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Viagra Clinical Pharmacology |
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How Viagra works?
The penis gets erect during sexual stimulation when increased blood flows to the penis resulting from relaxation of penile arteries and corpus cavernosal smooth muscle. This is due to the release of nitric oxide (NO) from nerve terminals and endothelial cells which in turn leads to the synthesis of cGMP in smooth muscle cells.
Cyclic GMP (cGMP) causes muscle in the penis to relax so that more blood can flow in. Viagra is a selective inhibitor of PDE5. It inhibits the action of phosphodiesterase type 5 (PDE5) found in Corpus cavernosum smooth muscles in the penis. It is more effective for PDE5 than for other phosphodiesterases. Inhibition of PDE5 leads to an increases in the amount of cGMP.
Viagra Drug Interaction
Absorption :
Sildenafil citrate , the active ingredient in Viagra, is rapidly absorbed after oral administration . After single oral-dose administration, Sildenafil citrate achieves the maximum observed plasma concentration (C max ) between 30 minutes to 120 minutes (median time 60 minutes). When Sildenafil citrate is taken with a high fat meal, the rate of absorption is reduced.
Distribution :
Sildenafil citrate easily gets distributed into
tissues to the extent of 105 L. At therapeutic concentrations,
96% of Sildenafil citrate in plasma is bound to proteins.
Samples collected from healthy human subjects approximately
90 minutes after dosing indicated that less than 0.001%
of the total dose of Sildenafil citrate is distributed to
semen.
Pharmacodynamics
Effects on Blood Pressure
Single oral doses of sildenafil (100 mg) administered to healthy volunteers produced decreases in supine blood pressure (mean maximum decrease of 8.4/5.5 mmHg). The decrease in blood pressure was most notable approximately 1-2 hours after dosing, and was not different than placebo at 8 hours. Similar effects on blood pressure were noted with 25 mg, 50 mg and 100 mg of sildenafil citrate, therefore the effects are not related to dose or plasma levels. Larger effects were recorded among patients receiving concomitant nitrates.
Effects on vision-
Sildenafil can lead to blurred vision, changes in colour vision and inability to discriminate between green and blue colour.
Read about Viagra Safety
The health information contained herein is provided for educational purposes only and is not intended to replace discussions with a healthcare provider. Decisions regarding patient care must be made with a healthcare provider, considering the unique characteristics of the patient.
