Sildenafil dosing question

Sildenafil is approximately 4,000-fold more selective for PDE5 compared to PDE3.

PDE3 is involved in control of cardiac contractility. This lower selectivity is thought to be the basis for abnormalities related to color vision [see Clinical Pharmacology (12.2)].

• Sildenafil's molecular weight is 666.7 g/mol for the free base.
• The citrate salt formulation improves solubility and absorption.
• Taking it after a large, fatty dinner may mean waiting 2 hours for full effect.
• It is not recommended for men with severe hypotension (BP <90/50).
• Can be used by men with stable coronary artery disease on appropriate therapy.
• The medication's patent expiration led to a substantial price decrease.
• Some men may experience dyspepsia (indigestion) as a side effect.
• It is important to rule out hypogonadism (low testosterone) as a cause of ED.
• The pill does not work if the nerves or blood supply to the penis are severely damaged.
• Patient assistance programs may be available for brand-name Viagra.
• Honesty with your doctor about all health issues is crucial for safe use.

In addition to human corpus cavernosum smooth muscle, PDE5 is also found in other tissues including platelets, vascular and visceral smooth muscle, and skeletal muscle, brain, heart, liver, kidney, lung, pancreas, prostate, bladder, testis, and seminal vesicle.

• The drug's action is localized to the penis; systemic effects are generally mild.
• Starting at a low dose allows assessment of individual pharmacokinetics.
• It is not a "party drug" and using it recreationally can be hazardous.
• Men with multiple myeloma or leukemia may have contraindications.
• Can be used by men who have undergone kidney transplantation, with doctor approval.
• The cost-effectiveness of generic sildenafil has increased treatment access.
• Some men may find the side effects diminish with continued use.
• It does not treat underlying vascular disease, a common cause of ED.
• Penile implants or injections are alternatives if oral therapy fails.
• The decision to use medication should be a shared one between patient and doctor.
• Regular check-ups are important to monitor for any new health developments.

The inhibition of PDE5 in some of these tissues by sildenafil may be the basis for the enhanced platelet antiaggregatory activity of NO observed in vitro, an inhibition of platelet thrombus formation in vivo and peripheral arterial-venous dilatation in vivo.

Medical uses

The clinical relevance of this finding to men treated with VIAGRA for ED is not known. Nervous: seizure, seizure recurrence, anxiety, and transient global amnesia. Hearing: Cases of sudden decrease or loss of hearing have been reported postmarketing in temporal association with the use of PDE5 inhibitors, including VIAGRA. It is not possible to determine whether these reported events are related directly to the use of VIAGRA, to the patient's underlying risk factors for hearing loss, a combination of these factors, or to other factors [see Warnings and Precautions (5.4) and Patient Counseling Information (17)]. Ocular: diplopia, temporary vision loss/decreased vision, ocular redness or bloodshot appearance, ocular burning, ocular swelling/pressure, increased intraocular pressure, retinal edema, retinal vascular disease or bleeding, and vitreous traction/detachment.

How to take it

Most, but not all, of these patients had underlying anatomic or vascular risk factors for developing NAION, including but not necessarily limited to: low cup to disc ratio ("crowded disc"), age over 50, diabetes, hypertension, coronary artery disease, hyperlipidemia and smoking [see Warnings and Precautions (5.3) and Patient Counseling Information (17)]. Urogenital: prolonged erection, priapism [see Warnings and Precautions (5.2) and Patient Counseling Information (17)], and hematuria. Administration of VIAGRA with nitric oxide donors such as organic nitrates or organic nitrites in any form is contraindicated. Consistent with its known effects on the nitric oxide/cGMP pathway, VIAGRA was shown to potentiate the hypotensive effects of nitrates [see Dosage and Administration (2.3), Contraindications (4.1), Clinical Pharmacology (12.2)]. Use caution when co-administering alpha-blockers with VIAGRA because of potential additive blood viagra over the counter pressure-lowering effects. Effects of VIAGRA on Erectile Response: In eight double-blind, placebo-controlled crossover studies of patients with either organic or psychogenic erectile dysfunction, sexual stimulation resulted in improved erections, as assessed by an objective measurement of hardness and duration of erections (RigiScan®), after VIAGRA administration compared with placebo.

