Inhibitory effect of zonisamide on human carbonic anhydrase in vitro.

We examined the relative potencies of zonisamide (CAS 68291-97-4) to acetazolamide in inhibiting carbonic anhydrases in human erythrocytes and purified human carbonic anhydrase I and II in vitro and found them to be about 1/150, 1/8 and 1/188, respectively. The IC50 values of zonisamide and acetazolamide for the inhibition of erythrocyte enzymes were close to those of purified carbonic anhydrase II. This result indicates that zonisamide actually differs from acetazolamide in their actions on the physiological events which are coupled with CO2 hydration in vivo.