Relationship between mirtazapine dose, plasma concentration, response, and side effects in clinical practice.

OBJECTIVE: The aim of this study was to evaluate the benefit of mirtazapine plasma concentration monitoring in a typical clinical setting. METHODS: The relationship between mirtazapine plasma concentration, dose, response, and side effects was studied in 65 inpatients presenting with a depressive episode according to ICD-10. Plasma concentrations, the 17-item Hamilton Depression Rating (HAMD), and the UKU side effect rating were performed weekly. A subgroup of 45 patients was evaluated for a concentration-response relationship. RESULTS: We found a low positive correlation between plasma concentration and dose. A low negative correlation between plasma concentration and increased duration of sleep was noted in the first week of mirtazapine treatment, but not during the entire observation time. Responders to mirtazapine treatment presented with higher plasma concentrations than non-responders, revealing a threshold concentration of 30 ng/mL. CONCLUSION: The mirtazapine dose is a weak predictor of mirtazapine plasma concentrations. Plasma concentration measurements may therefore be useful to adjust mirtazapine doses in non-responders with plasma concentrations below 30 ng/mL. Sedative effects appear temporary and require no plasma concentration control when standard doses are administered.

Therapeutic drug monitoring of tricyclic antidepressants: how does it work under clinical conditions?

Therapeutic drug monitoring (TDM) of tricyclic antidepressants (TCA) is established in the treatment of depression to optimize outcome and safety. However, there are few reports on TDM under naturalistic clinical conditions. In the present study, we investigated a TDM group (TDM) and a randomly assigned parallel group without TDM (no-TDM) while on TCA treatment. Serum levels were analyzed in both cohorts, but feedback and dose recommendation were only provided for the TDM group. Serum levels of TCA were assessed by high-performance liquid chromatography (HPLC). The outcome was measured weekly using the Hamilton Depression Rating Scale (HAMD), the Clinical Global Impressions Scale (CGI), and the UKU side-effect scale. 84 patients with depressive disorder according to DSM-IV were recruited in three centers (TDM, n = 43; no-TDM, n = 41; mean age 49.9 +/- 13.2 years, 63.1 % female). Patients were treated with either amitriptyline (n = 69) or doxepin (n = 15); the mean dosage at endpoint was 126 +/- 35 mg and 155 +/- 47 mg, respectively. The mean study duration was 21 +/- 8 days. Both groups improved according to HAMD (from 25.2 +/- 8.4 at baseline to 12.0 +/- 7.4 at endpoint) and CGI scores (68 % responders). Moderately severe or severe side effects occurred in 16 % of patients. Adequate dose adjustment was significantly higher in the TDM group (60 % vs. 46 %, p < 0.05); this led to a significantly higher rate of therapeutic serum levels in the TDM group (58 % vs. 44 %, p < 0.05). Direct effects of TDM were not found for effectiveness. Therapeutic TCA serum levels over weeks one to three, however, were associated with significantly better outcome at endpoint (p < 0.05) as measured with changes in the HAMD or CGI response rates from baseline to endpoint. Finally, considerable side effects occurred significantly more often when serum levels were above the therapeutic range (27 % vs. 11 %; p < 0.01). We conclude that treating depression with TCA can be optimized by early TDM, which is superior to clinical judgment on its own. Since the psychiatrists in charge were less than completely "compliant" to the recommendations provided together with serum levels, the effect could be more pronounced than this study shows. The results encourage further studies in order to optimize antidepressant pharmacotherapy when using TDM appropriately.

[Olanzapine: pharmacology, pharmacokinetics and therapeutic drug monitoring]. / Olanzapin: Pharmakologie, Pharmakokinetik und Therapeutisches Drug Monitoring.

Olanzapine is an effective and safe antipsychotic drug. Its pharmacokinetic properties are comparable to those of classical antipsychotics. Oxidative processes are mediated by the cytochrome P450 isoenzyme CYP1A2 and to a minor degree by CYP2D6. Olanzapine's main route of metabolism is by glucuronidation. Therapeutic doses result in a wide variability of serum levels; dose and serum concentration are linearly correlated. Smoking and carbamazepine induce cytochrome P450 isoenzymes and thus decrease olanzapine serum levels. Inhibition of CYP1A2 by fluvoxamine yields increased concentrations; however, clinically relevant CYP2D6 inhibition was observed only in combination with additional disposition factors, such as female gender or old age. As a rule dose adjustment is not necessary but moderate renal or hepatic impairment calls for control of serum levels to provide maximal safety during olanzapine therapy. Therapeutic drug monitoring (TDM) and toxicology studies are carried out by HPLC methods using UV or MS detection. The optimal therapeutic range of olanzapine serum levels is 20 to 40 ng/ml. Concentrations of 80 ng/ml are considered threshold for the occurrence of adverse events; however, toxicological studies showed that postmortem plasma levels are higher than antemortem levels. Lethality of high olanzapine was only observed in combination with other drugs. Moderate increases of prolactin levels were detected during administration of olanzapine. In relation to olanzapine therapy, several case reports of neutropenia and agranulocytosis appeared in the literature. Weight gain in olanzapine-treated patients does not correlate with serum levels. Olanzapine response is augmented when patients' serum levels are titrated to 20 to 40 ng/ml thereby minimizing the occurrence of side effects, thus TDM is recommended for patients treated with olanzapine.