Quetiapine and norquetiapine serum concentrations and clinical effects in depressed patients under augmentation therapy with quetiapine.

BACKGROUND: Quetiapine has been recently approved as an add-on therapy in the treatment of major depressive disorders in the case of inadequate response to antidepressant monotherapy. Thereby the antidepressant potential is attributed to the N-demethylated metabolite norquetiapine (NQ). The aim of this cross-sectional analysis was to relate quetiapine (Q) doses to serum concentrations of Q and its active metabolite and clinical effects. METHODS: Data were obtained from patients who had been treated with different antidepressants and augmented under naturalistic conditions with Q for whom blood level measurements were requested. RESULTS: For this analysis, 105 depressed patients were included who had been augmented with Q. The mean daily doses of Q were 222 ± 125 mg. Doses correlated significantly (P < 0.001) with the highly variable serum concentrations of both Q and NQ. Median serum concentrations of Q and NQ were 46 ng/mL (25th to 75th percentile 20-91 ng/mL) and 59 ng/mL (25th to 75th percentile 26-133 ng/mL), respectively. Concentrations per dose ranged from 0.10 to 0.58 ng·ml·mg for Q and from 0.17 to 0.59 ng·ml·mg for NQ. Most patients (55%) received comedications in addition to the antidepressant drug and Q. According to the clinical global impressions scale, 60% of the patients were either much (36%) or very much improved (24%). Receiver-operating characteristic analysis revealed no significant differences of serum concentrations between responders and nonresponders for NQ (P = 0.835) but a trend for Q (P = 0.056). CONCLUSIONS: Due to marked variability of Q and NQ concentrations in the blood, therapeutic drug monitoring may be helpful to identify pharmacokinetic peculiarities. The lack of correlation between serum concentrations of NQ and clinical improvement casts doubts on the concept that NQ is the pharmacologically active principle for the augmentation therapy.

Severe tremor after cotrimoxazole-induced elevation of venlafaxine serum concentrations in a patient with major depressive disorder.

: We describe a female patient who was an extensive metabolizer of cytochrome P450 isoenzyme (CYP) 2D6 and an intermediate metabolizer of CYP2C19 (genotype: CYP2C19 *1/*2). She exhibited high serum concentrations of venlafaxine and O-desmethylvenlafaxine and developed severe tremor after comedication with cotrimoxazole (sulfamethazole/trimethoprim). Venlafaxine is mainly metabolized by O- and N-demethylation. O-demethylation is catalyzed by the highly polymorphic CYP2D6 and N-demethylation by several enzymes, CYP2C19, CYP2C9, and CYP3A4. The observed overall pharmacokinetic effect was most probably the result of decreased N-demethylation of venlafaxine by (1) reduced expression of CYP2C19 due to a genetic deficit and (2) inhibition of CYP2C9 by cotrimoxazole.

Potential cost-effectiveness of therapeutic drug monitoring for depressed patients treated with citalopram.

BACKGROUND: For patients treated with citalopram, it was recently shown that serum concentrations above 50 ng/mL on day 7 of treatment are associated with an improved therapeutic outcome. The aim of this post hoc analysis was to calculate a potential cost-effectiveness of therapeutic drug monitoring (TDM) considering costs for hospitalization, medication, and drug analysis. METHODS: The study included patients with major depression. Weekly measurements of serum concentrations and assessments of psychopathology were conducted. RESULTS: Fifty-five patients were included in this analysis. For patients with high citalopram serum concentrations (>50 ng/mL), the mean duration of hospitalization was 49 ± 20 days, and it was 72 ± 37 days (P = 0.03) in the group with low drug concentrations (<50 ng/mL). Considering daily costs for hospitalization of 250€,;, the potential savings amounted to 5750€,; per patient for the 23 days. Assuming that 11% of the variation of duration of hospitalization per patient were attributed to the serum concentration of the drug, the resulting savings were 633€,; per patient. Considering the officially listed price of 21€,; per TDM assay, total costs for weekly measurements over a period of 10 weeks of hospitalization were 210€,;. In the groups with high and low serum concentrations, daily costs for citalopram medication were 3.00 ± 0.80€,; and 2.42 ± 0.70€,;, respectively (P = 0.002), and the mean number of comedications was nearly identical, that is, 1.87 ± 1.74 and 1.81 ± 1.86 drugs, respectively (P = 0.919). CONCLUSIONS: The data taken together indicate that TDM-guided dosing of citalopram has the potential to be cost effective by reducing the length of hospitalization.

Therapeutic drug monitoring for antidepressant drug treatment.

The aim of antidepressant drug treatment is to produce remission without causing adverse effects during the acute phase of the illness and to prevent relapses or recurrences during continuation or maintenance therapy. To achieve these goals, drug choice and dosage must be optimized for each patient individually. Therapeutic drug monitoring (TDM), which is based on the assumption that clinical effects correlate better with blood levels than doses, can be helpful. When using tricyclic antidepressant drugs TDM enhances safety and efficacy. For newer antidepressant drugs, however, it is a matter of debate to which extend TDM can have beneficial effects. For many antidepressants there exist carefully designed studies concerning the relationship between plasma concentration and clinical effects that allow the definition of recommended therapeutic ranges of the plasma concentration. In some drugs however, concentration-effect studies are lacking so far, but target ranges resulting from clinically relevant plasma concentrations or from pharmacokinetic studies could be provided. During the last years, knowledge on therapeutic references ranges in blood towards TDM guided treatment has markedly improved for new antidepressant drugs, and many specific indications have been defined for useful TDM. Recently published guidelines describe the best practice of TDM for neuropsychiatric drugs. The aim of this review is to summarize the current status of TDM for antidepressant drugs and discuss the literature with regard to response optimization, pharmacovigilance and economic benefits and with regard to needs for further research.

Association between citalopram serum levels and clinical improvement of patients with major depression.

Imaging studies have shown that serum concentrations of the selective serotonin reuptake inhibitor citalopram correlate with serotonin transporter (5-HTT) occupancy in vivo. In patients with major depressive disorders treated with citalopram, 80% 5-HTT occupancy was considered to be necessary for maximal therapeutic effects, which requires citalopram serum concentrations of at least 50 ng/mL. The aim of this study was to compare treatment outcome in patients with citalopram serum concentrations greater than and less than 50 ng/mL after 7 days of treatment. This study included inpatients with acute major depressive disorder according to International Classification of Disease, 10th Revision who were treated with citalopram. In weekly intervals, the severity of depression was assessed with the 17-item Hamilton Depression Rating Scale (HAMD-17), and serum concentrations of citalopram were measured from baseline until week 5. Fifty-five patients were eligible for this analysis. After 7 days of treatment, 19 patients showed citalopram serum concentrations of 50 ng/mL or greater; 36 patients had lower concentrations. Patients at greater than the 50-ng/mL threshold had (i) lower mean HAMD-17 sum scores from day 7 to end point (P ≤ 0.018 for each analysis); (ii) a more pronounced HAMD-17 decrease (P ≤ 0.019 for each analysis), and (iii) 23 days' shorter duration of hospitalization (P = 0.033) than patients with levels of citalopram less than 50 ng/mL. As regards adverse effects, both patient groups were not significantly different. Despite therapeutic doses, a significant number of patients had serum concentrations less than 50 ng/mL, and these were associated with an unfavorable treatment outcome; therapeutic drug monitoring is recommended to optimize dosing citalopram in the early phase of treatment.