance enhances the effect of nitric oxide due to inhibition of PDE5, which is responsible for the destruction of cGMP.
Sildenafil is distinguished by its selective action towards PDE5 in vitro, and its activity towards this compound is significantly higher than towards other known phosphodiesterase isoenzymes: in the case of PDE6 - 10 times, in the case of PDE1 - more than 80 times, and in the case of PDE7 – PDE11, PDE4, PDE2 - more than 700 times. The selectivity of the active component of Viagra in relation to PDE5 is 4000 times higher than that for PDE3. This is of great importance, since PDE3 is one of the key enzymes that regulate myocardial contractility.
Viagra has established itself as an effective drug only when used in combination with sexual stimulation. During its implementation, sildenafil normalizes impaired erectile function, increasing blood flow to the corpora cavernosa of the penis.
The active substance of the drug does not affect cardiac output and does not lead to impaired blood flow in stenotic coronary arteries, and also increases adenosine-induced coronary flow by approximately 13% in both intact and stenotic coronary arteries.
Sildenafil has no significant effect on electroretinogram, visual acuity, pupil diameter, intraocular pressure, or contrast perception.

Pharmacokinetics

When taking Viagra at the recommended dosage, the pharmacokinetics of sildenafil is linear. After oral administration, the substance is absorbed quickly enough. On average, its absolute bioavailability is approximately 40% with a spread range of 25–63%. If the in vitro concentration of sildenafil is approximately 1.7 ng / ml, this reduces human PDE5 activity by 50%.
With a single dose of Viagra at a dose of 100 mg, the average maximum concentration of free sildenafil in the blood plasma of male patients is 18 ng / ml. The maximum level of the substance when the drug is taken orally on an empty stomach is recorded on average after about 60 minutes (the likely time interval is 30-120 minutes). When Viagra is taken simultaneously with fatty foods, the absorption rate decreases: the maximum concentration of sildenafil decreases by about 29%, and the time to reach it increases by 60 minutes, however, the change in the degree of absorption is not confirmed by clinical data.
The volume of distribution of the active substance of the drug in an equilibrium state is approximately 105 liters. Sildenafil and its main circulating in the blood N-demethyl metabolite bind to blood plasma proteins by about 96%, and this is not affected by the total concentration of the drug in the body. Less than 0.0002% of the concentration of this compound (about 188 ng) was detected in semen 1.5 hours after taking Viagra.
Sildenafil is metabolized mainly in the liver under the action of the cytochrome CYP3A4 isoenzyme (main pathway) and the cytochrome CYP2C9 isoenzyme (minor pathway). This compound undergoes N-demethylation, resulting in the formation of the main circulating active metabolite, which is also further metabolized. This metabolite is characterized by practically the same selectivity of action with respect to PDE as sildenafil, and its activity with respect to PDE5 in vitro does not exceed 50% of the corresponding activity of sildenafil. The half-life of the N-demethyl metabolite is approximately 4 hours.
The total clearance of sildenafil reaches 41 l / h, and the final half-life is 3-5 hours. With both oral and intravenous administration, the substance is excreted as metabolites, predominantly through the intestine (approximately 80% of the oral dose) and to a lesser extent through the kidneys (approximately 13% of the oral dose).
In healthy elderly patients (over 65 years of age), the clearance of sildenafil decreases, and its plasma content is approximately 40% higher than in patients aged 18 to 45 years. No clinically significant effect of age on the incidence of side effects was found.
With renal failure mild (CC 50-80 ml / min) and moderate (CC 30-49 ml / min) severity, there are no changes in the pharmacokinetics of sildenafil after a single oral dose of Viagra at a dose of 50 mg. Severe renal failure (CC less than 30 ml / min) causes a decrease in the clearance of this substance, which leads to an increase in its maximum concentration in blood plasma by 88% compared with a similar indicator with normal renal function in patients of the same age group.
A decrease in sildenafil clearance is also observed in patients with liver cirrhosis (classes A and B in accordance with the Child-Pugh scale), which causes an increase in the maximum concentration of this substance by 47% compared with a similar indicator with normal liver function in patients of the same age group. The pharmacokinetics of sildenafil in patients with severe liver dysfunction (class C according to the Child-Pugh scale) has not been studied.

