PDE-5 Inhibitors: Names and Classification
The FDA-approved phosphodiesterase-5 (PDE-5) inhibitors are sildenafil, vardenafil, tadalafil, and avanafil. 1, 2
Currently Available PDE-5 Inhibitors
First-Generation Agents
- Sildenafil (Viagra™) - The first PDE-5 inhibitor approved for erectile dysfunction 3, 4, 5
- Vardenafil (Levitra™) - Similar molecular structure to sildenafil 6, 4, 7
- Tadalafil (Cialis™) - Structurally different from sildenafil and vardenafil, with longer duration of action 8, 4, 7
Newer Agent
- Avanafil (Stendra™) - Most recently approved PDE-5 inhibitor with favorable side effect profile 2, 9, 5
Additional PDE-5 Inhibitors (Limited Availability)
Two additional agents have been studied but are not widely available in the United States:
- Mirodenafil - Evaluated in clinical trials with demonstrated efficacy 1
- Udenafil - Studied in randomized controlled trials showing improvement in erectile function 1
Key Pharmacologic Distinctions
Mechanism of Action
All PDE-5 inhibitors work by selectively inhibiting cyclic guanosine monophosphate (cGMP)-specific phosphodiesterase type-5, which reduces degradation of cGMP and allows penile smooth muscle relaxation 3, 8, 4
Duration of Action
- Sildenafil and vardenafil: Approximately 4 hours 4, 7
- Tadalafil: Approximately 36 hours 10, 4, 7
- Avanafil: Similar to sildenafil and vardenafil 2
Onset of Action
- Vardenafil: As early as 10 minutes in 21% of patients 7
- Sildenafil: As early as 14 minutes in 35% of patients 7
- Tadalafil: As early as 16 minutes in 16% of patients 7
Clinical Efficacy
All FDA-approved PDE-5 inhibitors demonstrate similar efficacy in treating erectile dysfunction, with no single agent proven superior to others. 1, 2, 11 High-quality evidence shows that these agents improve erections in 73-88% of cases compared to 26-32% with placebo 1, 11