DPI is an irreversible inhibitor of iNOS and eNOS with IC50 values of 50 nM and 0.3 µM, respectively. This inhibition is potent, irreversible, and time and temperature dependent. NADPH, NADP+, and 2'5'-ADP block the inhibitory action of DPI. Similarly, FAD or FMN protect NOS from inhibition by DPI.