If you experience a prolonged or painful erection for 4 hours or more, contact your doctor immediately. Contraindications Nitrates increase cGMP formation, while sildenafil inhibits cGMP degradation causing the combination to produce severe life-threatening hypotension synergistically; coadministration of sildenafil with nitrates is contraindicated. Those with pre-existing conditions should always consult a healthcare provider before taking new medications or supplements. Sildenafil Viagra is used to treat erectile dysfunction impotence; inability to get or keep an erection in men. Using this medicine with any of the following may cause an increased risk of certain side effects but may be unavoidable in some cases. There are no antidotes available for sildenafil. The service is convenient and private These chewables use the same active ingredients as Viagra, Cialis, and Levitra sildenafil, tadalafil, and vardenafil Chewables may suit people who cannot swallow pills A person does not need water to take the medication in chewable form The prices are competitive Automatic refills every 30 days Cons of Using BlueChew Health insurance companies do not cover the cost.Medications Prescribed: Viagra, Cialis, Cialis Daily, Levitra, tadalafil, sildenafil, vardenafil. Generic offered: Yes. Why We Chose It. The simple combination of Rex MD’s online platform, its helpful customer service, and the abundance of ED treatment options make it a one-stop shop for all your sexual health needs. This means that 4 hours after you take a dose, your body has cleared half of the dose. In most cases, it takes about 5 half-lives for your body to completely remove a drug from your system. So. Sildenafil is used to treat erectile dysfunction (ED) and to reduce blood pressure in pulmonary arterial hypertension (PAH). It is taken when needed for ED and daily for PAH. A headache, stomach upsets, and flushing are the main side effects, and it should not be taken within 24 hours of a nitrate. 5. Tips.