Flavoxate, a potent phosphodiesterase inhibitor.

The c-AMP phosphodiesterase inhibiting properties of flavoxate and of its main metabolite i.e. 3-methylflavone-8-carboxylic acid (MFCA), were assayed in vitro and compared to those of theophylline. Flavoxate and MFCA are competitive phosphodiesterase inhibitors, and are 21 and respectively 5 times more potent than theophylline. The smooth muscle relaxing activity of flavoxate possibly relies on this enzymatic mechanism.