Sildenafil Citrate Pharmacology

Sildenafil Citrate

About Sildenafil Citrate
Phosphodiesterase-5 Enzyme Inhibitor, Anti-erectile dysfunction agent.
Mechanism of Action of Sildenafil Citrate
Sildenafil is a phosphodiesterase enzyme (PDE5) inhibitor. This enzyme is responsible for the degradation cyclic guanosine monophosphate (cGMP) produced in reaction to sexual stimulation. The more cGMP is available, the more durable the erection. Sildenafil inhibits the PDE5 enzyme, preserving cGMP levels, therefore aiding erection viability and durability
Erection of the penis is caused by the filling of the penis with blood. Filling occurs because the blood vessels that bring blood to the penis increase in size and deliver more blood to the penis and at the same time, the blood vessels that take blood away from the penis decrease in size and remove less blood from the penis.
Sexual stimulation that leads to an erection causes the production and release of nitric oxide in the corpora cavernosa of the penis. The nitric oxide causes an enzyme guanylate cyclase, to produce cyclic guanosine monophosphate (cGMP). It is the cGMP that is primarily responsible for increasing and decreasing the size of the blood vessels carrying blood to and from the penis, respectively, and causing the erection. When the cGMP is destroyed by enzyme phosphodiesterase-5, the blood vessels return to their normal size, blood leaves the penis, and the erection ends. Sildenafil prevents phosphodiesterase-5 from destroying cGMP so that cGMP stays around longer. The persistence of cGMP leads to a more prolonged engorgement of the penis with blood. It relaxes muscles and increases blood flow to particular areas of the body.
Pharmacokinets of Sildenafil Citrate
Absorption: It is readily absorbed from the bloodstream and the bioavailability is about 40%.
Distribution: It is widely distributed in protein bound form (96% bound to plasma protein) mostly to tissues.
Metabolism: It is metabolized in the liver by an enzyme known as CYP3A4 and others to produce active N-Desmethyl derivatives.
Excretion: It is primarily excreted in the feces (80%) and small amount in the urine
Onset of Action for Sildenafil Citrate
Within 30 minutes
Duration of Action for Sildenafil Citrate
4 hours
Half Life of Sildenafil Citrate
4 hours
Side Effects of Sildenafil Citrate
1. Facial flushing
2. Headaches
3. Stomach upset
4. Diarrhea
5. Flu-like symptoms
6. Nausea
7. Back pain
8. Muscle aches
9. Low blood pressure
10. Blurred vision
11. Abnormal ejaculation
12. Prolonged erections
13. Sweating
14. General ill feeling
15. Irregular heartbeat
16. Swelling in hands, ankles, or feet
17. Shortness of breath
18. Lightheadedness
19. Fainting

In pre-existing heart disease:
1. Chest pain
2. Heart attacks
3. Death
4. Strokes
5. Palpitations and increased heart rate
6. Vision changes

Contra-indications of Sildenafil Citrate
1. Hypersensitivity to Sildenafil
2. Patients on nitrate therapy
3. Patients taking a adrenergic receptor antagonist
Special Precautions while taking Sildenafil Citrate
1. Do not take Sildenafil more than once a day
2. Contact doctor if erection is painful or lasts longer than 4 hours
3. Heart disease
4. Recent history a heart attack (within the past 90 days)
5. Recent history of stroke or congestive heart failure (within the past 6 months)
6. Angina
7. Hypotension
8. Hypertension
9. Liver disease
10. Kidney disease
11. Sickle cell anemia
12. Multiple myeloma
13. Leukemia
14. Haemophilia
15. Stomach ulcer
16. Retinitis pigmentosa
17. Peyronie`s disease (physical deformity of the penis)
18. Diabetes
19. High cholesterol
20. Pre-existing eye problems
21. One who smoke or are over 50 years old
Pregnancy Related Information
Old Age Related Information
Use with caution
Breast Feeding Related Information
Children Related Information
NEONATES: Contraindicated
Indications for Sildenafil Citrate
1. Erectile dysfunction
Interactions for Sildenafil Citrate
Non-specific beta-blockers, loop and potassium-sparing diuretics enhance efficacy of sildenafil. Concomitant administration of sildenafil 100mg and amlodipine 5 or 10mg in hypertensive patients led to a mean additional blood pressure reduction of 8mm Hg systolic and 7mm Hg diastolic. Cytochrome P450 inhibitors like erythromycin, ketoconazole, itraconazole are likely to reduce sildenafil clearance.

Typical Dosage for Sildenafil Citrate
Adult: 50 mg taken, 1 hour before sexual activity or anywhere from 0.5 - 4 hours before sexual activity. Based on effectiveness and toleration, the dose may be increased to a maximum 100 mg or decreased to 25 mg. The maximum recommended dosing frequency is once per day.
Schedule of Sildenafil Citrate
Storage Requirements for Sildenafil Citrate
Store at room temperature between 15-30?C. Protect from moisture and heat. Keep out of the reach of children.
Effects of Missed Dosage of Sildenafil Citrate
Sildenafil is used as needed, not likely to be on a dosing schedule.
Effects of Overdose of Sildenafil Citrate
No overdose, if any overdose occurs then seeks immediate medical attention. Give supportive measures and symptomatic treatment.

Home Delivery for Sildenafil Citrate in Your City

Medicine India is just a publishing medium for medicine related information and does not provide services or sales of medicines including sildenafil citrate.

However, we do publish a comprehensive directory of Pharmacies, Chemists and Druggists in cities all over India. You can use this directory to find the medicine stores in your city (or area) that provide home delivery services for sildenafil citrate and other medicines and health products. Home delivery services for sildenafil citrate may be free or they may cost you depending on the pharmacy and the minimum order requirements. It would be best to get this clarified while placing the order.

Please be aware that you should take sildenafil citrate only if a doctor has recommended or prescribed it. Some or all pharmacies who provide a home delivery service for medicines might insist on a prescription for sildenafil citrate before they complete the sale. You can get this information while placing the order for sildenafil citrate with the pharmacy.

Sildenafil Citrate is a generic medicine name and there are several brands available for it. Some of the brands for sildenafil citrate might be better known than sildenafil citrate itself. If the pharmacy that's willing to deliver medicines to your home doesn't have sildenafil citrate in stock, you can ask for one of the branded alternatives for sildenafil citrate.