Predicting Plasma Olanzapine Concentration Following a Change in Dosage: A Population Pharmacokinetic Study.

INTRODUCTION: Due to high inter-individual variability in peripheral pharmacokinetic parameters, dosing of antipsychotics currently relies on clinical trial-and-error, and predicting antipsychotic plasma concentrations before changing a dose has been a challenge. METHODS: Patients with schizophrenia receiving a stable dose of olanzapine were included. 2 plasma samples were collected at 2 given time points for the measurement of plasma olanzapine concentrations. At least 7 days after a dosage change of olanzapine, a third sample was collected. The plasma concentration of the third sample was predicted in a blinded fashion using a mixed-effects model with NONMEM(®), using the following information: the 2 baseline plasma concentrations, the interval between the last dose and blood draw, and clinical and demographic information. RESULTS: 31 subjects (mean±SD age=56.0±11.6; 19 men) were enrolled. The mean prediction (95% confidence interval) errors were 1.6 (-2.8 to 6.0) ng/mL. A highly significant correlation was observed between the observed and predicted concentrations of the third sample (r=0.91, p<0.001). DISCUSSION: Plasma olanzapine concentrations following an actual dosage change can be predicted in advance with a high degree of certainty.

Predicting age-specific dosing of antipsychotics.

Antipsychotic medications are the standard of care for both acute and maintenance treatment of schizophrenia, the latter requiring an indefinite treatment across a patient's life span. However, dosing and tolerability of antipsychotics have been studied primarily in younger patients, and very limited data are available for age- and phase-specific dosing. This leaves the clinician with no guidance on dose adjustment as patients grow older-an issue of critical importance, especially in light of recent concerns about increased morbidity and mortality associated with antipsychotics.

Effect of nortriptyline and paroxetine on extrapyramidal signs and symptoms: A prospective double-blind study in depressed elderly patients.

Selective serotonin-reuptake inhibitors (SSRIs) and tricyclic antidepressants (TCAs) have been reported to induce extrapyramidal signs and symptoms (EPS). The authors examined the change from baseline EPS, measured by an objective rating scale, in a group of elderly depressed patients participating in an ongoing randomized, double-blind comparison of nortriptyline and paroxetine. Mild baseline EPS were present in both groups. After 6 weeks of antidepressant treatment, patients in the nortriptyline group showed a significant decrease in total EPS scores. Patients in the paroxetine group showed a similar decrease in EPS from baseline, which did not reach statistical significance. There was no significant difference between nortriptyline and paroxetine in the change in EPS.

Managing antipsychotic-induced parkinsonism.

Notwithstanding the advent of clozapine and other 'atypical' antipsychotic agents, the conventional ('typical') antipsychotic agents remain in widespread use. Antipsychotic-induced parkinsonism is a highly prevalent adverse effect that may result in increased morbidity and noncompliance. Bedside examination is generally sufficient for the detection of the onset of parkinsonism and should be carried out frequently in the first 3 months of treatment. In addition to decreasing patient discomfort, monitoring for antipsychotic-induced parkinsonism also serves to identify the minimally effective dosage required for the individual patient. Several strategies are utilised in the management of antipsychotic-induced parkinsonism including dosage reduction, switching to other antipsychotic agents and the use of antiparkinsonian drugs such as anticholinergic agents and amantadine. Anticholinergic agents remain the mainstay of the pharmacological management of antipsychotic-induced parkinsonism in younger patients. Amantadine is a better tolerated agent for elderly patients, with similar efficacy to the anticholinergic agents. The routine use of prophylactic anticholinergics is not recommended and is clearly contraindicated in the elderly. An individualised risk-benefit assessment is necessary for the younger patient in whom prophylactic use of anticholinergic drugs is considered.