Risperidone treatment was discontinued, and paliperidone, 9 mg per day, was started. Clozapine doses were slightly reduced to 575 mg in the third week as a result of increasing plasma levels. The patient's psychopathology remained stable throughout clinical treatment. Liver enzymes as well as serum levels for paliperidone and clozaÂpine were measured weekly. Aspartate transaminase levels returned to normal within 1 week, and alanine transaminase levels returned to normal after 16 days. After 4 weeks, gamma glutamyltransferase levels reached the lowest measured value, at 112 U/l, representing a 90% reduction of the initial value. Serum levels at that time were 34 ng/ml for paliperidone, 536 ng/ml for clozapine, and 483 ng/ml for norclozapine. Analyses of clozapine and norclozapine serum levels revealed that in a state of high levels of hepatotoxicity, serum levels for the metabolite were considerably higher than those for the parent drug, whereas the ratio of serum levels between the parent drug and its metabolite was higher for the parent drug after liver enzymes approximated normal ranges.