Body: Tacrolimus is an immunosuppressant commonly prescribed for transplant recipients. It has a narrow therapeutic window, with acute rejection resulting from insufficient dosing, and increased risk of kidney injury and drug toxicity associated with increased blood concentrations. Tacrolimus is metabolized by the CYP3A5 enzyme, where reductions in CYP3A5 activity cause decreased metabolism leading to more rapid increases in blood concentration level for a given dose of the drug. Identifying an individual’s CYP3A5 expression level is therefore essential for proper tacrolimus dosing. Three CYP3A5 alleles (*3, *6 and *7) are associated with full or partial loss of protein activity depending on zygosity. Both the Dutch Pharmacogenetic Working Group (DPWG) as well as the Clinical Pharmacogenetics Implementation Consortium (CPIC) agree on recommendations for tacrolimus dosing based on CYP3A5 genotyping for the *3, *6 and *7 alleles.
We have developed a test for CYP3A5 *3, *6 and *7 genotyping. The test uses a 6-plex qPCR assay format with a high level of reliability. We completed analytical performance testing by assessing accuracy, sensitivity, precision and robustness of TacroType using multiple sources of human DNA. Accuracy was confirmed for each possible genotype at all three alleles using well-characterized reference samples. TacroType exhibited accurate and robust performance within a broad range of DNA input. Precision studies indicated consistent assay results across operators, instruments and lots of reagent. Accurate and consistent assay performance was demonstrated using EDTA and ACD blood and buccal swabs prepared by a variety of DNA extraction method.
Conclusion: We have developed a robust and rapid test to detect CYP3A5 *3, *6 and *7 genotyping. TacroType is accurate, sensitive, precise and is suitable for use with blood and buccal swab samples.
