New dipstick test for rifampin resistance

Research-use-only product may seek FDA approval

A strip-type rapid assay for rifampin resistance has begun clinical trials, says its manufacturer, Murex Diagnostics of Norcross, GA. The assay is called INNO-LiPA Rif-TB; if approved by the Food and Drug Administration, it should list for about $30 in the United States.

INNO-LiPA Rif-TB (the "LiPA" stands for "line probe assay") already is being marketed in several European countries, the United Kingdom, and South Africa. Sensitivity and specificity for the product have been rated at over 90%, says James McMenamin, FIMLS, director of marketing and sales for Murex.

"There's certainly been some interest in the test," says McMenamin, especially among those who work in high-prevalence parts of the United States. At present, INNO-LiPA is available in this country on a research-use-only basis, and positive results cannot be disclosed to patients before they are confirmed by conventional means.

To use the test, "you do your [polymerase chain reaction] and amplify your material in the normal way," says McMenamin. "The test itself is like a Western blot, or an immunoassay, on a strip."

It is designed to tell the test-reader two things: first, whether the specimen is Mycobacterium tuberculosis and second, whether the bug is rifampin-resistant. At present, the test is approved only for use on smear-positive specimens.

Despite the fact that positive results can't be given out, the test is still useful because it can alert clinicians "to a serious situation," he says. "We believe there's a good correlation between rifampin resistance and multidrug-resistant TB. And if someone has MDR-TB, you want to know that as soon as possible."

Though more conventional susceptibility testing will be needed before the right drug regimen can be prescribed, it's still handy to know what drugs won't work, he adds.

Plus, hospitals might decide to take extra precautions with someone who may have MDR-TB. Murex has a long-term licensing agreement with Innogenetics, the Zwijn drecth, Belgium, biotechnical firm that developed the test, McMenamin says.