Table 1.
Former and new reference ranges, given in molar units and mass unitsa
| Antiepileptic drug | Former reference rangeb | New reference range | Action performed | ||
|---|---|---|---|---|---|
| μmol/L | mg/L | μmol/L | mg/L | ||
| Brivaracetam | NA | NA | 1–10 | 0.2–2 | Newly established |
| Carbamazepine | 15–45 | 4–11 | 15–45 | 4–11 | None |
| Free carbamazepine | 20%–30% | None | |||
| Carbamazepine-10,11-epoxidec | 5%–15% | ||||
| Clobazamd | 0.1–1 | 0.03–0.3 | 0.1–1 | 0.03–0.3 | None |
| N-desmethylclobazamd | 1–10 | 0.3–3 | 1–10 | 0.3–3 | |
| Clonazepamd | 0.06–0.22 | 0.019–0.069 | 0.04–0.12 | 0.013–0.038 | Updated |
| Eslicarbazepine | 30–100 50–140 10–100 45–140 |
8–26 13–36 3–26 12–36 |
12–100 | 3–26 | Harmonized and updated |
| Ethosuximide | 300–600 | 42–85 | 280–700 | 39–99 | Updated |
| Felbamate | 125–250 | 30–60 | 125–250 | 30–60 | None |
| Gabapentin | 20–120 | 3–21 | 20–120 | 3–21 | None |
| Lacosamide | 10–40 | 3–10 | 10–40 | 3–10 | None |
| Lamotrigine | 10–50 10–60 |
3–13 3–15 |
10–50 | 3–13 | Harmonized |
| Levetiracetam | 30–240 | 5–41 | 30–240 | 5–41 | None |
| Oxcarbazepinee | 45–140 50–140 |
12–36 13–36 |
12–140 | 3–36 | Harmonized and updated |
| Perampanel | NA | NA | 0.25–2.85 | 0.1–1 | Newly established |
| Phenobarbital | 50–130 | 12–30 | 50–130 | 12–30 | None |
| Phenytoin | 40–80 | 10–20 | 40–80 | 10–20 | None |
| Free phenytoin | ≤10% | ||||
| Pregabalin | 10–30 | 2–5 | 10–35 | 2–6 | Updated |
| Rufinamide | 20–130 | 5–31 | 15–130 | 4–31 | Updated |
| Stiripentol | NA | NA | 15–95 | 4–22 | Newly established |
| Sulthiame | NA | NA | 5–35 | 2–10 | Newly established |
| Topiramate | 15–60 | 5–20 | 6–30 | 2–10 | Updated |
| Valproate | 250/300–600/700 | 36/43–87/101 | 300–700 | 43–101 | Harmonized |
| Free valproate | ≤10% | ||||
| Vigabatrinf | NA | NA | NA | NA | None |
| Zonisamide | 45–180 | 10–38 | 45–180 | 10–38 | None |
Notes: All serum concentrations apply to blood samples taken in drug-fasting and in pharmacokinetic steady state. Decimals rounded to nearest whole number except clobazam and perampanel.
Traditionally, serum concentrations of AEDs are given either in micrograms (μg/mL), milligrams (mg/L) or in micromoles (μmol/L). Clonazepam is usually given in nanograms (ng/mL) or nanomoles (nmol/L). Clonazepam has a minor role as an AED and is mostly used for psychiatric indications. As concentrations of most psychotropic drugs are given in ng/mL or nmol/L, we suggest that clonazepam concentrations continue to be stated in ng/mL or nmol/L.
Former reference ranges were gathered from Norwegian laboratories using The Pharmacology Portal (www.farmakologiportalen.no).10
Concentrations of carbamazepine-10,11-epoxide are usually not included in the reference range.
Usually stated in either nmol/L, μg/L or ng/mL.
Reference range applies to the active metabolite licarbazepine (formerly called monohydroxy derivative, MHD).
Vigabatrin is an irreversible enzyme inhibitor, and thus there is no direct correlation between serum concentration and effect.
Abbreviations: AED, antiepileptic drug; NA, not applicable.