Do not press on the plunger of the syringe. Use protective measures and ask your doctor if you have any questions about this. Deaths were first reported after approximately one year of use, and hence sildenafil, particularly chronic use, is not recommended in pediatric patients with PAH. Using alcohol or tobacco with certain medicines may also cause interactions to occur. You may take this medicine with or without food.Available strengths: 25 mg, 50 mg, mg Viagra comes in these strengths: 25 milligram (mg), 50 mg, and mg. Other forms of sildenafil (the active drug in Viagra) comes in other strengths. Generic sildenafil is covered by most Medicare and insurance plans, but some pharmacy coupons or cash prices may be lower. Get sildenafil for as low as $, which is 95% .  · Maximum dose: 20 mg orally three times a day. Injection: Initial dose: or 10 mg IV bolus three times a day. Comments: No greater efficacy was achieved with oral doses higher than the maximum recommended dose. A 10 mg injection dose is predicted to provide pharmacological effect equivalent to the 20 mg oral dose.