Your body breaks down the ED medication at various rates.
Also, the period of activity for the drugs is four hours to 36 hours (especially for Cialis pills).
Every dose needs to be adequate to offer a full period of sexual activity, from getting an erection to orgasm.
However, is the pill ready to continue to offer effects for another cycle or penetration?
Moreover, there is...
English 
Arabic
French
Spanish
Portuguese
Deutsch
Turkish
Dutch
Italiano
Russian
Romaian
Portuguese (Brazil)
Greek