Isocor is a long acting nitrate preparation. It has very little utility in the treatment of high BP. It is given for symptomatic relief of angina, which you do not seem to have. Giving up nitrates for any reason is not a dangerous thing. Isosorbide dinitrate (Sorbitrate) is the same salt, which is shorter acting. You can take it 3 times a day, although I feel that you do not need it if you have no angina.