“Papaverine is a potent, non-specific smooth muscle relaxant which increases smooth muscle intracellular adenosine 3’,5’-monophosphate (cAMP) by its action as a non-selective cAMP phosphodiesterase inhibitor, causing vasodilatation of penile vascular and sinusoidal smooth muscle.6 Papaverine has a relatively short plasma half-life (1-2 hours) and is extensively metabolised in the liver. After intracavernosal injection, the peak serum concentration is several times lower than after extracavernosal injection, suggesting that the corpus cavernosum is a separate pharmacokinetic compartment from which elimination of papaverine is much slower than from the systemic circulation.7
A meta-analysis of the largest published studies on the use of papaverine reports that it is effective in 53% of men with ED, as measured by the ability to produce an erection of sufficient rigidity for sexual intercourse8 (E1). However, the efficacy of ICI papaverine is limited by local adverse effects, principally priapism (in 7%)8 and intracavernosal fibrosis, presenting as penile deformity or curvature (reported in one study in 50% and 95%, respectively, of long term users).9 Fibrosis is related to poor injection technique, frequent injections and long term use. Because of these adverse effects, papaverine should be restricted to informed patients in whom other medications are ineffective. Papaverine hepatotoxicity is rarely a clinical problem and may manifest either as an increase in liver transaminase concentrations, which is relatively common (> 1%), or as a drug-induced hepatitis, which is rare (< 0.1%).10”
Cavernous Neurotomy Causes Hypoxia and Fibrosis in Rat Corpus Cavernosum
Inhibition of wound contraction by papaverine: in vitro analysis with a submucosal tissue model.
Effect of trapidil and papaverine on thrombocyte aggregation and phosphodiesterase activity