How to Convert Carbamazepine µg/mL to µmol/L
Carbamazepine levels are reported in µg/mL (mg/L) in the US and in µmol/L in many other countries. The conversion factor is 4.23, from carbamazepine's molecular weight of 236.27 g/mol.
Carbamazepine µmol/L = carbamazepine µg/mL × 4.23 Carbamazepine µg/mL = carbamazepine µmol/L ÷ 4.23 Carbamazepine µg/mL to µmol/L Chart
| µg/mL | µmol/L | Context |
|---|---|---|
| 2 µg/mL | 8.5 µmol/L | Sub-therapeutic |
| 4 µg/mL | 16.9 µmol/L | Therapeutic (lower) |
| 8 µg/mL | 33.8 µmol/L | Therapeutic (mid) |
| 12 µg/mL | 50.8 µmol/L | Therapeutic (upper) |
| 15 µg/mL | 63.5 µmol/L | Above range |
| 40 µg/mL | 169.2 µmol/L | Severe toxicity |
µmol/L to µg/mL Reverse Chart
| µmol/L | µg/mL |
|---|---|
| 17 µmol/L | 4.0 µg/mL |
| 34 µmol/L | 8.0 µg/mL |
| 51 µmol/L | 12.1 µg/mL |
| 85 µmol/L | 20.1 µg/mL |
Carbamazepine Therapeutic and Toxic Ranges
| Measure | µg/mL | µmol/L |
|---|---|---|
| Therapeutic | 4–12 µg/mL | 17–51 µmol/L |
| Often effective | 4–8 µg/mL | 17–34 µmol/L |
| Toxic | Above 15 µg/mL | Above ~64 µmol/L |
Autoinduction: Why Levels Drift
Carbamazepine is unusual because it induces its own metabolism (autoinduction). A level that is therapeutic in the first days can fall over the following weeks as the liver speeds up its clearance, sometimes requiring a dose increase. It also interacts with many other medicines, so levels are rechecked after dose or drug changes.
Worked Example
Suppose a report shows 51 µmol/L and you want µg/mL:
51 ÷ 4.23 = 12.1 µg/mL 12.1 µg/mL is at the top of the therapeutic range. Converting the other way, 4 µg/mL is about 16.9 µmol/L.
Frequently Asked Questions
How do you convert carbamazepine µg/mL to µmol/L?
Multiply µg/mL by 4.23. For example, 8 µg/mL is about 33.8 µmol/L.
What is the therapeutic range?
4–12 µg/mL (17–51 µmol/L), often effective at 4–8 µg/mL.
What level is toxic?
Side effects rise above ~15 µg/mL; above ~40 µg/mL is severe toxicity.
Why do levels fall over time?
Carbamazepine autoinduces its metabolism, lowering levels over the first weeks.
References
- Medscape — Carbamazepine Level: Reference Range and Interpretation.
- Carbamazepine factor 4.23 (MW 236.27 g/mol); therapeutic range 4–12 µg/mL from standard therapeutic drug monitoring references.
Conclusion
Converting carbamazepine between µg/mL and µmol/L is a ×4.23. Keep in mind that autoinduction and drug interactions make repeat monitoring important — interpret each level with timing and clinical response alongside your provider.