Indications for use

Therapy for erectile dysfunction, which is characterized by an inability to achieve or maintain an erection of the penis, which is necessary for a full intercourse.

Contraindications

    Combined treatment with other drugs intended for the treatment of erectile dysfunction;
    Continuous or occasional intake of nitric oxide donors, organic nitrites or nitrates in any form, since sildenafil enhances the hypotensive effect of nitrates;
    Female;
    Age under 18;
    Hypersensitivity to sildenafil or drug excipients.

Carefully

    Anatomical deformity of the penis, including angulation, cavernous fibrosis, or Peyronie's disease;
    Sickle cell anemia, multiple myeloma, thrombocytopenia, leukemia and other diseases that can cause the development of priapism;
    Diseases accompanied by bleeding, including in the case of exacerbation of gastric ulcer and duodenal ulcer;
    Hereditary retinitis pigmentosa.
It is recommended to use the drug under medical supervision during the first 6 months after a myocardial infarction or stroke, as well as for patients with heart diseases such as: heart failure, severe arrhythmias, arterial hypertension and / or hypotension, unstable angina pectoris.

Instructions for the use of Viagra: method and dosage

Viagra tablets are taken orally one hour before intercourse.
The initial dose is 50 mg. Depending on the effectiveness and individual tolerance, it can be corrected upward or downward.
The maximum dose of the drug per day should not exceed 100 mg, and the frequency of administration is 1 time.
For patients with severe renal failure or liver cirrhosis, the recommended dose is no more than 25 mg.
No dose adjustment is required for elderly patients.
If simultaneous treatment with other drugs is necessary, Viagra should be taken at 25 mg: with ritonavir - no more than 1 time every 48 hours; with erythromycin, ketoconazole, saquinavir, itraconazole - once a day.
To minimize the risk of postural hypotension in patients taking α-blockers, the drug should be started only after hemodynamic stabilization has been achieved. Consideration should also be given to reducing the starting dose of sildenafil.

Side effects

The degree of side effects depends on the individual tolerance of sildenafil, the side effects are transient:
    From the side of the central nervous system: most often - headache; often - dizziness; in some cases - convulsions;
    From the side of the cardiovascular system: most often - flushing of the face; often - rapid heartbeat; in some cases - tachycardia, decreased blood pressure, epistaxis, fainting;
    From the side of the organ of vision: often - impaired photosensitivity, blurred vision, transient chromatopsia; in some cases - eye pain, tearing, redness of the eyes;
    From the digestive system: often - dyspepsia, sometimes - vomiting;
    From the respiratory system: often - rhinitis;
    From the reproductive system: prolonged erection, priapism;
    Allergic reactions: skin rash, cough, runny nose.
Exceeding the recommended dosage causes similar side effects, only much more often.

Overdose

A single dose of sildenafil in doses not exceeding 800 mg can cause undesirable effects comparable to those when taking the drug at lower doses, but they are more common.
As a treatment, symptomatic therapy is prescribed. Hemodialysis does not intensify the clearance of sildenafil, since the compound actively binds to plasma proteins and is not excreted in the urine.

