Recent studies indicate that persons experiencing their first episode of acute symptoms of schizophrenia respond as well or better to antipsychotic medications in terms of symptom reduction than persons experiencing a recurrent episode. They may also respond to somewhat lower doses. They also carry a significant side-effect burden. Rapid initiation of antipsychotic treatment is important at the onset of an exacerbation, but not a rapid loading dose. As above, studies have found no superior efficacy of any of the antipsychotic medications relative to each other in the treatment of positive symptoms.
Plasma levels are most useful when using haloperidol, which has only one active metabolite.
In general, there is at best a moderate correspondence between plasma drug level and clinical response to antipsychotic medications. Studies suggest an inverted-U or therapeutic window response curve such that persons with moderate plasma levels of haloperidol show a better clinical response than those with low or high levels. The upper end of this therapeutic window is often defined by side effects. Inadequate clinical response to apparently adequate dosages of antipsychotic medications warrants assessment of plasma levels to rule out unusual or altered drug metabolism or noncompliance. The effectiveness of and continued need for anti-Parkinson agents should be assessed in an ongoing fashion.