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Sildenafil citrate.

VIAGRA 50 mg: Each tablet contains sildenafil citrate equivalent to 50 mg sildenafil.
VIAGRA 100 mg: Each tablet contains sildenafil citrate equivalent to 100 mg sildenafil.
For excipients, see as follows. Buy Viagra online, for sale in Australia
Excipients/Inactive Ingredients: In addition to the active ingredient, sildenafil citrate, each tablet contains the following inactive ingredients: microcrystalline cellulose, calcium hydrogen phosphate (anhydrous), croscarmellose sodium, magnesium stearate, hydroxypropyl methylcellulose (hypromellose), titanium dioxide (E171), lactose, triacetin, and FD & C Blue #2 aluminum lake (indigo carmine aluminium lake [E132]).

Pharmacology: Pharmacodynamics: Sildenafil, an oral therapy for erectile dysfunction, is the citrate salt of sildenafil, a selective inhibitor of cyclic guanosine monophosphate (cGMP)-specific phosphodiesterase type 5 (PDE5).
Mechanism of Action: The physiologic mechanism of erection of the penis involves release of nitric oxide (NO) in the corpus cavernosum during sexual stimulation. Buy Viagra online, for sale in Australia
NO then activates the enzyme guanylate cyclase, which results in increased levels of cyclic guanosine monophosphate (cGMP), producing smooth muscle relaxation in the corpus cavernosum and allowing inflow of blood.
Sildenafil has no direct relaxant effect on isolated human corpus cavernosum, but enhances the effect of NO by inhibiting of phosphodiesterase type 5 (PDE5), which is responsible for degradation of cGMP in the corpus cavernosum.
When sexual stimulation causes local release of NO, inhibition of PDE5 by sildenafil causes increased levels of cGMP in the corpus cavernosum, resulting in smooth muscle relaxation and inflow of blood to the corpus cavernosum.
Sildenafil at recommended doses has no effect in the absence of sexual stimulation.
Studies in vitro have shown that sildenafil is selective for PDE5. Buy Viagra online, for sale in Australia
Its effect is more potent on PDE5 than on other known phosphodiesterases (10-fold for PDE6, >80-fold for PDE1, >700-fold for PDE2, PDE3, and PDE4, PDE7 – PDE11).
The approximately 4,000-fold selectivity for PDE5 versus PDE3 is important because PDE3 is involved in the control of cardiac contractility.
Clinical studies: Cardiac: Single oral doses of sildenafil up to 100 mg produced no clinically relevant changes in the ECGs of normal male volunteers.Pharmacokinetics: Sildenafil pharmacokinetics are dose-proportional over the recommended dose range.
It is eliminated predominantly by hepatic metabolism (mainly cytochrome P450 3A4) and is converted to an active metabolite with properties similar to the parent, sildenafil. Buy Viagra online, for sale in Australia
Absorption: Sildenafil is rapidly absorbed after oral administration, with mean absolute bioavailability of 41% (range 25%-63%).
Sildenafil inhibits the human PDE5 enzyme in vitro by 50% at a concentration of 3.5 nM. In man, the mean maximum free plasma concentration of sildenafil following a single oral dose of 100 mg is approximately 18 ng/mL, or 38 nM. Buy Viagra online, for sale in Australia
Maximum observed plasma concentrations are reached within 30 to 120 minutes (median 60 minutes) of oral dosing in the fasted state.
When sildenafil film-coated tablets are taken with a high fat meal, the rate of absorption of sildenafil is reduced, with a mean delay in T_max of 60 minutes and a mean reduction in C_max of 29%, however, the extent of absorption was not significantly affected (AUC decreased by 11%).
Distribution: The mean steady-state volume of distribution (V_ss) for sildenafil is 105 L, indicating distribution into the tissues. Buy Viagra online, for sale in Australia
Sildenafil and its major circulating N-desmethyl metabolite are both approximately 96% bound to plasma proteins.
Protein binding is independent of total drug concentrations.
Based upon measurements of sildenafil in semen of healthy volunteers 90 minutes after dosing, less than 0.0002% (average 188 ng) of the administered dose may appear in the semen of patients. Buy Viagra online, for sale in Australia
Metabolism: Sildenafil is cleared predominantly by the CYP3A4 (major route) and CYP2C9 (minor route) hepatic microsomal isoenzymes.
The major circulating metabolite results from N-desmethylation of sildenafil, and is itself further metabolized.
This metabolite has a PDE selectivity profile similar to sildenafil and an in vitro potency for PDE5 approximately 50% of the parent drug.