Assess genetic risk of abnormal drug metabolism for drugs metabolized by CYP3A5. May aid in drug selection and dose planning for drugs metabolized by CYP3A5.
- Patient Preparation
- Lavender (EDTA), pink (K2EDTA), or yellow (ACD Solution A or B).
- Specimen Preparation
- Transport 3 mL whole blood. (Min: 1 mL)
- Storage/Transport Temperature
- Unacceptable Conditions
- Plasma or serum. Heparinized specimens.
- Ambient: 72 hours; Refrigerated: 2 weeks; Frozen: 1 month
Characteristics: The cytochrome P450 (CYP) 3A subfamily of enzymes is involved in metabolism of many drugs such as immunosuppressants, antibiotics, antivirals, benzodiazepines, and steroids. Nonfunctional variants of CYP3A5 are common in some populations, preventing expression and function of the CYP3A5 enzyme, which will influence pharmacokinetics of CYP3A5 substrates, and may predict non-standard dose requirements.
Inheritance: Autosomal co-dominant.
Cause: CYP3A5 gene variants result in enzyme deficiency.
Variants Tested:CYP3A5 non-functional alleles: *3 (rs776746, c.6986A>G), *6 (rs10264272, c.14690G>A).
Negative: No variants detected is predictive of *1 functional alleles and normal CYP3A5 enzyme activity. (Variants are numbered according to NG_007938.1 transcript)
CYP3A5*3: African 29.8 percent, Asian 74.2 percent, Caucasian 92.1 percent, Latin American 76.5 percent, Middle Eastern 88.1 percent
CYP3A5*6: African 17.2 percent, Asian 0.1 percent, Caucasian 0.1 percent, Latin American 3.7 percent, Middle Eastern 1.9 percent
CYP3A5*7: African 7.7 percent, Asian 0 percent, Caucasian 0 percent, Latin American 2.5 percent, Middle Eastern 0.2 percent
Clinical Sensitivity: Drug-dependent.
Methodology: Polymerase chain reaction(PCR) and fluorescence monitoring.
Analytical Sensitivity and Specificity: Greater than 99 percent.
Limitations: Only the targeted CYP3A5 variants will be detected by this panel. Diagnostic errors can occur due to rare sequence variations. Many CYP3A substrates are also metabolized by CYP3A4, for which clinically relevant genetic variation is not recognized to be common. Risk of therapeutic failure or adverse reactions with CYP3A5 substrates may be affected by genetic and non-genetic factors that are not detected by this test. This result does not replace the need for therapeutic drug or clinical monitoring.
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