Final answer:
Phosphodiesterase inhibitors, such as sildenafil, are drugs that inhibit the degradation of cAMP by PDE enzymes. Originally studied for heart conditions, sildenafil was later approved for treating erectile dysfunction and has been very successful in this regard, though it comes with warnings for certain cardiac patients.
Step-by-step explanation:
Phosphodiesterase Inhibitors and Their Medical Applications
Phosphodiesterase (PDE) inhibitors are a class of drugs that block the action of the enzyme phosphodiesterase. PDE is responsible for degrading cyclic adenosine monophosphate (cAMP), thus, inhibiting PDE can prolong the action of cAMP in signaling pathways. One well-known PDE inhibitor is sildenafil, which was initially investigated for the treatment of hypertension and angina pectoris but later found to be effective in treating erectile dysfunction (ED).
During the clinical trials in the 1990s, sildenafil, a PDE5 inhibitor, did not prove to be effective in treating heart conditions but was discovered to enhance erections in men. This eventually led to the FDA approving the drug, marketed as Viagra®, for the treatment of ED. Generated sales of PDE inhibitors like sildenafil now surpass a billion dollars annually, and they are reported to treat about 70 to 85 percent of ED cases. However, there are important considerations for men with cardiac disease, especially those taking nitrates, due to the risk associated with sildenafil.