22/12/2024
VI**RA®
(sildenafil citrate)
Tablets
DESCRIPTION
VI**RA®, 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).
Sildenafil citrate is designated chemically as 1-[[3-(6,7-dihydro-1-methyl-7-oxo-3-propyl-1Hpyrazolo[4,3-d]pyrimidin-5-yl)-4-ethoxyphenyl]sulfonyl]-4-methylpiperazine citrate and has the
following structural formula:
Sildenafil citrate is a white to off-white crystalline powder with a solubility of 3.5 mg/mL in
water and a molecular weight of 666.7. VI**RA (sildenafil citrate) is formulated as blue,
film-coated rounded-diamond-shaped tablets equivalent to 25 mg, 50 mg and 100 mg of
sildenafil for oral administration. In addition to the active ingredient, sildenafil citrate, each
tablet contains the following inactive ingredients: microcrystalline cellulose, anhydrous dibasic
calcium phosphate, croscarmellose sodium, magnesium stearate, hypromellose, titanium dioxide,
lactose, triacetin, and FD & C Blue #2 aluminum lake.
CLINICAL PHARMACOLOGY
Mechanism of Action
The physiologic mechanism of er****on of the p***s involves release of nitric oxide (NO) in the
corpus cavernosum during sexual stimulation. 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 nitric
oxide (NO) by inhibiting 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
