Blood Test Helps Docs Personalize Drug Treatments

Today, FDA cleared for marketing a new blood test that will help doctors make personalized drug treatment decisions for some patients. The Invader UGT1A1 Molecular Assay detects variations in a gene that affects how certain drugs are broken down and cleared by the body. Doctors can use this information to help determine the right drug dosage for individual patients, and minimize harmful drug reactions.

“This test represents the power of DNA-based testing to provide individualized medical care,” said Daniel Schultz, MD, Director of FDA’s Center for Devices and Radiological Health. “These technologies can significantly improve patient management and reduce the risk of ineffective or even harmful drug therapy by telling doctors how to individualize drug dosing.”

The Invader assay joins a growing list of genetic tests used by physicians to personalize treatment decisions, including the Roche AmpliChip, used to individualize dosage of antidepressants, antipsychotics, beta-blockers, and some chemotherapy drugs, and TRUGENE HIV-1 Genotyping Kit, used to detect variations in the genome of the human immunodeficiency virus that make the virus resistant to some anti-retroviral drugs.

The Invader assay detects variations in a gene called UGT1A1 that produces the enzyme UDP-glucuronosyltransferase. This enzyme is active in the metabolism of certain drugs, such as irinotecan, a drug used in colorectal cancer treatment. Variations in the UGT1A1 gene can influence a patient’s ability to break down irinotecan, which can lead to increased blood levels of the drug and a higher risk of side effects. For a patient with a particular UGT1A1 gene variation, a dose of irinotecan that is safe for another person might be too high for this patient, raising the risk of certain side effects. The Invader assay was studied in 66 patients who were receiving irinotecan therapy. The study showed that persons with one type of genetic variation have a five times greater risk of experiencing irinotecan toxicity.

“With the growing interest in individualizing drug therapy, FDA’s approval of this assay provides physicians and patients with important information on the proper dosage of drugs metabolized and cleared from the body by the UGT1A1 pathway,” said Lawrence Lesko, PhD, Director of FDA’s Office of Clinical Pharmacology and Biopharmaceutics in the Center for Drug Evaluation and Research. “Information on the UGT1A1 genotype can be an integral part of drug labels and will guide health professionals on how to dose medications such as irinotecan.”

The Invader assay is intended to aid a physician in making individualized patient treatment decisions. It is not a substitute for a physician’s judgment and clinical experience. Other important factors that may affect dosing should be considered, such as the patient’s liver function (measured in part by the level of bilirubin, a breakdown product of hemoglobin), age, kidney function, and co-administered drugs.

The Invader UGT1A1 Molecular Assay is manufactured by Third Wave Technologies, Inc., in Madison, Wisconsin.

From U.S. FDA

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