An observational study of Venlafaxine and CYP2D6 in clinical practice

BACKGROUND

Venlafaxine (V) is a serotonin-norepinephrine selective reuptake inhibitor, mainly metabolized by cytochrome P4502D6 (CYP2D6). CYP2D6 polymorphisms result in a variety of phenotypes: poor (PMs), intermediate (IMs), extensive (EMs), and ultrarapid metabolizers (UMs). PMs usually show poor tolerance to drugs metabolized by CYP2D6, while UMs need greater doses. The aim of this study was to evaluate the impact of CYP2D6 genotype on V dosage, therapeutic response, and side effects in a clinical outpatient setting.

METHODS

47 patients with Major Depressive Disorder, treated with V 75 - 300 mg/day, underwent CYP2D6 genotyping using the INFINITI-CYP2D6 assay. Duration of treatment and clinical outcome (Clinical Global Impression [CGI] effectiveness index) were assessed.

RESULTS

CGI assessment was performed after 6 weeks, 6 months, and 1 year of treatment with a V median dose of 150 mg/day. CYP2D6 genotyping resulted in 1 PM, 3 IMs, 42 EMs, and 1 UM. The UM took the greatest V dose (375 mg) without side effects; IMs/PMs took moderate/high doses of V (150 - 300 mg) without adverse effects; EMs displayed high response variability.

CONCLUSIONS

PM/IM patients responded to V differently than expected according to genotype. However, the UM patient responded to a dosage higher than the usual therapeutic range and without developing side effects, suggesting an association between CYP2D6 gene duplication and the therapeutic efficacy of venlafaxine. The CYP2D6 genotyping may thus provide clinicians with a potential explanation for those patients requiring greater doses of CYP2D6 substrates in order to obtain the same therapeutic efficacy.

Side effects associated with ultrarapid cytochrome P450 2D6 genotype among women with early stage breast cancer treated with tamoxifen

BACKGROUND

The side effects of tamoxifen, a drug widely used for the treatment and the prevention of recurrence in patients with estrogen receptor positive breast cancers (ER+), have been reported in clinical trials, but to date no information is available on their possible association with an increased enzymatic activity of CYP2D6 (ultra-metabolizers, UMs). The aim of this study was therefore to evaluate the association between the presence of multiple functional CYP2D6 alleles and the occurrence of side effects.

METHODS

61 women with ER+ breast cancer receiving tamoxifen monotherapy were investigated in order to assess the relationships between CYP2D6 UM phenotype and side effects. Genotyping of 16 CYP2D6 polymorphisms was performed using a new DNA microarray technology.

RESULTS

A highly significant difference was detected (41.2% of difference, 95% CI 6 - 61%, Fisher's exact test, p = 0.030) between the numbers of Ultrarapid Metabolizer patients (UM; high activity) with two or more adverse drug reactions to tamoxifen (7/9; 77.8%), compared to the number of Extensive Metabolizers (EM; normal activity), Intermediate Metabolizers (IM; reduced activity), and Poor Metabolizers (PM; no activity) with at least two side effects (19/52, 36.5%). A similar difference was also observed comparing the two groups (UM vs EM-IM-PM) for the number of side effects (median and inter quartile range, IQR: AM/EM/IM 1, IQR 0-2 vs. ULTRA 2, IQR 2-4; Mann-Whitney p = 0.005).

CONCLUSIONS

Our results suggest a new association between CYP2D6 gene duplication and side effects to tamoxifen, indicating a possible role of CYP2D6 in their occurrence.

Estimating the cost of redundancy in molecular diagnostics: the case of activated protein C resistance and factor V Leiden

BACKGROUND

The activated protein C resistance--sensitivity ratio in the presence of Factor V deficient plasma (APC-SR/Factor V) exhibits a high sensitivity for factor V Leiden mutation and has been proposed as the diagnostic approach of choice, as an alternative to genetic tests, to evaluate activated protein C resistance. A survey, including 4969 requests, was performed on the activity of a typical Molecular Diagnostics Laboratory in order to estimate the costs due to reagents, instrumentation and personnel.

METHODS

The global costs of three hypothetical diagnostic approaches were compared: (A) exclusive molecular test for FV Leiden; (B) APC-SR alone; (C) APC-SR and the exclusive confirmation of positive results with molecular test.

RESULTS

The global cost for each patient with the three approaches investigated were respectively 42.20 euros (A), 1.09 euros (B), and 433 euros (C). The cost for finding a patient with factor V Leiden mutation was 549.00 euros for A, 14.18 euros for B, and 56.32 euros for C. It was calculated that a decrease of 97.42% and 89.74% can be obtained using the approaches B and C, respectively. The difference in cost between B and C can be justified by the avoidance of false positive cases (6%) and by the impossibility of distinguishing homozygous from heterozygous patients using APC-SR exclusively (B).

CONCLUSIONS

In the case of suspected phenotype APC resistance, we suggest a laboratory approach, which provides the combined and sequential use of ProCGlobal/FV analysis and a subsequent genetic test for positive patients.