Correlation between plasma clozapine concentration and heart rate variability in schizophrenic patients.

Forty schizophrenic patients treated with 50-600 mg/day of clozapine as monotherapy and 40 normal control subjects were tested for heart rate variability (HRV) which is mediated by the vagus nerve using acetylcholine as neurotransmitter. As compared to the control subjects, the patients showed essentially reduced HRV parameters which were negatively correlated with the plasma clozapine levels. Therefore, clozapine's anticholinergic effect is correlated to the plasma clozapine level when measured by the decrease of HRV. We suggest that HRV data might be useful as a predictor for plasma clozapine levels.