[Tolerance to a sustained release form of isosorbide dinitrate: comparison between 20 mg four times and 40 mg twice-daily administrations].

Attenuation of antianginal effects of oral isosorbide dinitrate in a sustained release from (ISDN-SR) were studied using the treadmill exercise test in eleven patients with stable exertional angina and a positive exercise test. We compared the four-time-daily administration of 20 mg with a twice-daily regimen of 40 mg for 10 days using the double-blind, crossover method. On the 1st day of the administration, with both regimens, the treadmill walking time, the time to 1mm and 2mm ST depression, and several hemodynamic parameters increased significantly. These improvements were reduced gradually on day 5 and day 10 after the administration. In the comparison between the four-time-daily and two-time-daily regimens, the former application showed clearer antianginal and hemodynamic effects than the latter regimen, but these effects were attenuated more markedly in the four-time daily administration. With both dosage regimens, the plasma ISDN concentrations increased gradually. With the long-term four-time-daily regimen, the time-to-time changes of the ISDN concentration were smaller each day. These data suggest that tolerance to oral ISDN-SR exists even if it is applied only two time daily, but its degree is less than when a four-time-daily dose in administered.