onset of action  | duration of action (hours)  | doses  | |
sildenafil  | 20-30 minutes; peak action 60 minutes  | 4-6  | 25-50-100mg  | 
tadalafil  | 60-120 minutes; peak action 120 minutes  | 36-48  | 10-20mg  | 
vardenafil  | 20-30 minutes; peak action 60 minutes  | 4-6  | 5-10-20 mg  | 
The respective summary of products must be consulted before prescribing any of the drugs mentioned.
Reference:
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