Clinical applications of pharmacogenomics guided warfarin dosing

Warfarin anticoagulant therapy: a Southern Italy pharmacogenetics-based dosing model

Background and Aim

Warfarin is the most frequently prescribed anticoagulant worldwide. However, warfarin therapy is associated with a high risk of bleeding and thromboembolic events because of a large interindividual dose-response variability. We investigated the effect of genetic and non genetic factors on warfarin dosage in a South Italian population in the attempt to setup an algorithm easily applicable in the clinical practice.

Materials and Methods

A total of 266 patients from Southern Italy affected by cardiovascular diseases were enrolled and their clinical and anamnestic data recorded. All patients were genotyped for CYP2C9*2,*3, CYP4F2*3, VKORC1 -1639 G>A by the TaqMan assay and for variants VKORC1 1173 C>T and VKORC1 3730 G>A by denaturing high performance liquid chromatography and direct sequencing. The effect of genetic and not genetic factors on warfarin dose variability was tested by multiple linear regression analysis, and an algorithm based on our data was established and then validated by the Jackknife procedure.

Results

Warfarin dose variability was influenced, in decreasing order, by VKORC1-1639 G>A (29.7%), CYP2C9*3 (11.8%), age (8.5%), CYP2C9*2 (3.5%), gender (2.0%) and lastly CYP4F2*3 (1.7%); VKORC1 1173 C>T and VKORC1 3730 G>A exerted a slight effect (<1% each). Taken together, these factors accounted for 58.4% of the warfarin dose variability in our population. Data obtained with our algorithm significantly correlated with those predicted by the two online algorithms: Warfarin dosing and Pharmgkb (p<0.001; R² = 0.805 and p<0.001; R² = 0.773, respectively).

Conclusions

Our algorithm, which is based on six polymorphisms, age and gender, is user-friendly and its application in clinical practice could improve the personalized management of patients undergoing warfarin therapy.

From sample to PCR product in under 45 minutes: a polymeric integrated microdevice for clinical and forensic DNA analysis

The extraction and amplification of DNA from biological samples is laborious and time-consuming, requiring numerous instruments and sample handling steps. An integrated, single-use, poly(methyl methacrylate) (PMMA) microdevice for DNA extraction and amplification would benefit clinical and forensic communities, providing a completely closed system with rapid sample-in-PCR-product-out capability. Here, we show the design and simple flow control required for enzyme-based DNA preparation and PCR from buccal swabs or liquid whole blood samples with an ~5-fold reduction in time. A swab containing cells or DNA could be loaded into a novel receptacle together with the DNA liberation reagents, heated using an infrared heating system, mixed with PCR reagents for one of three different target sets under syringe-driven flow, and thermally-cycled in less than 45 min, an ~6-fold reduction in analysis time as compared to conventional methods. The 4 : 1 PCR reagents : DNA ratio required to provide the correct final concentration of all PCR components for effective amplification was verified using image analysis of colored dyes in the PCR chamber. Novel single-actuation, 'normally-open' adhesive valves were shown to effectively seal the PCR chamber during thermal cycling, preventing air bubble expansion. The effectiveness of the device was demonstrated using three target sets: the sex-typing gene Amelogenin, co-amplification of the β-globin and gelsolin genes, and the amplification of 15 short tandem repeat (STR) loci plus Amelogenin. The use of the integrated microdevice was expanded to the analysis of liquid blood samples which, when incubated with the DNA liberation reagents, form a brown precipitate that inhibits PCR. A simple centrifugation of the integrated microchips (on a custom centrifuge), mobilized the precipitate away from the microchannel entrance, improving amplification of the β-globin and gelsolin gene fragments by ~6-fold. This plastic integrated microdevice represents a microfluidic platform with potential for evolution into point-of-care prototypes for application to both clinical and forensic analyses, providing a 5-fold reduction from conventional analysis time.

Pharmacogenetic testing affects choice of therapy among women considering tamoxifen treatment

Background

Pharmacogenetic testing holds major promise in allowing physicians to tailor therapy to patients based on genotype. However, there is little data on the impact of pharmacogenetic test results on patient and clinician choice of therapy. CYP2D6 testing among tamoxifen users offers a potential test case of the use of pharmacogenetic testing in the clinic. We evaluated the effect of CYP2D6 testing in clinical practice to determine whether genotype results affected choice of hormone therapy in a prospective cohort study.

Methods

Women planning to take or currently taking tamoxifen were considered eligible. Participants were enrolled in an informational session that reviewed the results of studies of CYP2D6 genotype on breast cancer recurrence. CYP2D6 genotyping was offered to participants using the AmpliChip CYP450 Test. Women were classified as either poor, intermediate, extensive or ultra-rapid metabolizers. Results were provided to clinicians without specific treatment recommendations. Follow-up was performed with a structured phone interview 3 to 6 months after testing to evaluate changes in medication.

Results

A total of 245 women were tested and 235 completed the follow-up survey. Six of 13 (46%) women classified as poor metabolizers reported changing treatment compared with 11 of 218 (5%) classified as intermediate, extensive or ultra-rapid metabolizers (P < 0.001). There was no difference in treatment choices between women classified as intermediate and extensive metabolizers. In multi-variate models that adjusted for age, race/ethnicity, educational status, method of referral into the study, prior knowledge of CYP2D6 testing, the patients' CYP2D6 genotype was the only significant factor that predicted a change in therapy (odds ratio 22.8; 95% confidence interval 5.2 to 98.8). Genetic testing did not affect use of co-medications that interact with CYP2D6.

Conclusions

CYP2D6 genotype testing led to changes in therapy among poor metabolizers, even in the absence of definitive data that an alternative medicine improved outcomes. Pharmacogenetic testing can affect choice of therapy, even in the absence of definitive data on clinical impact.