Duration of action
Among the three PDE5 inhibitors, the half-life and thus duration of action is the pharmacologic parameter that is the most strikingly dissimilar. The half-life of tadalafil is 17.5 hours in normal healthy men and 21.6 hours in elderly men, while the half-lives of sildenafil and vardenafil are similar at 4 hours. This longer half-life provides a therapeutic window of 36 hours for generic tadalafil.
The risks of a longer half-life have yet to be completely elucidated, but there does not appear to be any higher mortality with tadalafil (Cialis) compared to the other PDE5 inhibitors. One difference resulting from the half-life disparity is that emergent treatment with nitrate medications must be deferred for at least 48 hours after ingestion of tadalafil, compared with 24 hours for sildenafil (Vaigra) and vardenafil (Levitra).
Pharmacologic treatments for ED prior to tadalafil, including prostaglandin intracavernosal injections or intra-urethral pellets, as well as the other two PDE5 inhibitors, all have a short half-life. For this reason, historically it has been necessary for ED treatments to be dosed immediately prior to attempting intercourse. A drawback to this necessary dosing schedule for short half-life ED treatments is potential performance anxiety. The therapeutic window of 36 hours of canadian tadalafil allows the patient more freedom to choose the timing and setting of the sexual encounter with his partner.
Other benefits of tadalafil’s longer half-life are still being explored. The FDA recently expanded the indications for tadalafil to once-daily dosing for the treatment of ED. The longer half-life provides a steady state of serum drug concentration with low dose, once-daily administration, a benefit not shared with the other two PDE5 inhibitors.