One quarter of a 0.5 mg tablet equals 0.125 mg
When splitting a 0.5 mg tablet into quarters, each piece represents approximately 0.125 mg (one-quarter of 0.5 mg = 0.125 mg). This is straightforward mathematics, though the actual delivered dose may vary due to tablet splitting inaccuracies.
Important Considerations About Tablet Splitting
Accuracy and Precision Issues
Tablet splitting introduces substantial dose variability that cannot be detected by weighing alone 1. Research demonstrates that:
- Split tablet fragments show high variability with coefficients of variation ranging from 8.6% to 23.3% 1
- Only 50-70% of quarter tablets comply with European Pharmacopoeia acceptance limits, with actual content ranging from 52-133% of the intended claim 1
- Most split fragments fail European Pharmacopoeia mass uniformity criteria 1
When prednisolone tablets were split into quarters, the accuracy of the best quarters (meaning the second-largest quarter fragment) was within ±15% of the target dose 2. However, this requires selecting the larger fragments, as smaller quarters showed greater deviation.
Clinical Context for Specific Medications
The evidence provides examples where quarter-tablet dosing is explicitly recommended:
- Phentermine for weight management: For some patients, a quarter tablet (9.375 mg from a 37.5 mg tablet) may be adequate, particularly for those requiring individualized lower dosing 3
- Low-dose oral minoxidil: For women of low weight, baseline low blood pressure, or cardiovascular history, starting at 0.625 mg (1/4 of a 2.5 mg tablet) is recommended 4
Practical Recommendations
If you must use a quarter of a 0.5 mg tablet (yielding approximately 0.125 mg):
- Use a tablet splitter rather than breaking by hand
- Select the second-largest quarter fragment for better accuracy 2
- Recognize that the actual dose delivered may range from 0.065 mg to 0.166 mg (52-133% of target) 1
- Consider whether this degree of variability is clinically acceptable for the specific medication and indication
When precise low-dose accuracy is critical (such as during medication tapering), pharmacy-compounded suspensions should be preferred over tablet splitting, as they provide accuracy within ±10% and higher precision 2.