Imdur (Isosorbide Mononitrate) Extended-Release Tablet Splitting
Imdur (isosorbide mononitrate) 30 mg extended-release tablets should not be split in half as this would compromise the extended-release mechanism and potentially lead to improper dosing and increased risk of adverse effects.
Why Imdur ER Tablets Should Not Be Split
The FDA-approved drug labeling for isosorbide mononitrate extended-release tablets specifically states that these tablets "should not be chewed or crushed and should be swallowed together with a half-glassful of fluid" 1. This warning is critical because:
- Splitting extended-release formulations disrupts the controlled-release mechanism
- This can lead to dose-dumping (immediate release of the full medication dose)
- Potential consequences include:
- Increased risk of headaches and hypotension shortly after administration
- Shortened duration of action
- Loss of the intended 24-hour coverage
Proper Dosing of Isosorbide Mononitrate ER
According to the FDA label, the proper dosing approach is:
- Starting dose: 30 mg once daily (as a single intact tablet)
- Timing: Take in the morning upon arising
- Titration: After several days, dosage may be increased to 60 mg once daily, and rarely up to 120 mg or 240 mg 1
Alternative Options
If a lower dose is needed, consider these alternatives:
- Use the lowest available strength (30 mg) as a whole tablet
- Consult with the prescriber about switching to immediate-release isosorbide mononitrate formulations if lower doses are required
- Consider alternative medications in the same class if appropriate for the patient's condition
Clinical Implications
Research shows that once-daily dosing of intact extended-release isosorbide mononitrate tablets provides:
- Effective antianginal prophylaxis for up to 12 hours 2
- Better exercise tolerance compared to twice-daily regimens 3
- Significantly lower anginal attack rates compared to placebo 3
- Rapid onset of action (within 1 hour) with measurable effects 4
Common Pitfalls to Avoid
- Never split, crush, or chew extended-release nitrate formulations
- Avoid abrupt discontinuation as this may exacerbate anginal symptoms 2
- Be aware that headache is a common side effect (occurs in about 28% of patients), but usually improves with continued therapy 4
For patients with heart failure requiring combination therapy with hydralazine, the fixed-dose combination products should be used rather than attempting to split individual components 5.
Remember that patient compliance is significantly better with once-daily administration of intact extended-release isosorbide mononitrate than with multiple daily dosing regimens 2, which further supports maintaining the integrity of the extended-release formulation.