There are no antidotes available for sildenafil. Percentage of Patients Reporting an Improvement in Erections. You’ll soon start receiving the latest Mayo Clinic health information you requested in your inbox. What side effects can this medication cause? It might be a while before MED is available at your local pharmacy.Cialis is only available by prescription in the United States. Viagra: Additionally, a study from Trusted Source. found that combining L-arginine and sildenafil (Viagra) worked better for. Dosage. The dose of Cialis you need will depend on whether you’re taking it daily or as needed. Daily doses are often between and 5 milligrams (mg). The as-needed dose is usually 10 mg but can range from 5–20 mg. The typicaldose of Viagra is 50 mg. However, the dosage can range from 25– mg. Sildenafil is a medication used in the management and treatment of erectile dysfunction and pulmonary arterial hypertension. It is in the phosphodiesterase-5 inhibitor (PDE5-I) class of medications. This activity describes the indications, actions, adverse effects, and contraindications of sildenafil as an agent in the clinical setting. Knowledge .