Viagra is indicated in adult men with erectile dysfunction, which is the inability to obtain or maintain an erection sufficient for satisfactory sexual activity for both sides and prevent “sagging”. For Viagra be effective, sexual stimulation is required.
Mechanism of Action
Sildenafil in the presence of sexual stimulation, it restores impaired erectile function by increasing blood flow to the penis. The physiological mechanism responsible for erection of the penis involves the release of nitric oxide (NO) in the corpus cavernosum during sexual stimulation. Nitric oxide activates guanylate cyclase, resulting in an increase in cGMP levels producing a relaxation of smooth muscle in the corpora cavernosa of the penis. Sildenafil is a potent and selective inhibitor of phosphodiesterase 5 (PDE5), specific enzyme of the corpora cavernosa responsible for degradation of cGMP. Sildenafil has no direct relaxant effect on isolated human corpus cavernosum but enhances the relaxant effect of NO on this tissue.
Dosage
• Adults Oral: 50 mg (range 25-100 mg, depending on tolerability and efficacy) taken as needed, about an hour before intercourse.
• Elderly, severe renal impairment, mild or moderate hepatic impairment initial dose 25 mg, which can be increased to 50-100 mg, according to efficacy and tolerance.
• Standards for the correct administration: Take once a day, an hour before intercourse. Food delays the onset of action.
Contraindications
Hypersensitivity to the active substance or to any of the excipients. According to its known effects via nitric oxide / cyclic guanosine monophosphate (cGMP) sildenafil was shown to potentiate the hypotensive effects of nitrates, concomitant administration of sildenafil being contraindicated with nitric oxide donors (such as amyl nitrite) or nitrate in any form. Co-administration of PDE5 inhibitors, including sildenafil, with stimulators, as riociguat guanylate cyclase, it is contraindicated since it may lead to symptomatic hypotension potential form.
Special warnings and precautions for use
It is recommended that a medical history and physical examination of the patient, to diagnose erectile dysfunction and determine potential underlying causes, before pharmacological treatment is considered.
Cardiovascular risk factors
Before initiating any treatment for erectile dysfunction, physicians should consider the cardiovascular status of their patients, since there is a cardiac risk associated with sexual activity. Sildenafil has vasodilator properties, resulting in mild and transient decreases in blood pressure. Before prescribing sildenafil, physicians should carefully consider whether their patients with certain underlying conditions could be adversely affected by such, especially in combination with sexual activity vasodilatory effects. Patients with increased susceptibility to vasodilators include those with obstruction of the left ventricular outflow tract (eg aortic stenosis, hypertrophic obstructive cardiomyopathy), or those with the rare syndrome of multiple system atrophy is characterized by severely impaired autonomic control pressure blood.
Priapism
Drugs for the treatment of erectile dysfunction, including sildenafil, should be used with caution in patients with anatomical deformation of the penis (such as angulation, cavernous fibrosis or Peyronie’s disease), or in patients with conditions that may predispose them to priapism (such as sickle cell anemia, multiple myeloma or leukemia).
Effects on vision
Spontaneously, there have been reports of visual defects in association with the intake of sildenafil and other PDE5 inhibitors. Spontaneously and in an observational study, there have been reports of non-arteritic anterior ischemic optic neuropathy, a rare disease in association with the intake of sildenafil and other PDE5 inhibitors. Patients should be advised that in case of any sudden visual defect, stop taking Viagra and consult a physician immediately.
Adverse effects
Adverse reactions are generally mild and transient and dose dependent. It has been reported the following adverse reactions with an incidence> 1%:
– Cardiovascular: headache (12.8%), flushing, hot flushes (10.4%), dizziness (1.2%).
– Dermatologic / Allergic: rash (2%) eruptions.
– Digestive: dyspepsia (4.6%; 12% 100 mg), diarrhea (3%).
– Genitourinary: urinary tract infections (3%).
– Otorhinolaryngologic: nasal congestion (4%).
– Ocular: visual disturbances (1.9%; 11% at doses of 100 mg), mild and transient, predominantly abnormal color perception, increased perception of light or blurred vision, reversible change in the electroretinogram (volunteers, dose 100 mg).
– Sex: priapism. Additionally muscle pain was observed when administered more frequently than the recommended. The dropout rate due to adverse events was similar with sildenafil and placebo (around 2%).
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Hello, welcome. I am Peter Doherty, Australian physician from Melbourne. My goal is to provide you important information about Viagra and its substitutes.