Imagine there is a relatively common allele in Southeast Asian populations that puts carriers at a thousand-fold risk of developing a debilitating disease as a result of taking a commonly prescribed generic drug. Imagine, too, that an available genetic test can determine whether a patient is positive for that allele so that clinicians can prescribe an alternative — albeit more expensive — treatment. Now envision that this test — when performed on each patient prescribed the generic — could save millions of dollars in health care spending every year.
According to Luke Chen, the chief executive officer of the Taipei, Taiwan-based Pharmigene, all of the above are true in the case of carbemazepine-induced Stevens-Johnson syndrome, a condition that can lead to toxic epidermal necrosis. "Using HLAB*1502 genotyping as a screening tool, [clinicians] can effectively reduce the incidences of Stevens-Johnson and TEN" in patients prescribed carbemazepine, Chen said at the American Association for Clinical Chemistry meeting in July.
Carbemazepine is approved to treat epilepsy and biopolar disorder, though up to 60 percent of scripts for the drug written in Southeast Asia are for off-label use, Chen said.
The US Food and Drug Administration, aware of data from HLAB*1502 studies published in Nature in 2004, called for a relabeling of the drug in 2007 to recommend that patients be genotyped before beginning treatment.
Approximately 50,000 patients in Taiwan are prescribed carbemazepine for the first time each year. Of those, about 115 are HLAB*1502-positive, and an estimated six of those people will experience severe, and costly, complications — such as handicap or death — as a result of Stevens-Johnson-TEN. That allele is observed almost exclusively in Southern Han Chinese and Southeast Asian populations, at frequencies of eight and 20 percent, respectively.
Chen and his collaborators at Academia Sinica have shown in a prospective clinical trial of nearly 5,000 patients that HLAB*1502 genotyping can effectively reduce the occurrence of Stevens-Johnson-TEN. They also set out to determine whether "it [makes] sense when you attach a very inexpensive drug with a very expensive genetic test," Chen said.
Taiwanese health agencies could save on the order of $35 million over five years were they to cover the cost of genotyping — about $100 — for all patients and prescribe carbemazepine only to those deemed HLAB*1502-negative. HLAB*1502-positive patients could take an alternative drug.
"As we talk about personalized medicine, I think this is one of the cases that is the most clear-cut of how it … can be effectively used," Chen said.