Do not chew on it or break it apart. Stendra avanafil : This is an as-needed medication taken 30 minutes before sex and can last up to six hours. Soon, in , ICOS received a patent for compound IC structurally unlike sildenafil and vardenafil , and Phase 1 clinical trials began in More serious side effects may include a drop in blood pressure or an erection that lasts longer than four hours. In , Pfizer scientists discovered that sildenafil, which also inhibits the PDE5 enzyme, caused penile erection in males participating in a clinical study of a heart medicine. It’s available in 25 mg, 50 mg, and mg tablets and lasts up to 18 hours.AdComplete the Online Consultation with our Doctor. Personalize Your Needs. If Appropriate, Get a Prescription for ED from RexMD®. Free Shipping AvailableTypes: Immune Support · Sertraline · Genital Herpes · Testosterone.  · Get answers to common questions about the dosage of Cialis. What form does Cialis come in? Cialis comes as a tablet that you take by mouth. Available strengths of Cialis ( mg, 5 mg, 10 mg, 20 mg). The most common side effects with CIALIS are: headache, indigestion, back pain, muscle aches, flushing, and stuffy or runny nose. These side effects usually go away after a few hours. Men who get back pain and muscle aches usually get it 12 to 24 hours after taking CIALIS. Back pain and muscle aches usually go away within 2 days.