Viagra is rapidly absorbed. Maximum observed plasma concentrations are reached within 30 to minutes median 60 minutes of oral dosing in the fasted state. The mean steady state volume of distribution Vss for sildenafil is L, indicating distribution into the tissues.
Protein binding is independent of total drug concentrations. Based upon measurements of sildenafil in semen of healthy volunteers 90 minutes after dosing, less than 0. The major circulating metabolite results from N-desmethylation of sildenafil, and is itself further metabolized. Similar values for pharmacokinetic parameters were seen in normal volunteers and in the patient population, using a population pharmacokinetic approach. Pharmacokinetics in Special Populations Geriatrics: The pharmacokinetics of sildenafil in patients with severely impaired hepatic function Child-Pugh Class C have not been studied [see Dosage and Administration 2.
A starting oral dose of 25 mg should be considered in those patients [see Dosage and Administration 2. Therefore, inhibitors of these isoenzymes may reduce sildenafil clearance and inducers of these isoenzymes may increase sildenafil clearance. The concomitant use of erythromycin or strong CYP3A4 inhibitors e. Viagra had no effect on saquinavir pharmacokinetics. A stronger CYP3A4 inhibitor such as ketoconazole or itraconazole could be expected to have greater effect than that seen with saquinavir.
Population pharmacokinetic data from patients in clinical trials also indicated a reduction in sildenafil clearance when it was co-administered with CYP3A4 inhibitors such as ketoconazole, erythromycin, or cimetidine [see Dosage and Administration 2. This is consistent with ritonavir's marked effects on a broad range of P substrates. Viagra had no effect on ritonavir pharmacokinetics [see Dosage and Administration 2. Although the interaction between other protease inhibitors and sildenafil has not been studied, their concomitant use is expected to increase sildenafil levels.
In a study of healthy male volunteers, co-administration of sildenafil at steady state 80 mg t. Concomitant administration of strong CYP3A4 inducers, such as rifampin, is expected to cause greater decreases in plasma levels of sildenafil. In healthy male volunteers, there was no evidence of a clinically significant effect of azithromycin mg daily for 3 days on the systemic exposure of sildenafil or its major circulating metabolite.
Pharmacokinetic data from patients in clinical trials showed no effect on sildenafil pharmacokinetics of CYP2C9 inhibitors such as tolbutamide, warfarin , CYP2D6 inhibitors such as selective serotonin reuptake inhibitors, tricyclic antidepressants , thiazide and related diuretics, ACE inhibitors, and calcium channel blockers. These effects on the metabolite are not expected to be of clinical consequence. Effects of Viagra on Other Drugs In vitro studies: No significant interactions were shown with tolbutamide mg or warfarin 40 mg , both of which are metabolized by CYP2C9.
In a study of healthy male volunteers, sildenafil mg did not affect the steady state pharmacokinetics of the HIV protease inhibitors, saquinavir and ritonavir, both of which are CYP3A4 substrates. Viagra 50 mg did not potentiate the increase in bleeding time caused by aspirin mg.
Sildenafil at steady state, at a dose not approved for the treatment of erectile dysfunction 80 mg t. Nonclinical Toxicology Carcinogenesis, Mutagenesis, Impairment of Fertility Carcinogenesis Sildenafil was not carcinogenic when administered to rats for 24 months at a dose resulting in total systemic drug exposure AUCs for unbound sildenafil and its major metabolite of and times, for male and female rats, respectively, the exposures observed in human males given the Maximum Recommended Human Dose MRHD of mg.
Mutagenesis Sildenafil was negative in in vitro bacterial and Chinese hamster ovary cell assays to detect mutagenicity, and in vitro human lymphocytes and in vivo mouse micronucleus assays to detect clastogenicity. Clinical Studies In clinical studies, Viagra was assessed for its effect on the ability of men with erectile dysfunction ED to engage in sexual activity and in many cases specifically on the ability to achieve and maintain an erection sufficient for satisfactory sexual activity.
Viagra was evaluated primarily at doses of 25 mg, 50 mg and mg in 21 randomized, double-blind, placebo-controlled trials of up to 6 months in duration, using a variety of study designs fixed dose, titration, parallel, crossover. Viagra was administered to more than 3, patients aged 19 to 87 years, with ED of various etiologies organic, psychogenic, mixed with a mean duration of 5 years.
Viagra demonstrated statistically significant improvement compared to placebo in all 21 studies. The studies that established benefit demonstrated improvements in success rates for sexual intercourse compared with placebo. Efficacy Endpoints in Controlled Clinical Studies The effectiveness of Viagra was evaluated in most studies using several assessment instruments.
The primary measure in the principal studies was a sexual function questionnaire the International Index of Erectile Function - IIEF administered during a 4-week treatment-free run-in period, at baseline, at follow-up visits, and at the end of double-blind, placebo-controlled, at-home treatment. Two of the questions from the IIEF served as primary study endpoints; categorical responses were elicited to questions about 1 the ability to achieve erections sufficient for sexual intercourse and 2 the maintenance of erections after penetration.
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Sexual function data were also recorded by patients in a daily diary. One-third to one-half of the subjects in these studies reported successful intercourse at least once during a 4-week, treatment-free run-in period. 25mg effects on the metabolite are not expected to be of clinical consequence. Effects of Viagra on Sperm: In these studies, involving about patients, analyses of patient diaries showed no effect of Viagra on rates of attempted intercourse about 2 per weekbut there was clear treatment-related improvement in sexual function: I pass on the information and they are so happy to hear first-hand experience and that the process works from someone who has used it before. Figure 6 shows that regardless of the baseline levels sildenafil function, subsequent function in patients treated with Viagra was better than that seen in patients treated with placebo. As in the other titration studies, patients were started on 50 mg and allowed to adjust the dose up to mg or down to 25mg mg of Viagra; all patients, however, bula sildenafil 25mg, were receiving 50 mg or mg at the end of the study. Even though Blink does not need a copy of your prescription, you must have a valid prescription from the doctor to pick up at the pharmacy. The primary endpoint was time to limiting angina in the evaluable bula. In addition, patients bula asked a global efficacy question and an optional partner questionnaire was administered. Nonclinical Toxicology Carcinogenesis, Mutagenesis, Impairment of Fertility Carcinogenesis Sildenafil was not carcinogenic when administered to rats for 24 months at a dose resulting in total systemic drug exposure AUCs for unbound sildenafil and its major metabolite of and times, sildenafil male and female rats, respectively, the exposures observed in human males given the Maximum Recommended Human Dose MRHD of mg.
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