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A serious drop in blood pressure can lead to dizziness, fainting, and rarely heart attack or stroke.

Do not use sildenafil with any of the following: certain drugs used to treat chest pain/angina (nitrates such as nitroglycerin, isosorbide), recreational drugs called "poppers" containing amyl nitrate, amyl nitrite, or butyl nitrite. If you are also taking an alpha blocker medication (such as doxazosin, tamsulosin) to treat an enlarged prostate/BPH or high blood pressure, your blood pressure may get too low which can lead to dizziness or fainting.

Your doctor may start treatment with a lower dose of sildenafil to minimize your risk of low blood pressure.

Other medications can affect the removal of sildenafil from your body, which may affect how sildenafil works. Examples include azole antifungals (such as itraconazole, ketoconazole), macrolide antibiotics (such as clarithromycin, erythromycin), HIV protease inhibitors (such as ritonavir, saquinavir), hepatitis C virus protease inhibitors (such as boceprevir, telaprevir), mifepristone, rifampin, among others.

Do not take this medication with any other product that contains sildenafil or other similar medications for erectile dysfunction-ED or pulmonary hypertension (such as tadalafil, vardenafil).

If someone has overdosed and has serious symptoms such as passing out or trouble breathing, call 911.

Otherwise, call a poison control center right away.

US residents can call their local poison control center at 1-800-222-1222.

Canada residents can call a provincial poison control center.

Symptoms of overdose may include severe dizziness, fainting, painful/prolonged erection. Store at room temperature away from light and moisture. In eliciting its mechanism of action, sildenafil ultimately prevents or minimizes the breakdown of cyclic guanosine monophosphate (cGMP) by inhibiting cGMP specific phosphodiesterase type 5 (PDE5) 11,12,13,14,15,discount viagra no prescription 16,8,9 . The result of doing so allows cGMP present in both the penis and pulmonary vasculature to elicit smooth muscle relaxation and vasodilation that subsequently facilitates relief in pulmonary arterial hypertension and the increased flow of blood into the spongy erectile tissue of the penis that consequently allows it to grow in size and become erect and rigid 11,12,13,14,15,16,8,9 .

Interestingly enough, it is precisely via this mechanism why sildenafil was at first researched as a potential treatment for angina - or chest pain associated

with

Nevertheless, it is because of this mechanism that sildenafil is also indicated for treating pulmonary arterial hypertension but is also additionally notorious for interacting with various anti-anginal or anti-hypertensive agents to develop potentially rapid, excessive, and/or fatal hypotensive crises 4,5,6 . Regardless, sildenafil, among a variety of other similar or related PDE5 inhibitors, has become a common and effective treatment for erectile dysfunction and since its formal approval for medical use in the public in 1998 7 , continues to see millions of prescriptions written for it internationally.

Although the medication has historically been most popularly recognized as Pfizer's brand name Viagra, sildenafil is currently available generically and even as a non-prescription over the counter medication in some countries 10 . Type Small Molecule Groups Approved, Investigational Structure. Structure for Sildenafil (DB00203) HIP-0908 HIP0908.

Sildenafil is a phosphodiesterase-5 (PDE5) inhibitor that is predominantly employed for two primary indications: (1) the treatment of erectile dysfunction 5,8,12,13,16 ; and.

(2) treatment of pulmonary hypertension, where: a) the US FDA specifically indicates sildenafil for the treatment of pulmonary arterial hypertension (PAH) (WHO Group I) in adults to improve exercise ability and delay clinical worsening 11 . The delay in clinical worsening was demonstrated when sildenafil was added to background epoprostenol therapy 11 .

Studies establishing effectiveness were short-term (12 to 16 weeks), and included predominately patients with New York Heart Association (NYHA) Functional Class II-III symptoms and idiopathic etiology (71%) or associated with connective tissue disease (CTD) (25%) 11 ; b) the Canadian product monograph specifically indicates sildenafil for the treatment of primary pulmonary arterial hypertension (PPH) or pulmonary hypertension secondary to connective tissue disease (CTD) in adult patients with WHO functional class II or III who have not responded to conventional therapy 14 .

In addition, improvement in exercise ability and delay in clinical worsening was demonstrated in adult patients who were already stabilized on background epoprostenol therapy 14 ; and. c) the EMA product information specifically indicates sildenafil for the treatment of adult patients with pulmonary arterial hypertension classified as WHO functional class II and III, to improve exercise capacity 15 .

Efficacy has been shown in primary pulmonary hypertension and pulmonary hypertension associated with connective tissue disease 15 .

