11 DESCRIPTION
Effect of Sildenafil Tablets and Placebo on Maintenance of Erection by Baseline Score.
3. Dosage Forms and Strengths
In addition, in a study performed in healthy male volunteers, co-administration of the HIV protease inhibitor saquinavir, also a CYP3A4 inhibitor, at steady state (1200 mg tid) with sildenafil tablets (100 mg single dose) resulted in a 140% increase in sildenafil Cmax and a 210% increase in sildenafil AUC. 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 (2.4)and Drug Interactions ( 7.4)]. In another study in healthy male volunteers, co-administration with the HIV protease inhibitor ritonavir, which is a highly potent P450 inhibitor, at steady state (500 mg bid) with sildenafil tablets (100 mg single dose) resulted in a 300% (4-fold) increase in sildenafil C maxand a 1000% (11-fold) increase in sildenafil plasma AUC. Sildenafil tablets had no effect on ritonavir pharmacokinetics [see Dosage and Administration (2.4)and Drug Interactions (7.4)]. Although the interaction between other protease inhibitors and sildenafil has not been studied, their concomitant use is expected to increase sildenafil levels.
How should I store sildenafil?
In a study of healthy male volunteers, co-administration of sildenafil at steady state (80 mg t.i.d.) with endothelin receptor antagonist bosentan (a moderate inducer of CYP3A4, CYP2C9 and possibly of CYP2C19) at steady state (125 mg b.i.d.) resulted in a 63% decrease of sildenafil AUC and a 55% decrease in sildenafil C max. Concomitant administration of strong CYP3A4 inducers, such as rifampin, is expected to cause greater decreases in plasma levels of sildenafil. Single doses of antacid (magnesium hydroxide/aluminum hydroxide) did not affect the bioavailability of sildenafil tablets. In healthy male volunteers, there was no evidence of a clinically significant effect of azithromycin (500 mg sildenafil 25 mg tablets 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. The frequency of patients reporting improvement of erections in response to a global question in four of the randomized, double-blind, parallel, placebo-controlled fixed dose studies (1797 patients) of 12 to 24 weeks duration is shown in Figure 7.
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Sixty-three percent, 74%, and 82% of the patients on 25 mg, 50 mg and 100 mg of sildenafil tablets, respectively, reported an improvement in their erections, compared to 24% on placebo.
- The proper administration of sildenafil involves taking it on an empty stomach or with light food.
- Seek immediate medical help if experiencing chest pain or prolonged erection.
- Sildenafil's interaction with other drugs can alter its effectiveness.
- Regular check-ups are recommended for long-term users.
- Sildenafil does not cause spontaneous erections without sexual stimulation.
- Never combine sildenafil 200 mg with recreational drugs like poppers.
In the titration studies (n=644) (with most patients eventually receiving 100 mg), results were similar.
2.5 Dosage Adjustments in Special Populations
In clinical studies, sildenafil tablets 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. Sildenafil tablets were evaluated primarily at doses of 25 mg, 50 mg and 100 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). Sildenafil tablets were administered to more than 3,000 patients aged 19 to 87 years, with ED of various etiologies (organic, psychogenic, mixed) with a mean duration of 5 years. Sildenafil tablets demonstrated statistically significant improvement compared to placebo in all 21 studies. Efficacy Endpoints in Controlled Clinical Studies The effectiveness of sildenafil tablets were evaluated in most studies using several assessment instruments.
Sildenafil (Generic Viagra)
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. In addition, patients were asked a global efficacy question and an optional partner questionnaire was administered. Efficacy Results from Controlled Clinical Studies The effect on one of the major end points, maintenance of erections after penetration, is shown in Figure 6, for the pooled results of 5 fixed-dose, dose-response studies of greater than one month duration, showing response according to baseline function. Figure 6 shows that regardless of the canadian sildenafil citrate baseline levels of function, subsequent function in patients treated with sildenafil tablets were better than that seen in patients treated with placebo. At the same time, on-treatment function was better in treated patients who were less impaired at baseline. Overall treatment p<0.0001 Figure 7. Percentage of Patients Reporting an Improvement in Erections .
| Use Case | Patient Group | Effect Duration | Common Side Effects |
|---|---|---|---|
| Erectile Dysfunction | Men aged 40-70 | 4-6 hours | Headache, flushing, nasal congestion |
| Pulmonary Hypertension | Adults with PAH | 4-6 hours | Dizziness, visual disturbances |
| Off-label Sexual Enhancement | Men over 40 | Varies | Muscle aches, digestive upset |
| Sildenafil for High Altitude Sickness | Travelers | 4-6 hours | Low blood pressure, dizziness |
The patients in studies had varying degrees of ED.
| Side Effect | Frequency | Severity | Management Suggestions |
|---|---|---|---|
| Headache | Common | Mild | Analgesics, hydration |
| Visual disturbances | Less common | Mild-moderate | Discontinue use if persistent |
| Dizziness | Common | Mild | Sit or lie down, avoid driving |
| Priapism | Rare | Severe | Seek immediate medical attention |
| Hearing loss | Very rare | Severe | Discontinue medication, seek help |
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.
- Sildenafil 200 mg is not recommended for women or children.
- Overuse can lead to serious cardiovascular problems.
- The medication should be part of a comprehensive treatment plan.
