Implementation of pharmacogenetics in a clozapine treatment resistant patient: a case report.

We report the case of a young Caucasian male with disorganized chronic schizophrenia, an active smoker and nonresponder to 400 mg of clozapine/day. Therapeutic clozapine monitoring was analyzed revealing a low clozapine:norclozapine ratio. An additional pharmacogenetic test was carried out showing that the patient carried variant ( gene), which has been associated with nonresponse to clozapine in smoker patients. A genetic variation in the gene was also found, which could be related to the poor response to clozapine. The remainder of the genes analyzed (, and ) were not directly associated with the patient's phenotype. The dose of clozapine was increased to 600 mg/day, reaching the therapeutic range. This case shows how pharmacogenetics can help in understanding the value of plasma levels to provide clinical improvement.