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LEVITRA (VARDENAFIL): PHARMACOKINETICS
The pharmacokinetics of Levitra (Vardenafil) tablets are approximately dose proportional over the recommended dose range. Vardenafil is eliminated predominantly by hepatic metabolism, mainly by CYP3A4 and to a minor extent, CYP2C isoforms. Concomitant use with potent CYP3A4 inhibitors such as ritonavir, indinavir, ketoconazole, as well as moderate CYP3A inhibitors such as erythromycin results in significant increases of plasma levels of vardenafil.
Vardenafil (Levitra) is rapidly absorbed with absolute bioavailability of approximately 15%. Maximum observed plasma concentrations after a single 20 mg dose in healthy volunteers are usually reached between 30 minutes and 2 hours (median 60 minutes) after oral dosing in the fasted state. Two food-effect studies were conducted which showed that high-fat meals caused a reduction in Cmax by 18%-50%.
The mean steady-state volume of distribution (Vss) for vardenafil is 208 L, indicating extensive tissue distribution. Vardenafil (Levitra) tablets and its major circulating metabolite, M1, are highly bound to plasma proteins (about 95% for parent drug and M1). This protein binding is reversible and independent of total drug concentrations.
Following a single oral dose of 20 mg vardenafil in healthy volunteers, a mean of 0.00018% of the administered dose was obtained in semen 1.5 hours after dosing.
Levitra (Vardenafil HCl) is metabolized predominantly by the hepatic enzyme CYP3A4, with contribution from the CYP3A5 and CYP2C isoforms. The major circulating metabolite, M1, results from desethylation at the piperazine moiety of vardenafil. M1 is subject to further metabolism. The plasma concentration of M1 is approximately 26% that of the parent compound. This metabolite shows a phosphodiesterase selectivity profile similar to that of vardenafil and an in vitro inhibitory potency for PDE5 28% of that of vardenafil. Therefore, M1 accounts for approximately 7% of total pharmacologic activity.
The total body clearance of Vardenafil Hydrochloride (Levitra) tablets is 56 L/h, and the terminal half-life of vardenafil and its primary metabolite (M1) is approximately 4-5 hours. After oral administration, vardenafil is excreted as metabolites predominantly in the feces (approximately 91-95% of administered oral dose) and to a lesser extent in the urine (approximately 2-6% of administered oral dose).
Pharmacokinetics in Special Populations
Levitra (Vardenafil HCl) tablets trials were not conducted in the pediatric population.
In a healthy volunteer study of elderly males ( >= 65 years) and younger males (18-45 years), mean Cmax and AUC were 34% and 52% higher, respectively, in the elderly males.
Consequently, a lower starting dose of Levitra 5 mg in patients >= 65 years of age should be considered.
In volunteers with mild renal impairment (CLcr = 50-80 ml/min), the pharmacokinetics of vardenafil were similar to those observed in a control group with normal renal function. In the moderate (CLcr = 30-50 ml/min) or severe (CLcr < 30 ml/min) renal impairment groups, the AUC of vardenafil was 20.30% higher compared to that observed in a control group with normal renal function (CLcr >80 ml/min). Vardenafil (Levitra) pharmacokinetics have not been evaluated in patients requiring renal dialysis.
In volunteers with mild hepatic impairment (Child-Pugh A), the Cmax and AUC following a 10 mg vardenafil dose were increased by 22% and 17%, respectively, compared to healthy control subjects. In volunteers with moderate hepatic impairment (Child-Pugh B), the Cmax and AUC following a 10 mg vardenafil dose were increased by 130% and 160%, respectively, compared to healthy control subjects. Consequently, a starting dose of 5 mg is recommended for patients with moderate hepatic impairment, and the maximum dose should not exceed 10 mg. Vardenafil (Levitra) tablets has not been evaluated in patients with severe (Child-Pugh C) hepatic impairment.
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