Viagra is a drug that is given to men with certain sexual problems in order to help them to have sex. The safety of Viagra is unknown in patients with bleeding disorders and patients with active peptic ulceration.
An oral therapy for erectile dysfunction, is the citrate salt of sildenafil, a selective inhibitor of cyclic guanosine monophosphate. The inhibition Pharmacodynamics in these tissues by sildenafil may be the basis for the enhanced platelet antiaggregatory activity of nitric oxide observed. It is rapidly absorbed after oral administration, with a mean absolute bioavailability of 41% such as the range 25 to 63%.
Viagra pharmacokinetics
Its pharmacokinetics is dose-proportional over the recommended dose range. After either oral or intravenous administration, sildenafil is excreted as metabolites predominantly in the feces and to a lesser extent in the urine. Similar values for pharmacokinetic parameters were seen in normal volunteers and in the patient population, using a population pharmacokinetic approach. In eight double blind, placebo controlled crossover studies of patients with either organic or psychogenic erectile dysfunction, sexual stimulation resulted in improved erections, as assessed by an objective measurement of hardness and duration of erections. Most studies assessed the efficacy of Viagra approximately 60 minutes post dose. The time course of effect was examined in one study, showing an effect for up to 4 hours but the response was diminished compared to 2 hours.
It contains the diastolic blood pressures decreased by 7% and 10% compared to baseline in these patients. Mean resting values for right artery pressure, pulmonary artery pressure, pulmonary artery occluded pressure and cardiac output decreased by 28%, 28%, 20% and 7% respectively. Even though this total dosage produced plasma sildenafil concentrations which were approximately 2 to 5 times higher than the mean maximum plasma concentrations following a single oral dose of 100 mg in healthy male volunteers, the hemodynamic response to exercise was preserved in these patients.
At single oral doses of 100 mg and 200 mg, transient dose-related impairment of color discrimination (blue/green) was detected using the Farnsworth-Munsell 100-hue test, with peak effects near the time of peak plasma levels. The effectiveness of Viagra was evaluated in most studies using several assessment instruments. The primary measure in the principal studies was a sexual function questionnaire administered during a 4 week treatment-free run-in period. The effect on one of the major end points, maintenance of erections after penetration for the pooled results of 5 fixed doses, dose response studies of greater than one month duration, showing response according to baseline function.
Results with all doses have been pooled, but scores showed greater improvement at the 50 and 100 mg doses than at 25 mg. The pattern of responses was similar for the other principal question, the ability to achieve an erection sufficient for intercourse. The titration studies, in which most patients received 100 mg and across all trials, Viagra improved the erections of 43% of radical prostatectomy patients compared to 15% on placebo.
There is a potential for cardiac risk of sexual activity in patients with preexisting cardiovascular disease. Therefore, treatments for erectile dysfunction, including Viagra, should not be generally used in men for whom sexual activity is inadvisable because of their underlying cardiovascular status.
Viagra should be used with caution in patients with anatomical deformation of the penis such as angulation, cavernosal fibrosis or Peyronieâs disease, or in patients who have conditions which may predispose them to priapism such as sickle cell anemia, multiple myeloma, or leukemia.
Medical Practitioner (General Practice) with postgraduate diplomas in Cape Town. My special interest is erectile dysfunction.