The EMA label also indicates sildenafil for the treatment of pediatric patients aged 1 year to 17 years old with pulmonary arterial hypertension 15 . Efficacy in terms of improvement of exercise capacity or pulmonary hemodynamics has been shown in primary pulmonary hypertension and pulmonary hypertension associated with congenital heart disease 15 .

Erectile Dysfunction NYHA Functional Class II-III Pulmonary arterial hypertension Pulmonary Arterial Hypertension (PAH) Contraindications & Blackbox Warnings.

Learn about our commercial Contraindications & Blackbox Warnings data. In vitro studies have shown that sildenafil is selective for phosphodiesterase-5 (PDE5) 11,12,13,discount viagra no prescription 14,15,16,8,9 . Its effect is more potent on PDE5 than on other known phosphodiesterases 11,12,13,14,15,16,8,9 . In particular, there is a 10-times selectivity over PDE6 which is involved in the phototransduction pathway in the retina 11,12,13,14,15,16,8,9 .

There is an 80-times selectivity over PDE1, and over 700-times over PDE 2, 3, 4, 7, 8, 9, 10 and 11 11,12,13,14,15,16,8,9 .

And finally, sildenafil has greater than 4,000-times selectivity for PDE5 over PDE3, the cAMP-specific phosphodiesterase isoform involved in the control of cardiac contractility 11,12,13,14,15,16,8,9 . In eight double-blind, placebo-controlled crossover studies of patients with either organic discount viagra no prescription or psychogenic erectile dysfunction, sexual stimulation resulted in improved erections, as assessed by an objective measurement of hardness and duration of erections (via the use of RigiScan®), after sildenafil administration compared with placebo 11,12,13,14,15,16,8,9 . Most studies assessed the efficacy of sildenafil approximately 60 minutes post-dose 11,12,13,14,15,16,8,9 .

The erectile response, as assessed by RigiScan®, generally increased with increasing sildenafil dose and plasma concentration 11,12,13,14,15,16,8,9 . The time course of effect was examined in one study, showing an effect for up to 4 hours but the response was diminished compared to 2 hours 11,12,13,14,15,16,8,9 .

Sildenafil causes mild and transient decreases in systemic blood pressure which, in the majority of cases, do not translate into discount viagra no prescription clinical effects 11,12,13,14,15,16,8,9 .

After chronic dosing of 80 mg, discount viagra no prescription three times a day to patients with systemic hypertension the mean change from baseline in systolic and diastolic blood pressure was a decrease of 9.4 mmHg and 9.1 mmHg respectively 11,12,13,14,15,16,8,9 . After chronic dosing of 80 mg, three times a day to patients with pulmonary arterial hypertension lesser effects in blood pressure reduction were observed (a reduction in both systolic and diastolic pressure of 2 mmHg) 11,12,13,14,15,16,8,9 .

At the recommended dose of 20 mg three times a day no reductions in systolic or diastolic pressure were seen 11,12,13,14,15,16,8,9 .

Single oral doses of sildenafil up to 100 mg in healthy volunteers produced no clinically relevant effects on ECG 11,12,13,14,15,16,8,9 .

After chronic dosing of 80 mg three times a day to patients with pulmonary arterial hypertension no clinically relevant effects on the ECG were reported either 11,12,13,14,15,16,8,9 . In a study of the hemodynamic effects of a single oral 100 mg dose of sildenafil in 14 patients with severe coronary artery disease (CAD) (> 70 % stenosis of at least one coronary artery), the mean resting systolic and diastolic blood pressures decreased by 7 % and 6 % respectively compared to baseline 11,12,13,14,15,16,8,9 . Mean pulmonary systolic blood pressure decreased by 9% 11,12,13,14,15,16,8,9 .

Sildenafil showed no effect on cardiac output and did not impair blood flow through the stenosed coronary arteries 11,12,13,14,15,16,8,9 . Mild free viagra no prescription and transient differences in color discrimination (blue/green) were detected in some subjects using the Farnsworth-Munsell 100 hue test at 1 hour following a 100 mg dose, with no effects evident after 2 hours post-dose 11,12,13,14,15,16,8,9 . The postulated mechanism for this change in color discrimination is related to inhibition of PDE6, which is involved in the phototransduction cascade of the retina 11,12,13,14,15,16,8,9 . Sildenafil has no effect on visual acuity or contrast sensitivity.

In a small size placebo-controlled study of patients with documented early age-related macular degeneration (n = 9), sildenafil (single dose, 100 mg) demonstrated no significant changes in visual tests conducted (which included visual acuity, Amsler grid, color discrimination simulated traffic light, and the Humphrey perimeter and photostress test) 11,12,13,14,15,16,8,9 .