Are there other PDE enzymes? Does tadalafil inhibit other PDEs?

The term phosphodiesterase refers to a ‘‘superfamily’’  of enzymes consisting in humans of 11  families (isozymes or isoenzymes). Classification  of the PDEs is based on their structure and  whether they regulate the substrate cAMP,  cGMP, or both. The PDEs are variously distributed  throughout the body.  Different drugs have different selectivity for  inhibiting the various PDE families. For example,  a number of older compounds such as  theophylline and papaverine inhibit many or  all of the PDE isozymes including PDE5 [12–14].  In contrast, the three PDE5 inhibitors are more  selective for inhibiting PDE5 relative to the  other PDE isoenzymes. None of the PDE5 inhibitors  has any significant effect against PDEs  1–4 and 7–10, but sildenafil citrate and vardenafil  HCl do have some activity against PDE6  and tadalafil has some activity against PDE 11  [15].