In addition, the effects of drug noncompliance and EPS can both mimic true treatment resistance.137,138 At least a 1- to 2-year course of persistent symptoms should also be considered as one of the criteria for treatment BYL719 resistance in schizophrenia,

because of the waxing and waning course of this illness. The most widely accepted current criteria for treatment resistance in schizophrenia were first used by Kane et al.127 These criteria, modified for clinical use, are as follows: Persistent positive psychotic symptoms (item score ≥ 4) on Inhibitors,research,lifescience,medical at least two of four positive symptom items on the BPRS: hallucinatory behavior, suspiciousness, unusual thought content, or conceptual disorganization. Current presence of at least a moderately severe illness as rated by the total BPRS (score ≥45 on the 18item scale) and a score of ≥4 on the Clinical Global

Impression (CGI) scale. Persistence of illness: no period of good social and/or occupational functioning within the last Inhibitors,research,lifescience,medical 5 years. Drug-refractory condition defined as at least two periods of treatment in the preceding 5 years with appropriate doses of conventional or SGAs, each without clinically significant symptom relief. The rates for two retrospective drug trial failures have been found Inhibitors,research,lifescience,medical to be similar to the rates for three when screening for treatment resistance; this fact is now widely accepted.138 People Inhibitors,research,lifescience,medical not responsive to two adequate antipsychotic trials (one retrospective and one prospective) have less than a 7% chance of responding to another trial.139 The Food and Drug Administration (FDA) guidelines for clozapine, as reflected in the product labeling for clozapine,140 also states that people should fail to respond to two separate trials of antipsychotics, before being treated with clozapine. It is generally recognized that Inhibitors,research,lifescience,medical a 4- to 6-week period (rather than strictly a 6-wcck one) is adequate for a treatment trial of an antipsychotic.141 Dosages of >400 mg/day of chlorpromazine

have been shown to be adequate to block 80% to 90% of dopamine receptors (thought to be the target of this drug action).142 Higher doses produce no direct therapeutic benefit, even in patients not Thiamine-diphosphate kinase responsive to therapy, and do not have greater efficacy in acute treatment than lower doses.143-145 Therefore, two 4- to 6-weck trials of 400 to 600 mg/day chlorpromazine or a chlorpromazine equivalent are now accepted as a standard for an adequate trial.138,146 Until the arrival of standardized criteria for defining treatment resistance, research into the neurobiological nature of the problem had been scant.147 Recently, however, with the use of more objective criteria, some consistent findings have been seen. There is a relative paucity of data in this area and more research needs to be done.