TB Continued

[Editor’s note: In his Top Papers of the Month column, “Biological Agents and the Risk of Mycobacterial Disease: A Primary Care Concern” (CONSULTANT, July 2011, page 461), Dr Gregory Rutecki wrote, “[T]he results of skin tests (either Mantoux or purified protein derivative) can be false-negative in 20% to 25% of patients with active TB who are not simultaneously infected with HIV. How does this fact change the approach to screening? Higher-risk patients, that is, persons from endemic areas or those exposed as a result of travel, may be better served by the QuantiFERON-TB Gold test, which is more sensitive in persons with RA from TB-endemic areas. . . . Treatment of latent TB in these same patients requires isoniazid (for 6 to 9 months), but the regimen should also include a second agent, rifampin, for 4 months.”¹

A reader recently responded to these remarks.]

These recommendations misquote Dr Iseman’s article. Latent tuberculosis is treated with isoniazid for 6 to 9 months or rifampin for 4 months, not both. There is a promising study of short-course combination (isoniazid plus rifapentine) therapy that is not yet published. The current standard is monotherapy. Compared to isoniazid, rifampin has advantages (shorter duration,
less hepatotoxicity, lower frequency of resistance) and disadvantages (more drug interactions, other toxicities, higher cost and, most important, the risk of inducing rifampin resistance if active disease develops during treatment). Combination therapy is generally reserved for active tuberculosis.

With respect to Quantiferon testing, to quote Dr Iseman, “the value of IGRAs over the TST is not fully delineated.”¹ Most of the studies have looked at its performance in active tuberculosis, not its ability to predict who will develop reactivation disease. The optimal testing strategy remains an unresolved issue.

Jonathan Blum, MD


Thank you for your careful reading. The correction suggested is absolutely on target, that is, in the context of latent TB, therapy is monotherapy, either/or, isoniazid or rifampin, not both.

I also agree that the role of IGRAs is not fully delineated; that is why I used “may.”

Gregory W. Rutecki, MD
Professor of Medicine
University of South Alabama College of Medicine
Mobile

Reference
1. Iseman MD. Mycobacterial infections in the era of modern biologic agents. Am J Med Sci. 2011;341:278-280.