Multi-isoform inhibitors and secondary targets of selective inhibitors Although many inhibitors are called “selective”, this is really a relative term. The compounds are termed selective based on the fact that other isoforms are only inhibited at higher concentrations. Some compounds such as dipyridamole and zardaverine are selective for a limited number of isoforms. However, some of the inhibitors that target multiple isoforms may be useful because of this property. For example, dipyridamole is a component of the stroke treatment Aggrenox (aspirin/extended-release dipyridamole).

Inhibitor PDE IC50
Sildenafil PDE1 350 nM
PDE6 50 nM
Tadalafil PDE6 2 μM
PDE11 73 nM
Vardenafil PDE6 11 nM
Zaprinast PDE1 6 μM
PDE5 0.13 μM
PDE10 22 μM
PDE11 12 μM
Zardaverine PDE3 0.5–2 μM
PDE4 0.8–4 μM
Dipyridamole PDE5 0.9 μM
PDE6 125 nM
PDE7 0.60 μM
PDE8 9 μM
PDE10 1 μM
PDE11 0.4 μM
Trequinsin PDE4 0.2–0.8 μM
PDE2 ∼1 μM
IBMX Multiple 2–50 μM