The FDA cleared a new blood test to aid physicians in pinpointing safe dosages of Pfizer's chemotherapy drug Camptosar.
The blood test, known as the Invader UGT1A1 Molecular Assay, is approved for identifying patients who may run an increased risk of adverse reaction to Camptosar (irinotecan) by detecting specific variations of the UGT1A1 gene.
Not enough data is available to link the test to other chemotherapeutic agents at this time, said Alberto Gutierez, FDA toxicology team leader in the agency's Office of In Vitro Diagnostics.
"It is pretty limited at this point to irinotecan," he told MM&M.
The UGT1A1 gene affects how irinotecan is metabolized. The mutation the test is designed to look for can slow the body's ability to break down the drug, leading to toxicity in patients.
Third Wave Technologies, maker of the assay, says such information can be useful in helping doctors lower the risk of harmful side effects by decreasing the dose in patients with the mutation. Camptosar's label was recently updated to reflect dosing recommendations based on a patient's genetic predisposition to this risk.
"While the pharmacogenetic market is just beginning to emerge, we believe it will become increasingly valuable," said John J. Puisis, president and CEO of Third Wave, in a statement.
The FDA, in a statement of its own about the approval, said 66 patients receiving irinotecan therapy were part of a study submitted as part of the application for the test. Subjects with one type of UGT1A1 variation showed a five times greater risk of experiencing a dangerous buildup of irinotecan in the blood.
The Invader assay itself was not used in the testing, according to Gutierez; another assay was. But bridging studies correlated the test to work just as well as the one used, he explained.
Invader is the latest pharmacogenetic diagnostic designed to tailor dosages of drugs. The field also includes Roche's AmpliChip, which is used for dosing some chemotherapy agents, as well as antidepressants, antipsychotics and beta-blockers. Another blood test, TRUGENE HIV-1 Genotyping Kit is designed to detect variations in the genome of the human immunodeficiency virus that make it resistant to some anti-retroviral drugs.