Therapeutic drug monitoring (TDM) should be considered obligatory and the standard of care for carbamazepine (Hiemke et al. 2018). Therapeutic concentrations are between 4-12 µg/mL (laboratory alert <20 µg/mL) for epilepsy and have not been specifically developed for bipolar disorder. Side effects may be seen above levels of 9 µg/mL, with toxicity >40 µg/mL (Hojer, Malmlund, and Berg 1993). After starting carbamazepine, serum levels should be measured frequently, for example every three, six, and nine weeks. Then, carbamazepine levels should be monitored every two to three months thereafter or after a CYP3A4 inhibitor/inducer is added. If there is suspicion for toxicity, a carbamazepine-10,11-epxoide level may also be helpful. Clinicians should also have a low threshold to use TDM for other compounds whose metabolism may be affected while an individual is taking carbamazepine.
Please see the related answer card on common drug-drug interactions and carbamazepine.
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