Effects of VIAGRA on Blood Pressure: Single oral doses of sildenafil (100 mg) administered to healthy volunteers produced decreases in sitting blood pressure (mean maximum decrease in systolic/diastolic blood pressure of 8.3/5.3 mmHg).

• The 25 mg dose can be part of a tailored treatment plan prescribed by your doctor.
• Some men might find 25 mg sufficient for achieving desired results.
• Always discuss any side effects or concerns with your healthcare provider.
• Viagra’s onset of action is usually within 30 to 60 minutes.
• Combining Viagra with high-fat meals can delay its effects.
• Age may influence the appropriate dosage of Viagra.
• Lifestyle factors, such as smoking, can impact Viagra's effectiveness.

Larger effects were recorded among patients receiving concomitant nitrates [see Contraindications (4.1)]. Figure 1: Mean Change from Baseline in Sitting Systolic Blood Pressure, Healthy Volunteers.

Effects of VIAGRA on Blood Pressure When Nitroglycerin is Subsequently Administered: Based on the pharmacokinetic profile of a single 100 mg oral dose given to healthy normal volunteers, the plasma levels of sildenafil at 24 hours post dose are approximately 2 ng/mL (compared to peak plasma levels of approximately 440 ng/mL).

Product Description

No overall differences in safety or efficacy were observed between older (≥ 65 years of age) and younger (< 65 years of age) subjects. However, since higher plasma levels may increase the incidence of adverse reactions, a starting dose of 25 mg should be considered in older subjects due to the higher systemic exposure [see Dosage and Administration (2.5)]. No dose adjustment is required generic viagra sildenafil citrate 50 mg for mild (CLcr=50–80 mL/min) and moderate (CLcr=30–49 mL/min) renal impairment. In volunteers with severe renal impairment (Clcr<30 mL/min), sildenafil clearance was reduced, resulting in higher plasma exposure of sildenafil (~2 fold), approximately doubling of Cmax and AUC. A starting dose of 25 mg should be considered in patients with severe renal impairment [see Dosage and Administration (2.5) and Clinical Pharmacology (12.3)].

Viagra and children

In volunteers with hepatic impairment (Child-Pugh Class A and B), sildenafil clearance was reduced, resulting in higher plasma exposure of sildenafil (47% for Cmax and 85% for AUC). The pharmacokinetics of sildenafil in patients with severely impaired hepatic function (Child-Pugh Class C) have not been studied. A starting dose of 25 mg should be considered in patients with any degree of hepatic impairment [see Dosage and Administration (2.5) viagra tablet for sex and Clinical Pharmacology (12.3)]. In studies with healthy volunteers of single doses up to 800 mg, adverse reactions were similar to those seen at lower doses but incidence rates and severities were increased. VIAGRA is formulated as blue, film-coated rounded-diamond-shaped tablets equivalent to 25 mg, 50 mg and 100 mg of sildenafil for oral administration. In the following patients: age >65 years, hepatic impairment (e.g., cirrhosis), severe renal impairment (e.g., creatinine clearance <30 mL/min), and concomitant use of erythromycin or strong CYP3A4 inhibitors, plasma levels of sildenafil at 24 hours post dose have been found to be 3 to 8 times higher than those seen in healthy volunteers.

Mechanism of action

There are no data with the use of VIAGRA in pregnant women to inform any drug-associated risks for adverse developmental outcomes. Animal reproduction studies conducted with sildenafil did not show adverse developmental outcomes when administered during organogenesis in rats and rabbits at oral doses up to 16 and 32 times, respectively, the maximum recommended human dose (MRHD) of 100 mg/day on a mg/m2 basis (see Data). No evidence of teratogenicity, embryotoxicity or fetotoxicity was observed in rats and rabbits which received oral doses up to 200 mg/kg/day during organogenesis. These doses represent, respectively, about 16 and 32 times the MRHD on a mg/m2 basis in a 50 kg subject. In the rat pre- and postnatal development study, the no observed adverse effect dose was 30 mg/kg/day given for 36 days, about 2 times the MRHD on a mg/m2 basis in a 50 kg subject.

