Improvement of schizophrenic symptoms and changes in plasma HVA concentrations, plasma anti-D2 and anti-5-HT2 receptor activities with clozapine

In order to investigate the biological mechanisms underlying the clinical efficacy of clozapine, 200 mg/day of clozapine was added to the drug regimens of 19 patients with chronic, anti-psychotic-resistant schizophrenia, and the plasma homovanillic acid (HVA), clozapine concentrations, anti-dopamine D2 and anti-serotonin 5-HT 2 receptor activities were measured. After 28 days, six patients showed an improvement of more than 20% over baseline Brief Psychiatric Rating Scale (BPRS) scores. Mean plasma HVA concentrations and anti-D 2 receptor activities did not change significantly in the entire group or in the six patients showing improvement. However, anti-5-HT 2 receptor activities increased significantly in all 19 patients. Changes in BPRS scores did not correlate significantly with changes in plasma HVA or with changes in clozapine concentrations, or with anti-D 2 and anti-5-HT 2 receptor activities.