Viagra Dosage: How to take Viagra
Generic name: Sildenafil Citrate.
Dosage: Viagra 25mg, 50mg, 100mg, 150mg, 120mg, 200mg.
Category: Men’s Health.
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How to take Viagra
For most patients, the recommended dose is 50 mg; the medication should be taken as needed approximately 1 hour before sexual activity. Depending on effectiveness and tolerability, the dose may be increased to 100 mg or decreased to 25 mg.
After oral administration, sildenafil is rapidly absorbed. The maximum plasma concentration of sildenafil (Cmax) is achieved within 30–120 minutes (average 60 minutes) after oral administration on an empty stomach. The average absolute bioavailability after oral administration of the drug is 40%. Following oral administration of sildenafil in the recommended dose range (25–100 mg), the area under the pharmacokinetic curve (AUC) and Cmax values increase in direct proportion to the dose taken.
When sildenafil is taken with food, the rate of absorption is reduced with an average delay in time to maximum plasma concentration (tmax) of 60 minutes and an average decrease in Cmax of 30%.
After oral administration of sildenafil in a single dose of 100 mg, the average maximum total plasma concentration of sildenafil is approximately 440 ng/ml (with a coefficient of variation of 40%). Due to the fact that sildenafil is 96% bound to plasma proteins, the average maximum concentration of free sildenafil in blood plasma is 18 ng/ml (38 nM). Protein binding is independent of the total drug concentration.
In healthy volunteers who received a single dose of sildenafil 100 mg, less than 0.0002% of the dose was found in the ejaculate 90 minutes after taking the dose.
The terminal half-life of Sildenafil is 3 to 5 hours.
Viagra dosage
For oral use. Viagra can be taken regardless of meals. However, if you take Viagra with food, the pill may take longer to work.
The recommended dose of Viagra is 50 mg orally approximately 1 hour before sexual intercourse. Considering the effectiveness and tolerability, the dose can be increased to 100 mg. The maximum recommended dose is 100 mg.
The tablet must be swallowed whole with a glass of water. The maximum recommended frequency of use is 1 time per day.
In elderly patients (≥ 65 years), no dose adjustment is required. For mild to moderate renal failure (creatinine clearance 30–80 ml/min), no dose adjustment is required. Due to the fact that the clearance of sildenafil is reduced in patients with impaired liver function (for example, cirrhosis), the use of the drug at a dose of 25 mg should be considered. Considering the effectiveness and tolerability of the drug, if necessary, its dose can be gradually increased to 50 mg and 100 mg.
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Side Effects
- Nervous System: Headache
- Cardiovascular System: Vasodilation (flushing)
- Visual System: Changes in vision (blurred vision, sensitivity to light) Chromatopsia (mild and transient, mainly altering color perception)
- Respiratory System: Rhinitis (nasal congestion)
- Digestive System: Dyspepsia
- General state disturbances: reactions of increased sensitivity (including skin rash)
- Changes in the central and peripheral nervous systems: seizures
- Changes in the cardiovascular system: tachycardia, low blood pressure, fainting, nosebleeds
- Gastrointestinal disorders: vomiting Changes in the visual system: eye pain, redness of the eyes/conjunctival injection
- Reproductive system disorders: prolonged erection and/or priapism.
Overdose
With a single dose of the drug up to 800 mg, adverse events were comparable to those with sildenafil at lower doses but occurred more frequently. Treatment: symptomatic therapy. Hemodialysis does not accelerate sildenafil clearance because it is actively bound to plasma proteins and not excreted in the urine.
Interaction with other drugs
Impact of other medications on sildenafil metabolism Sildenafil metabolism mainly occurs in the liver under the action of CYP3A4 (the main pathway) and CYP2C9 isoenzymes, so inhibitors of these isoenzymes may decrease sildenafil clearance, while inducers may increase sildenafil clearance. When combined with CYP3A4 inhibitors (such as ketoconazole, erythromycin, cimetidine), a decrease in sildenafil clearance has been noted. Cimetidine (at a dose of 800 mg), a non-specific CYP3A4 inhibitor, when taken concomitantly with sildenafil (at a dose of 50 mg), increases sildenafil plasma concentration by 56%. A single dose of sildenafil 100 mg simultaneously with erythromycin – a specific CYP3A4 inhibitor (when erythromycin is taken at 500 mg twice daily for 5 days) – with steady-state erythromycin blood concentration leads to a 182% increase in sildenafil AUC. When sildenafil (at a single dose of 100 mg) is administered simultaneously with saquinavir (at a dose of 1200 mg three times daily), which is both an HIV protease inhibitor and a CYP3A4 inhibitor, with steady-state saquinavir blood concentration, sildenafil Cmax in the blood increased by 140%, and AUC increased by 210%. Sildenafil did not affect the pharmacokinetic parameters of saquinavir. Stronger CYP3A4 isoenzyme inhibitors such as ketoconazole or itraconazole may cause more pronounced changes in sildenafil pharmacokinetics. Simultaneous administration of sildenafil (at a single dose of 100 mg) and ritonavir (500 mg twice daily), an HIV protease inhibitor and a strong inhibitor of cytochrome P450 isoenzymes, with steady-state ritonavir blood concentration leads to a 300% increase in sildenafil Cmax (4-fold) and a 1000% increase in AUC (11-fold). After 24 hours, sildenafil plasma concentration was approximately 200 ng/ml (after a single sildenafil administration – 5 ng/ml). If sildenafil is taken at recommended doses by patients receiving strong CYP3A4 inhibitors, the Cmax of free sildenafil does not exceed 200 nM, and the drug is well tolerated. A single dose of antacid (magnesium hydroxide/aluminum hydroxide) does not affect sildenafil bioavailability. In studies involving healthy volunteers, simultaneous administration of the endothelin receptor antagonist bosentan (an inducer of CYP3A4 (moderate), CYP2C9, and possibly CYP2C19 isoenzymes) at steady-state concentration (125 mg twice daily) and sildenafil at steady-state concentration (80 mg three times daily) resulted in a 62.6% decrease in sildenafil AUC and a 52.4% decrease in Cmax. Sildenafil increased bosentan AUC and Cmax by 49.8% and 42%, respectively. It is assumed that simultaneous administration of sildenafil with potent CYP3A4 inducers such as rifampicin may lead to a greater decrease in sildenafil plasma concentration. CYP2C9 isoenzyme inhibitors (such as tolbutamide, warfarin), CYP2D6 isoenzyme inhibitors (such as selective serotonin reuptake inhibitors, tricyclic antidepressants), thiazides and thiazide-like diuretics, ACE inhibitors, and calcium antagonists do not affect sildenafil pharmacokinetics.
