January 4, 2010
Researchers have reported the case of a TB strain in a patient in China that actually thrives in the presence of the first-line TB drug rifampin. The 35-year-old patient failed to respond to the World Health Organization's optional thrice-weekly treatment, which included rifampin and other first-line TB drugs. The condition worsened on a second-line drug regimen that also contained rifampin.
On further examination, researchers found the patient's multidrug-resistant TB (MDR-TB) strain was dependent and/or enhanced by rifampin. The patient recovered once the drug was removed from the treatment regimen.
"Rifampin-dependent tuberculosis is an unrecognized and potentially serious treatment issue," said lead study author Ying Zhang, MD, PhD, of the Bloomberg School of Public Health. "Rifampin resistance is ominous. Our study highlights the potential dangers of continued treatment of MDR TB with rifamycins that occur frequently due to delayed or absent drug susceptibility testing in the field. Further studies are urgently needed to determine how common such rifampin-dependent MDR TB is in field conditions and if it contributes to the worsening of the disease in MDR patients and treatment failures."
The TB strain is normally difficult to detect, since it grows poorly in the absence of rifampin, Zhang noted. Timely detection would involve adding the drug to culture media, and switching to rifampin-free treatment regimens if enhancement or dependency were detected. However, there are time and resource barriers to such testing in the field, especially in poor regions, he said.
The full study, "An Interesting Case of Rifampicin-Dependent/-Enhanced Multidrug-Resistant Tuberculosis," was published in the International Journal of Tuberculosis and Lung Disease (2010;14(1):40-44(5)).