Special instructions

Viagra is prescribed by the attending physician based on a complete medical history and physical examination to determine the causes of erectile dysfunction.
Sexual activity is associated with a risk for men with cardiac pathologies, therefore, treatment to restore an erection should be carried out taking into account the recommendations of a cardiologist.
When taking the drug for hypotension, it should be borne in mind that sildenafil has a systemic vasodilating effect, which leads to a transient decrease in blood pressure. For most patients, it is not clinically significant and does not lead to serious consequences. Nevertheless, it is important that the doctor carefully evaluates the possible risk of undesirable manifestations of the vasodilating effect of the drug individually for each man, especially against the background of sexual activity. Patients with obstruction of the left ventricular outflow tract (hypertrophic obstructive cardiomyopathy, aortic stenosis), multiple systemic atrophy syndrome are susceptible to increased susceptibility to vasodilators.
When prescribing Viagra, the doctor should warn the patient about the significant risk of developing anterior non-arteritis ischemic neuropathy of the optic nerve, if this condition has already been noted in a man.
It is recommended to use Viagra with caution in patients with anatomical deformity of the penis.
The combined use of sildenafil and alpha-blockers can lead to symptomatic hypotension. Patients taking alpha-blockers are advised to start using Viagra only after hemodynamic stabilization, using the minimum dose. The physician should inform the patient of what action to take if symptoms of postural hypotension occur.
In case of hearing loss or loss during therapy, you should stop taking the drug and consult your doctor.
Since the safety and efficacy of using sildenafil in conjunction with other drugs for the treatment of erectile dysfunction has not been studied, it is not recommended to use such combinations.
According to the instructions, Viagra should not be prescribed to patients for whom sexual activity is undesirable.
At the beginning of treatment or in the case of dosage adjustments, you should be attentive to your well-being and be careful when driving.

Influence on the ability to drive vehicles and complex mechanisms

While taking Viagra, there is no negative effect of its active component on the ability to drive vehicles or other technical means.
However, sildenafil therapy can cause chromatopsia, blurred vision, low blood pressure, dizziness, and other side effects. Therefore, care must be taken when driving or performing potentially hazardous types of work that require increased concentration and immediate psychomotor reactions. You should also take into account the individual sensitivity to the drug in the above situations, especially when changing the dosage regimen or at the beginning of treatment.

Application during pregnancy and lactation

Viagra tablets are not recommended for use in women.

With impaired renal function

In case of mild to moderate renal failure (CC 30–80 ml / min), dose adjustment is not necessary, severe renal failure (CC less than 30 ml / min) is an indication for reducing the dose of sildenafil to 25 mg.

For violations of liver function

In patients with impaired liver function (for example, with cirrhosis), the excretion of sildenafil is impaired, so the dose of the drug is reduced to 25 mg.

Drug interactions

In the case of the simultaneous use of other drugs, it is necessary to take into account their possible mutual influence.
Sildenafil metabolism occurs in the liver, therefore, the clearance of sildenafil is directly dependent on drugs that affect the isoenzymes CYP3A4 and CYP2C9.
Concomitant use of ketoconazole, cimetidine, erythromycin and other CYP3A4 inhibitors reduces the clearance of sildenafil.
Viagra is well tolerated with strong CYP3A4 inhibitors, provided that it is taken in the recommended doses.
The pharmacokinetics of sildenafil are not influenced by: tolbutamide, warfarin and other inhibitors of the CYP2C9 isoenzyme; angiotensin-converting enzyme inhibitors; tricyclic antidepressants; selective serotonin reuptake inhibitors; thiazides and thiazide-like diuretics; calcium antagonists; azithromycin; combined antacids.
Sildenafil at a dose of 50 mg does not cause an additional increase in bleeding time when taking acetylsalicylic acid at a dose of 150 mg.
You can not take Viagra at the same time as nitrates or nitric oxide donors, as sildenafil enhances their hypotensive effect.
The simultaneous use of antihypertensive drugs does not cause side effects.
At the recommended dose (50 mg), sildenafil does not enhance the hypotensive effect of ethanol.

Terms and conditions of storage

Store in a dry place at a temperature not exceeding 30 ° C. Keep out of the reach of children.
The shelf life is 5 years.

Reviews about Viagra

According to reviews, Viagra has proven itself well in the treatment of erectile dysfunctions in men, which are the result of health problems, age or psycho-emotional stress. When used in accordance with the instructions, the drug acts well and quickly. Since it is available in different dosages (25, 50 and 100 mg), it simplifies the selection of the dosage regimen in each case.
The use of Viagra allows healthy men who have no problems with potency to feel new emotions. However, the drug should be used only after consulting a doctor in order to exclude complications during admission associated with diseases of the cardiovascular system.

Terms of sell

A prescription is not required to buy Viagra.