Carbamazepine/oxcarbazepine and valproate have different effects on the electroconvulsive therapy seizure threshold.

Patients receiving mood stabilizers such as valproate (VAL) and carbamazepine (CMZP)/Oxcarbazepine (OX) may be referred for electroconvulsive therapy (ECT). The relative effects of these anticonvulsants on seizure threshold and seizure duration are unknown. We extracted data for a 20-month period from the medical records of patients who received bilateral ECT while on treatment with VAL (n=102) or CMZP/OX (n=31; 20 on CMZP, 11 on oxcarbazepine). Age-matched ECT-treated anticonvulsant-free patients (n=133) formed the control group. Seizure threshold in these patients had been determined by stimulus dose titration. The effect of VAL vs CMZP/OX on seizure threshold was examined using multivariable regression with adjustment for confounders. The mean (standard deviation) seizure threshold at the first ECT was highest in the CMZP/OX group (243.9 [106.1] mC), intermediate in the VAL group (177.7 [97.0] mC), and lowest in the control group (138.7 [86.0 Mc]). The regression model explained 37.5% of the variance in seizure threshold at the first ECT. Age, use of CMZP/OX, and anticonvulsant dose were each significantly associated with higher seizure threshold. CMZP/OX was associated with a higher initial ECT seizure threshold than VAL. ECT practitioners may prefer to start with a higher initial stimulus dose in patients receiving CMZP/OX or VAL, and more so for CMZP/OX than VAL, to avoid repeated sub-convulsive stimuli being administered.