Psychopharmacology (2011) 215:321–332 crossover sequences. Subjects received one tablet of dextromethorphan 30 mg together with 200 ml water before bedtime. Subjects had to empty their bladder pre-dose. Subsequently, subjects' morning urine was collected in containers. The excretion ratio dextromethorphan/dextro- rphan in urine determined the CYP2D6 metabolizer status of each subject. Subjects with an excretion ratio ≥0.3 were characterized as poor metabolizers, subject whose excretion ratio <0.3 were characterized as extensive metabolizers. In total, 7 (22%) subjects were classified as poor metabolizers (4 males/3 females) and 25 (78%) subjects (12 males/13 females) as extensive metabolizers. Pharmacokinetics Blood samples (5 ml) for esmirtazapine determinations were collected at the time points indicated in Fig. 1 and processed to plasma. Plasma samples were stored and frozen at −20°C and later analyzed by LC-MS-MS. The lower limit of quantification is 0.02 ng/ml. Statistics Sample size was based on a power calculation for non- inferiority between esmirtazapine 4.5 mg and placebo after multiple-dose administration with respect to actual driving performance as assessed by means of SDLP. Given a mean population standard deviation of 4.0 cm, a mean difference in SDLP of 0.5 cm between multiple dose esmirtazapine 4.5 mg and placebo, a test–retest ≥0.70 and a non- inferiority margin of 2.5 cm, a sample size of 26 subjects is sufficient to demonstrate non-inferiority with a power of at least 90% and a two-sided α-level of 0.05. This sample size is also sufficiently large (i.e., power of at least 90%) for detecting a clinically relevant effect of 2.5-cm mean difference in SDLP between single-dose zopiclone 7.5 mg and placebo to demonstrate assay-sensitivity. Taking into account the possibility of drop-outs the total sample size was set at N= 32 or 8 subjects per treatment crossover sequence stratified by gender (i.e., four males and four females). Estimation of differences in SDLP between poor and extensive CYP 2D6 metabolizers was not pre-specified as an objective of this study, and hence, the study was not powered for these subgroup analyses. Therefore, the results of these subgroups have to be interpreted in the perspective of the explorative character of these analyses. Statistical analyses of the driving, cognition, and psycho- motor function parameters was done using a mixed model including fixed factors for treatment, period, treatment sequence, gender, day, and treatment by day interaction. Kenward–Roger approximation was used to estimate denom- inator degrees of freedom. Subject was included as a random 325 factor and day as a repeated factor. No fixed structure was assumed for the repeated measures (co)variance. Least-squares estimates of contrasts to placebo and two-sided 95% CI were obtained from this model for single-doses and multiple-doses treatment separately. Efficacy analyses included all subjects randomly assigned to treatment sequence, treated, for whom results from at least one driving test during treatment was available, and without any pre-defined protocol violations that might impact efficacy conclusions. Adverse events (AEs) were coded using the MedDRA dictionary. AEs occurring during the washout period were assigned to the treatment taken during the preceding treatment period. AEs occurring before intake of zopiclone 7.5 mg in the placebo-zopiclone treatment period were assigned to placebo. AE tabulations included the number and percentage of subjects with at least one AE by MedDRA preferred term. Safety analyses included all subjects that were randomly assigned to treatment sequence and treated. For the efficacy evaluation, all complete and incomplete data were included in the statistical analyses (i.e. no imputation was performed for missing data). Statistical analyses were per- formed using SAS® version 9.1.3. The aim of the present study was to compare next-day driving performance, as expressed by the SDLP, of esmirtazapine with placebo. The study was designed as a non-inferiority trial, with evaluation of SDLP effects in relation to a reference BAC concentration. For SDLP, non- inferiority between treatments was concluded if the upper limit of the two-sided 95% confidence interval (CI) of the mean difference in SDLP between drug and placebo below 2.5 cm. The upper limit of the non-inferiority margin is chosen such that it excludes with high certainty a drug effect >BAC 0.5 mg/ml, which is considered clinically relevant. Results A total of 32 subjects entered the study. Twenty-nine subjects completed all four treatment periods whereas, three subjects prematurely discontinued. Two subjects dropped out during treatment with esmirtazapine 4.5 mg due to adverse events. In one case, the subject complained of asthenia, fatigue, and muscular weakness starting 25 min after intake of the first dose and decided to stop study participation. This subject was a poor CYP 2D6 metabo- lizer and the adverse events were considered related to study treatment. The other subject was discontinued after being diagnosed with breast cancer. In the judgment of the medical supervisor, this serious adverse event was not likely to be related to study treatments. Another subject dropped out between the third and fourth treatment period because she could no longer adhere to study restrictions relating to alcohol intake. Median compliance to trial