How do these drugs work?
Cialis, Levitra (Vardenafil) and Viagra™ (Sildenafil) work by selectively inhibiting an enzyme in the penis called Phosphodiesterase V (PDE V), a chemical that takes away the erection. By blocking PDE V temporarily, these medications empower the chemical, Nitric Oxide (NO) that occurs naturally with arousal to initiate, produce and maintain an erection. Patients need sexual stimulation and foreplay to release NO initiate an erection in order for these medications to be effective. They are called phosphodiesterase inhibitors.
This class of medication is a safe and effective oral treatment for men with erectile dysfunction of physical, psychological or mixed cause. However, it is important that patients should be aware of the low probability (less than 50%) that intercourse will be possible after the first dose - particularly in severe or advanced cases and especially when using Viagra or Levitra. The majority of men who stop Viagra because of apparent lack of effect will in fact respond and achieve intercourse if they continue to try again, progress from 50 mg to 100 mg, or take the pill without food on an empty stomach (3 hours after eating). Taking Viagra or Levitra on a full stomach will not only reduce their peak concentration in the body by 30 to 50% but in addition will delay their peak concentration by one hour. In other words one may have to wait after intake before initiating sexual activity. Cialis peak concentration and time before reaching maximum absorption is not affected by a full stomach. Because of this it remains my drug of choice for the treatment of ED and I always prescribe it first. In addition many of my patients experience fewer side effects with Cialis then with the other two. Finally Cialis has a long period of activity and patients are successful at intercourse up to 36 hours after taking this pill. This represents a distinct advantage from the patient’s perspective as it diminishes the need for planning. Sex can be more spontaneous and natural. Planning kills the mood. Having sex long after taking the pill makes men feel more normal! For these reasons I will first try Cialis on all my Patients and reserve Viagra and Levitra for those men who do not tolerate Cialis.