Phosphodiesterase inhibitor
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A phosphodiesterase inhibitor is a drug that blocks one or more of the five subtypes of the enzyme phosphodiesterase (PDE), preventing the inactivation of the intracellular second messengers, cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP).
Relatively non-selective phosphodiesterase inhibitors include the minor stimulant caffeine and the bronchodilator theophylline.
Sildenafil, Tadalafil and Vardenafil are selective inhibitors of type V phosphodiesterase (PDE5), which is cGMP-specific and responsible for the degradation of cGMP in the corpus cavernosum. These phosphodiesterase inhibitors are used as remedies for erectile dysfunction.
Enoximone, which inhibits PDE IV, and milrinone, which inhibits PDE IIIc, are useful for short-term treatment of cardiac failure. Clinically these drugs mimic sympathetic stimulation and increase cardiac output.