Citalopram is a selective serotonin reuptake inhibitor (SSRI) mainly prescribed to treat major depression.

The aim of this study was to compare the pharmacokinetic characteristics of a new and a branded citalopram 20 mg formulation to support the marketing authorization of the test formulation in China.

A single-dose, open-label, randomized-sequence, two-period crossover design was used in this study. Healthy Chinese male cytochrome P450 (CYP) 2C19 extensive metabolizers, aged 18–40 years, were eligible to participate. CYP2C19 poor metabolizers were excluded, based on genotyping of genomic DNA from blood samples. Twenty-four subjects were randomly assigned to receive the test formulation followed by the reference formulation, and then vice versa. A 2-week washout occurred between study periods. Blood samples were collected for up to 144 h post-dose. Quantification was carried out using a validated high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) method. Pharmacokinetic parameters were calculated and analysed statistically. The two formulations were considered pharmacokinetically equivalent if the 90 % confidence intervals (CIs) of the log-transformed ratios (test/reference) of the maximum plasma concentration (C_max), area under the plasma concentration-time curve from time zero to the last measurable concentration (AUC_last), and area under the plasma concentration-time curve from time zero to infinity (AUC_∞) were within the predetermined acceptance range (70–143 % for C_max; 80–125 % for AUC_last and AUC_∞) according to China State Food and Drug Administration bioequivalence guidelines. Tolerability was monitored by clinical assessment, vital signs, laboratory analysis and interviews with participants about adverse events.

A total of 24 participants, with a mean (SD) age of 26 (3) years (range 22–32 years), body weight of 65.2 (5.0) kg (range 53–73 kg), and height of 172.7 (4.9) cm (range 159–182 cm), were enrolled in this study. Both formulations showed similar pharmacokinetic profiles. Mean (SD) AUC_last, AUC_∞ and C_max were 1436 (341) ng · h/mL, 1595 (381) ng · h/mL and 32.3 (5.9) ng/mL, respectively, for the test formulation, and 1444 (388) ng · h/mL, 1648 (504) ng · h/mL, 33.1 (7.4) ng/mL, respectively, for the reference formulation. Median (range) time to reach C_max (t_max) was 2 (1–12) hours (test) and 3 (1–6) hours (reference). The 90 % CIs of the treatment ratios for the ln-transformed values of C_max, AUC_last and AUC_∞ were 92.5–103.6, 95.2–100.6 and 96.4–105.4, respectively. No significant difference was found between treatments with regard to pharmacokinetic parameters. Fifteen adverse events were reported during the study but none were considered serious.

This single-dose study found that the test and reference citalopram 20 mg tablets met the regulatory criteria for assuming bioequivalence in the selected healthy Chinese male subjects. Both formulations were well tolerated.