Determinants of pharmacodynamic trajectory of the therapeutic response to paroxetine in Japanese patients with panic disorder.

PURPOSE: The objective of this study was to evaluate genetic and pharmacokinetic factors to establish the pharmacotherapeutic effect of paroxetine (PAX) in patients with panic disorder (PD). METHOD: Subjects were 65 drug-naïve patients who fulfilled the DSM-IV-TR criteria for PD diagnosis. All subjects were administered PAX (10 mg/day) for 4 weeks, and PD severity was assessed using the Panic and Agoraphobia Scale (PAS) at baseline and at 2 and 4 weeks after initiation of treatment. Plasma PAX concentration was determined by high-performance liquid chromatography. Serotonin transporter gene-linked polymorphic region (5-HTTLPR) variants and the -1019C/G promoter polymorphism of the serotonin 1A receptor (5-HT(1A)) gene were determined by PCR analysis. RESULTS: Multiple regression analysis revealed that the plasma concentrations of PAX, 5-HTTLPR genotype, and -1019C/G 5-HT(1A) gene polymorphism were significant factors affecting clinical response to PAX (reduction ratio of PAS score) at 2 weeks after the initiation of pharmacotherapy. The -1019C/G 5-HT(1A) gene promoter polymorphism, PAS score at baseline, and adverse effects were found to be the significant factors affecting clinical response to PAX at 4 weeks after initiation of pharmacotherapy. CONCLUSION: The present study revealed that plasma concentration of PAX, 5-HTTLPR genotype, -1019C/G 5-HT(1A) genotype, PAS score at baseline, and adverse effects may influence the therapeutic response to PAX in patients with PD.

[Pharmacogenetics/pharmacogenomics in psychiatry].

Pharmacogenetics/pharmacogenomics has been developed so rapidly in these twenty years and the pharmacogenetic/pharmacogenomic research in psychiatry is also the case. Especially, the impact of genetic polymorphism (e.g., cytochrome P450 (CYP)) on pharmacokinetics of psychotropics have been extensively studied, however, recently, most of the studies in this field have been moved to pharmacodynamic study, i.e., the studies on impact of genetics polymorphism on clinical response and adverse effects to pharmacotherapy with psychotropics. Development of pharmacogenetics/ pharmacogenomics in psychiatry may well lead to a future of individualized pharmacotherapy for psychiatric disorders.

Genetic and pharmacokinetic factors affecting the initial pharmacotherapeutic effect of paroxetine in Japanese patients with panic disorder.

OBJECTIVE: The objective of this study was to evaluate genetic and pharmacokinetic factors affecting the initial pharmacotherapeutic effect of paroxetine (PAX) in Japanese patients with panic disorder (PD). METHOD: Plasma concentration of PAX was determined by high performance liquid chromatography. Serotonin transporter gene-linked polymorphic region (5-HTTLPR) variants were determined by polymerase chain reaction techniques. PD severity was assessed using the Panic and Agoraphobia Scale (PAS). RESULTS: Multiple regression analysis revealed that the plasma concentration of PAX, 5-HTTLPR genotype, and comorbid physical illness were significant factors affecting the initial pharmacotherapeutic effect of PAX in PD and indicated that these factors accounted for 52.4% (R(2) = 0.524) of the variability in the percent reduction in PAS score. The final model was described by the following equation (P = 0.001): percent reduction in PAS score (%) = 68.5 - 1.2 x [plasma concentration of PAX (ng/ml)] - 33.0 x (L/S = 1, S/S = 0) - 21.8 x (with comorbid physical illness = 1, without comorbid physical illness = 0). CONCLUSION: The high plasma concentration of PAX, the L/S genotype of 5-HTTLPR, and comorbid physical illness might be associated with a poor response to the initial phase of pharmacotherapy of PD with PAX.

High plasma concentrations of paroxetine impede clinical response in patients with panic disorder.

Selective serotonin reuptake inhibitors are thought to interact with serotonergic neurons and be effective for treatment of panic disorder. In the present study, the authors investigated an association between plasma concentrations of paroxetine in patients with panic disorder and clinical response to initial treatment with paroxetine. Subjects were 21 unrelated Japanese patients who fulfilled DSM-IV-TR criteria for a diagnosis of panic disorder (6 males, 15 females, mean age 35.9 +/- 11.3 years). Subjects were administered 10 mg/day of paroxetine for 2 weeks as initial treatment. Improvement of the symptoms of the disorder was assessed with the Panic and Agoraphobia Scale (PAS). In the range of plasma levels >20 ng/mL, none of the subjects showed the reduction ratio in PAS score >0.2. The subjects whose plasma concentrations of paroxetine were less than 20 ng/mL had a significantly higher mean reduction ratio in PAS score than the subjects whose plasma concentrations of paroxetine were >20 ng/mL. Multiple regression analysis showed that the plasma concentration of paroxetine was the only significant factor and accounted for 28.0% of the variability in the reduction ratio of PAS score of the subjects. The final model of correlation was: reduction ratio in PAS score = 0.423 - 0.009 x (plasma concentrations of paroxetine) (R = 0.529, P = 0.014, coefficient of determination (R2) = 0.280). Assuming that the reduction ratio in PAS score was 0.2 in the equation above, plasma concentration of paroxetine is calculated to be about 25 ng/mL, which is suggested to be the upper end of the therapeutic window for the initial phase of the treatment with paroxetine for panic disorder.