- Use caution if combining sildenafil with other ED medications.
- Inform your healthcare provider of all health conditions before use.
- Ensure correct timing to maximize the drug's effectiveness.
In many of the studies, of both fixed dose and titration designs, daily diaries were kept by patients.
5.5 Hypotension when Co-administered with Alpha-blockers or Anti-hypertensives
These effects on the metabolite are not expected to be of clinical consequence. Effects of Sildenafil Tablets on Other Drugs In vitro studies: Sildenafil is a weak inhibitor of the CYP isoforms 1A2, 2C9, 2C19, 2D6, 2E1 and 3A4 (IC50 >150 μM). Given sildenafil peak plasma concentrations of approximately 1 μM after recommended doses, it is unlikely that sildenafil tablets will alter the clearance of substrates of these isoenzymes. In vivo studies: No significant interactions were shown with tolbutamide (250 mg) or warfarin (40 mg), both of which are metabolized by CYP2C9. In a study of healthy male volunteers, sildenafil (100 mg) did not affect the steady state pharmacokinetics of the HIV protease inhibitors, saquinavir and ritonavir, both of which are CYP3A4 substrates.
Common Adverse Effects
Sildenafil tablets (50 mg) did not potentiate the increase in bleeding time caused by aspirin (150 mg). Sildenafil at steady state, at a dose not approved for the treatment of erectile dysfunction (80 mg t.i.d.) resulted in a 50% increase in AUC and a 42% increase in C maxof bosentan (125 mg b.i.d.). 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 20-and 38-times, for male and female rats, respectively, the exposures observed in human males given the Maximum Recommended Human Dose (MRHD) of 100 mg. Sildenafil was not carcinogenic when administered to mice for 18 to 21 months at dosages up to the Maximum Tolerated Dose (MTD) of 10 mg/kg/day, approximately 0.4 times the MRHD on a mg/m2 basis in a 50 kg subject. Impairment of Fertility There was no impairment of fertility in rats given sildenafil up to 60 mg/kg/day for 36 days to females and 102 days to males, a dose producing an AUC value of more than 25 times the human male AUC. In these studies, involving about 1600 patients, analyses of patient diaries showed no effect of sildenafil tablets on rates of attempted intercourse (about 2 per week), but there was clear treatment-related improvement in sexual function: per patient weekly success rates averaged 1.3 on 50 to 100 mg of sildenafil tablets vs 0.4 on placebo; similarly, group mean success rates (total successes divided by total attempts) were about 66% on sildenafil tablets vs about 20% on placebo.
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Due to age-differences in plasma protein binding, the corresponding increase in the AUC of free (unbound) sildenafil and its active N-desmethyl metabolite were 45% and 57%, respectively [ see Dosage and Administration (2.5),and Use in Specific Populations (8.5)] Renal Impairment:In volunteers with mild (CLcr=50 to 80 mL/min) and moderate (CLcr=30 to 49 mL/min) renal impairment, the pharmacokinetics of a single oral dose of sildenafil tablets (50 mg) were not altered. In volunteers with severe (CLcr <30 mL/min) renal impairment, sildenafil clearance was reduced, resulting in approximately doubling of AUC and C maxcompared to age-matched volunteers with no renal impairment [see Dosage and Administration (2.5),and Use in Specific Populations (8.6)]. In addition, N-desmethyl metabolite AUC and C maxvalues significantly increased by 200% and 79%, respectively in subjects with severe renal impairment compared to subjects with normal renal function. Hepatic Impairment:In volunteers with hepatic impairment (Child-Pugh Class A and B), sildenafil clearance was reduced, resulting in increases in AUC (85%) and C max(47%) compared to age-matched volunteers with no hepatic impairment. The pharmacokinetics of sildenafil in patients with severely impaired hepatic function (Child-Pugh Class C) have not been studied [see Dosage and Administration (2.5),and Use in Specific Populations (8.7)].
Terms and Conditions
Therefore, age >65, hepatic impairment and severe renal impairment are associated with increased plasma levels of sildenafil. A starting oral dose of 25 mg should be considered in those patients [see Dosage and Administration (2.5)]. Drug Interaction Studies Effects of Other Drugs on Sildenafil Tablets Sildenafil metabolism is principally mediated by CYP3A4 (major route) and CYP2C9 (minor route). In vivo studies: Cimetidine (800 mg), a nonspecific CYP inhibitor, caused a 56% increase in plasma sildenafil concentrations when co-administered with sildenafil tablets (50 mg) to healthy volunteers. When a single 100 mg dose of sildenafil tablets were administered with erythromycin, a moderate CYP3A4 inhibitor, at steady state (500 mg bid for 5 days), there was a 160% increase in sildenafil C maxand a 182% increase in sildenafil AUC. During 3 to 6 months of double-blind treatment or longer-term (1 year), open-label studies, few patients withdrew from active treatment for any reason, including lack of effectiveness.
- Sildenafil 200 mg is a high dose used to treat severe erectile dysfunction.
- This medication increases blood flow to the penis for improved erection.
- It is important to follow a doctor's prescription for 200 mg dosage.
- Common side effects include headaches, flushing, and nasal congestion.
- Sildenafil should not be mixed with nitrates due to risk of low blood pressure.
- The drug is typically taken about an hour before sexual activity.