Product Information
Registration Status: ActiveVIAGRA TABLET 25mg is approved to be sold in Singapore with effective from 1999-03-17. It is marketed by PFIZER PTE LTD, with the registration number of SIN10804P.
This product contains Sildenafil 25mg in the form of TABLET, FILM-COATED. It is approved for ORAL use.
This product is manufactured by Pfizer PGM in FRANCE.
It is a Prescription Only Medicine that can only be obtained from a doctor or a dentist, or a pharmacist with a prescription from a Singapore-registered doctor or dentist.
Description
Sildenafil is a vasoactive agent used to treat erectile dysfunction and reduce symptoms in patients with pulmonary arterial hypertension (PAH). Sildenafil elevates levels of the second messenger, cGMP, by inhibiting its breakdown via phosphodiesterase type 5 (PDE5). PDE5 is found in particularly high concentrations in the corpus cavernosum, erectile tissue of the penis. It is also found in the retina and vascular endothelium. Increased cGMP results in vasodilation which facilitates generation and maintenance of an erection. The vasodilatory effects of sildenafil also help reduce symptoms of PAH.
Indication
For the treatment of erectile dysfunction and to relieve symptoms of pulmonary arterial hypertension (PAH).
Mechanism of Action
Sildenafil inhibits the cGMP-specific phosphodiesterase type 5 (PDE5) which is responsible for degradation of cGMP in the corpus cavernosum located around the penis. Penile erection during sexual stimulation is caused by increased penile blood flow resulting from the relaxation of penile arteries and corpus cavernosal smooth muscle. This response is mediated by the release of nitric oxide (NO) from nerve terminals and endothelial cells, which stimulates the synthesis of cGMP in smooth muscle cells. Cyclic GMP causes smooth muscle relaxation and increased blood flow into the corpus cavernosum. The inhibition of phosphodiesterase type 5 (PDE5) by sildenafil enhances erectile function by increasing the amount of cGMP.
Pharmacokinetics
- Absorption
- >90% absorbed with ~40% reaching systemic circulation unchanged following first-pass metabolism
- Distribution
- * 105 L
- Metabolism
- Sildenafil appears to be completely metabolized in the liver to 16 metabolites. Its metabolism is mediated mainly by cytochrome P450 microsomal isozymes 3A4 (major route) and 2C9 (minor route). The major circulating metabolite, N-demethylated metabolite, has PDE selectivity similar to the parent drug and ~50% of its in vitro potency. The N-demethylated metabolite is further metabolized to an N-dealkylated N,N-de-ethylated metabolite. Sildenafil also undergoes N-dealkylation followed by N-demethylation of the piperazine ring.
- Elimination
Active Ingredient/Synonyms
1-((3-(4,7-Dihydro-1-methyl-7-oxo-3-propyl-1H-pyrazolo(4,3-d)pyrimidin-5-yl)-4-ethoxyphenyl)sulfonyl)-4-methylpiperazine | Sildenafil |
Source of information: Drugbank (External Link). Last updated on: 3rd July 18. *Trade Name used in the content below may not be the same as the HSA-registered product.