How often should Isosorbide Mononitrate (ISMO, Imdur) be taken?

Isosorbide Mononitrate (ISMO, Imdur) is a medication primarily used for the prevention of angina pectoris due to coronary artery disease. The dosing regimen for ISMO typically involves taking the medication twice a day, which is denoted as BID (bis in die, or twice a day).

This schedule is designed to maintain therapeutic levels of the drug in the body while also allowing for a nitrate-free period to minimize the risk of developing tolerance, which can occur with continuous exposure to nitrates. Generally, an initial dose is taken in the morning and a second dose in the late afternoon. This timing can help manage symptoms effectively throughout the day while respecting the need for a nitrate-free interval.

Taking ISMO daily or on an as-needed basis (PRN) would not provide the necessary consistent control of angina episodes and could increase the risk of tolerance. Similarly, a thrice-daily (TID) regimen is not appropriate for this formulation, as it does not align with optimal dosing strategies used in practice. Therefore, the twice-a-day dosing is the most appropriate and clinically effective regimen for Isosorbide Mononitrate.