The influence of ethnicity and antidepressant pharmacogenetics in the treatment of depression

Antidepressant disposition can be influenced by a variety of CYP isozymes and their effects in the treatment of depression are reviewed. The CYP isozymes 2D6, 3A4, 1A2 and 2C are discussed in regard to antidepressant drug pharmacokinetics, clinical relevance and variability in activity for each isozyme. Polymorphism has been identified with CYP 2D6 and 2C19. Disposition of antidepressants which are substrates of these two isozymes can also be influenced and contributes towards the wide interpatient and interethnic variability found with these drugs. Antidepressants (especially SSRIs) can be CYP isozyme inhibitors and produce significant drug-drug interactions.

Dextromethorphan phenotyping and haloperidol disposition in schizophrenic patients

This study examined the relationship between the metabolic ratios of dextromethorphan/dextrorphan, haloperidol disposition, and the incidence of extrapyramidal side effects in schizophrenic patients. Eighteen schizophrenic patients were phenotyped with a test dose of dextromethorphan prior to the initiation of haloperidol treatment. The metabolic ratio of dextromethorphan/dextrorphan was determined in each patient. Patients were treated with oral haloperidol 10 mg/day for 2 weeks. Blood samples for haloperidol and reduced haloperidol were obtained at week 2 of haloperidol treatment. Haloperidol and reduced haloperidol plasma concentrations were assayed by HPLC with electrochemical detection. Significant correlations of dextromethorphan/dextrorphan metabolic ratios vs. plasma haloperidol concentrations, reduced haloperidol concentrations, and reduced haloperidol/haloperidol ratios were found (r = 0.726, P = 0.0007; r = 0.782, P = 0.0001; and r = 0.619, P = 0.006, respectively). Ten patients who experienced extrapyramidal side effects had higher reduced haloperidol concentrations and reduced haloperidol/haloperidol ratios than the other patients (2.49 +/- 1.42 [S.D.] ng/ml vs. 1.10 +/- 0.46 ng/ml, P = 0.014 and 0.287 +/- 0.102 vs. 0.192 +/- 0.065, P = 0.030). The former also had a trend to have higher haloperidol concentrations and dextromethorphan/dextrorphan ratios than the latter (8.04 +/- 2.91 ng/ml vs. 5.83 +/- 1.79 ng/ml, P = 0.066 and 0.023 +/- 0.017 vs. 0.011 +/- 0.010, P = 0.077). Phenotyping patients has the potential to assist clinicians in predicting plasma drug concentrations during the subsequent neuroleptic drug treatment. Further research with phenotyping and psychotropic drug metabolism in psychiatric patients is needed.