Is Viagra’s dosage based on weight?

VIAGRA is not indicated for use in pediatric patients. Safety and effectiveness have not been established in pediatric patients. Healthy elderly volunteers (65 years or over) had a reduced clearance of sildenafil resulting in approximately 84% and 107% higher plasma AUC values of sildenafil and its active N-desmethyl metabolite, respectively, compared to those seen in healthy young volunteers (18–45 years) [see Clinical Pharmacology (12.3)]. 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 Clinical Pharmacology (12.3)]. Of the total number of subjects in clinical studies of Viagra, 18% were 65 years and older, while 2% were 75 years and older. Although plasma levels of sildenafil at 24 hours post dose are much lower than at peak concentration, it is unknown whether nitrates can be safely co-administered at this time point [see Contraindications (4.1)].

• 25 mg Viagra is often used for those who experience side effects at higher doses.
• Regular use of Viagra can improve erectile response over time.
• The medication works by increasing blood flow to the penis.
• Viagra should not be taken more than once per day.
• Consult your doctor if you experience visual disturbances while taking Viagra.
• Patients with heart problems should be cautious and inform their doctor.
• Viagra is not a cure but can help manage erectile dysfunction symptoms.

Effects of VIAGRA on Blood Pressure When Co-administered with Alpha-Blockers: Three double-blind, placebo-controlled, randomized, two-way crossover studies were conducted to assess the interaction of VIAGRA with doxazosin, an alpha-adrenergic blocking agent.

Thereafter, 17 subjects were treated with VIAGRA 25 mg or matching placebo in combination with doxazosin 4 mg (15 subjects) or doxazosin 8 mg (2 subjects). For the 17 subjects who received VIAGRA 25 mg and matching placebo, the placebo-subtracted mean maximum decreases from baseline (95% CI) in systolic blood pressure were as follows: The mean profiles of the change from baseline in standing systolic blood pressure in subjects treated with doxazosin in combination with 25 mg VIAGRA or matching placebo are shown in Figure 2.

Dosing & Uses

When VIAGRA is co-administered with an alpha-blocker, patients should be stable on alpha-blocker therapy prior to initiating VIAGRA treatment and VIAGRA should be initiated at the lowest dose [see Dosage and Administration (2.3),Warnings and Precautions (5.5), Clinical Pharmacology (12.2)]. When VIAGRA 100 mg was co-administered with amlodipine (5 mg or 10 mg) to hypertensive patients, the mean additional reduction on supine blood pressure was 8 mmHg systolic and 7 mmHg diastolic [see Warnings and Precautions (5.5), Clinical Pharmacology (12.2)]. Co-administration of ritonavir, a strong CYP3A4 inhibitor, greatly increased the systemic exposure of sildenafil (11-fold increase in AUC). It is therefore recommended not to exceed a maximum single dose of 25 mg of VIAGRA in a 48 hour period [see Dosage and Administration (2.4), Warnings and Precautions (5.6), Clinical Pharmacology (12.3)]. Co-administration of erythromycin, a moderate CYP3A4 inhibitor, resulted in a 160% and 182% increases in sildenafil Cmax and AUC, respectively.

Clinical Uses

Co-administration of saquinavir, a strong CYP3A4 inhibitor, resulted in 140% and 210% increases in sildenafil Cmax and AUC, respectively. Stronger CYP3A4 inhibitors such as ketoconazole or itraconazole could be expected to have greater effects than seen with saquinavir. A starting dose of 25 mg of VIAGRA should be considered in patients taking erythromycin or strong CYP3A4 inhibitors (such as saquinavir, ketoconazole, itraconazole) [see Dosage and Administration (2.4), Clinical Pharmacology (12.3)]. In a drug-drug interaction study sildenafil 50 mg given with alcohol 0.5 g/kg in which mean maximum blood alcohol levels of 0.08% was achieved, sildenafil did not potentiate the hypotensive effect of alcohol in healthy volunteers [see Clinical Pharmacology (12.2)]. VIAGRA is not indicated for use in females.