Pharmacokinetic Interaction
Carbamazepine may decrease the serum concentration of olanzapine by about 50% (25%-71%) by inDuction of CYP1A2 (and possibly UGT) enzymes.
Reversal of inDuction
Monitor for increased olanzapine effects/toxicities if carbamazepine is discontinued.
Case report: A patient on stable doses of carbamazepine (600 mg) and olanzapine (15 mg) experienced a 114% increase in serum olanzapine concentration several weeks after discontinuation of carbamazepine (Licht et al, 2000).
InDuction (and reversal of inDuction) is Delayed.
Pharmacodynamic interactions
Nothing noteworthy. No overlapping mechanisms. Both medications can cause neutropenia and, rarely, agranulocytosis but risk is not increased with the combination. As with many psychotropic combos, there may be additive sedative effects.
The Visual Mnemonics
The CYP1A4 mnemonic frame of trees and axes is described here. Similar interactions are expected between carbamazepine and any of the "tree" medications.
Bergemann, N., Frick, A., Parzer, P., & Kopitz, J. (2004). Olanzapine plasma concentration, average daily dose, and interaction with co-medication in schizophrenic patients. Pharmacopsychiatry, 37(02), 63-68.
Lucas, R. A., Gilfillan, D. J., & Bergstrom, R. F. (1998). A pharmacokinetic interaction between carbamazepine and olanzapine: observations on possible mechanism. European journal of clinical pharmacology, 54, 639-643.
Licht, R. W., Olesen, O. V., Friis, P., & Laustsen, T. (2000). Olanzapine serum concentrations lowered by concomitant treatment with carbamazepine. Journal of Clinical Psychopharmacology, 20(1), 110-112.
Olesen, O. V., & Linnet, K. (1999). Olanzapine serum concentrations in psychiatric patients given standard doses: the influence of comedication. Therapeutic drug monitoring, 21(1), 87-90.