Active Ingredient: Sildenafil citrate
Just like Viagra, Sildenafil (generic Viagra) used for treatment for erectile dysfunction, when a man is unable to get or maintain an erection, and is a very common condition which will affect most men in U.S. at some point in their lives. Sildenafil relaxes muscles and increases blood flow to particular areas of the body. The effect of the drug is symptomatic, it is aimed at more active work of the organs of the genital sphere, which are responsible for the development of an additional volume of the male sex hormone - testosterone, as well as filling the penile cavernous bodies with blood.
Description
Consider the composition of Generic Viagra and its action. The drug does not treat sexual disorders, but is intended solely for symptomatic therapy. During sexual intercourse with Viagra, the composition of its active ingredients ensures that the vessels of the penis are filled with a sufficient volume of blood. Due to this, a man receives an adequate response of the sexual organ to sexual arousal, as well as the opportunity to have a full sexual intercourse with a partner.
Side Effects
Headache, flushing, respiratory tract infection, angina pectoris, AV block, migraine, syncope, tachycardia, postural hypotension, MI, cerebral thrombosis, cardiac arrest, paraesthesia, tremor, depression, herpes simplex, skin ulcer, oesophagitis, abnormal LFT, rectal haemorrhage, hypoglycaemic reaction, arthritis, deafness, retinal vascular disease, photosensitivity, accidental fall.
Special Precautions
Caution when used in patients with anatomical deformation of penis or conditions that may predispose them to priapism (e.g. sickle cell anaemia, myeloma, or leukaemia). Mild, transient, dose-related impairment of colour discrimination (blue/green) may occur. Hepatic or severe renal impairment, bleeding disorders, active peptic ulceration, hypotension, recent history of stroke, MI, arrhythmias, unstable angina, heart failure or retinal disorders. May cause sudden loss or decrease in hearing. Overdosage: Should be managed by standard supportive care.
Dosage
Dose selection should be cautious, usually starting at the lower end of the dosing range, reflecting the greater frequency of decreased hepatic and renal function and comorbidity. Consider initial dose of 25 mg in patients older than 65 years of age.
Erectile dysfunction
Adult: 50 mg about 1 hour before sexual intercourse.
May adjust dose depending on penile response. Max: 100 mg/dose and not to be taken once in 24 hours.
Elderly: 65 years: Lower initial dose at 25 mg.
Hepatic impairment: Initially, 25 mg
The manufacturers of Viagra recommend taking Viagra one hour before having sex. However, studies have suggested that it could start working even sooner than that. Some men were able to achieve an erection just 12 minutes after taking Viagra, although this wasn't conclusively proven to be due to Viagra. And while the maximum concentration of sildenafil in the blood isn't reached until about an hour after taking it (and is potentially delayed by an additional hour if taken with food), it took a median of 27 minutes (with a range of 12–70 minutes) for men taking sildenafil to begin experiencing erections. This was 23 minutes sooner than the median time of 50 minutes experienced by those who took a placebo.
Pharmacokinetics
Sildenafil inhibits phosphodiesterase type-5 (PDE5) which is responsible for cGMP degradation in the corpus cavernosum. Inhibition of PDE5 increases cGMP levels in the corpus cavernosum which results in smooth muscle relaxation and inflow of blood to the corpus cavernosum.
Absorption: Rapidly absorbed after oral admin. Bioavailability: about 40%.
Distribution: Widely distributed. Plasma protein binding: 96%.
Metabolism: Metabolised in the liver mainly by CYP3A4 and CYP2C9.
Excretion: Excreted as metabolites mainly in the faeces.
The half-life of Viagra in the body is about four hours, meaning that every four hours after taking it, there's only half as much of the drug left. However, even 10 to 12 hours after taking Viagra, men could still often achieve erections hard enough for penetration, though of a shorter duration. By 24 hours, all traces of Viagra in the blood are practically gone.
Pregnancy
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 1st trimester (and there is no evidence of a risk in later trimesters).
Interactions
Inhibitors of CYP3A4 such as cimetidine and erythromycin are likely to reduce sildenafil clearance. CYP3A4 inducers such as rifampicin may decrease the plasma concentrations of sildenafil. Plasma concentrations are increased by ritonavir. Concurrent admin with grapefruit juice may lead to increased plasma levels of sildenafil. Potentially Fatal: May potentiate hypotensive effects of of organic nitrates and nicorandil.