A Genomic Approach to Warfarin Dose Prescription in Admixed Caribbean Hispanics

Despite the substantial number of work published over the past years in different populations around the world, a fundamental gap remains in understanding whether and how genomic admixture and polymorphisms in warfarin-related pharmacogenes account for the high inter-individual dose variability observed in Caribbean Hispanic patients. In addition to being a medically underserved population, often marginally represented in clinical studies, Caribbean Hispanics are also a genomically heterogeneous population whose high level of admixture has produced a rich repertoire of combinatorial genotypes (e.g., CYP2C9*2/*5 + VKORC1-1639 A/A) that appear to challenge current pharmacogenetic-driven prescribing models. Our project takes a novel approach to definitively assess this admixture component and is also highly practical for its incorporation into a customized pharmacogenetic algorithm that will be implemented in "real-world" clinical settings through a web-based portal. Moreover, the project is also aimed at performing DNA-sequencing to identify those unknown variants on candidate pharmacogenes (i.e., CYP2C9 and VKORC1) that may contribute further to explain dose variability in Caribbean Hispanics. Shaped by strong preliminary data from a SC2 pilot project, the investigators will assess clinical validity and utility of an admixture-adjusted, pharmacogenetic-guided prescribing model for personalized prediction of effective warfarin dosing in Caribbean Hispanics, which also encompasses genetic (common and novel variants) and non-genetic clinical and demographic factors. The study will be conducted over 4 years in 300 patients with thromboembolic disorders receiving warfarin. Four collaborating/recruiting sites will be further connected through precise delivery of genotyping results and prescribing advice to clinicians via a web-based portal. Our novel assessment of genetic admixture will quantify the contribution of European, African and Amerindian ancestry, and the investigators will test whether this admixture component can explain the heritability that is currently missing in the response variability to this drug among Caribbean Hispanics. If successful in our target population, the same approach can ultimately render current pharmacogenomic models for clinical management of related thromboembolic conditions more accurate and predictive for other populations.

The proposed research will advance and expand our understanding of how these clinically relevant variants affect the response to warfarin in an admixed population. Advancing knowledge in the important and under-investigated area of pharmacogenetics in minority populations will generate results that apply to personalize oral anticoagulation therapy in the wider population as it moves, inevitably, toward increasing heterogeneity through admixed genomes.

Inclusion criteria

• Caribbean Hispanic origin (e.g., Puerto Ricans, Dominicans, Cubans), whose parents are Caribbean Hispanics as well
• Age ≥ 21 years and ≤90 years.
• Willingness and ability to sign informed consent.
• Able to be followed up over 3 months.
• Expected duration of warfarin therapy of at least 3 months.
• Anticoagulation management for the patient will be performed in-hospital and/or as an outpatient by clinicians (i.e., participating Physicians, PharmD) that will adhere to the study dosing algorithms and dose-titration plans.

Exclusion criteria

• Non-Hispanic patients (race/ethnicity is self-reported by the patients)
• Age <21 years and >90 years.
• Currently taking warfarin or any other new oral anticoagulant (e.g., Xarelto, Pradaxa, Eliquis, and Savaysa/Lixiana).
• Prior warfarin therapy with known required stable dose.
• Clinician opinion that warfarin dosing needs to be adjusted for reasons not accounted for by dosing algorithm (i.e., other than age, gender, body size, co-meds, comorbidities, diet, genetics, ancestry, INRs and target INR).
• Abnormal baseline INR (off warfarin), e.g., due to liver disease, antiphospholipid antibody
• Contraindication to warfarin treatment for at least 3 months.
• Life expectancy of less than 1 year.
• Pregnant women or childbearing women not using medically approved method of birth control.
• Inability to follow-up on a regular basis with anticoagulation practitioners participating in trial.
• Any factors likely to limit adherence to warfarin, (e.g., dementia, alcohol or substance abuse, plans to move in the next 3 months, history of unreliability in medication taking or appointment keeping, significant concerns about participation in the study from spouse, significant other, or family members, lack of support from primary health care provider).
• Sickle cell, HIV-positive/ AIDS patients
• Cognitive or other causes of inability to provide informed consent or follow study procedures.
• Participating in another trial that prohibits participation in the current trial or planned enrollment in such a trial within the first 3 months of warfarin therapy.
• Anemia: a reduction in Hg ≥2g/dl within 48 hours before randomization and requiring blood transfusions.
• Creatinine Clearance (CrCL) ≤ 15 mL/min.
• Genotype (CYP2C9 or VKORC1) known to participant from prior testing.