Experts disagree on approaches to rifapentine
Time to try out the new drug, or better to wait?
With a good report card from the TB Trials Consortium, rifapentine is the new anti-TB drug on the block. As more data on the drug come in over the next few years, researchers will be able to fine-tune dosages, but for now, some TB experts say it’s time to take the new drug for a walk, while others say it’s wiser to wait.
"It’s a good drug, but studies so far don’t represent its optimal use," says Michael Iseman, MD, chief of the clinical mycobacteriology service of the Infectious Disease Section at National Jewish Hospital in Denver. "Rather than risk treatment failures and drug resistance, I think it should be held in abeyance for the general community. We should reserve it only for the next generation of studies now on the drawing board."
What he especially dreads are physicians without TB expertise tinkering with the drug. "I don’t mean to be arrogant and ivory-tower, but what I worry about is physicians in the general community using this drug in an uncontrolled way," he says. "Then we’ll start having problems, and the drug will get a bad name. It’ll become that new drug that didn’t deliver.’"
Too, misusing the drug could generate resistance and take away the only new weapon to be added to the TB pharmacy in decades. "I’m not thinking so much here about the loss to people here in the United State, but overseas," he explains. "Our TB problem is small potatoes compared to the rest of the world."
On the other hand . . .
Although he doesn’t disagree, one of Iseman’s colleagues in Denver, Randall Reves, MD, MSc, medical director of the town’s TB control program, says he thinks a well-run program should be able to use the new drug on select patients without problems. Reves should know, because that’s exactly what he’s been doing, having used rifapentine to treat "a handful" of regular clinic patients in the continuation phase of therapy.
The once-weekly drug comes especially handy when the patients have steady jobs or long travel times, making it tough to show up twice weekly for pills, Reves says. When he used the drug as part of the TBTC study, Reves says such patients jumped at the chance for the once-weekly treatment. "Even though they knew it was experimental at that point, the issue of having to deal with treatment just once a week is clearly very appealing to patients."
As the TBTC study shows, not everyone is a good candidate for the drug, Reves notes. Those who do meet the requirements suggested by experts — namely, no cavitation and the ability to take their meds reliably — account for at least half the people Reves sees. The fact that continuation-phase treatment is pared to once a week acts as its own compliance-booster, he adds. "I suspect as we look back at these patients and compare them [to those on standard therapy], we’ll see some rates [of completion] that are pretty good."
What piques Reves’ curiosity is that the rifapentine study found patients who fail to convert their sputum by eight weeks are likely to have problems either way, whether on either rifapentine or on standard therapy. "It raises the question of whether we should be using a more intensive regimen on that group," he says.
Indeed, optimal treatment for that small subgroup of patients is now under consideration, with new guidelines due out in a year or so, says Rick O’Brien, MD, chief of research and evaluation at the Division of TB Elimination at the Centers for Disease Control and Prevention in Atlanta.
In groups of patients who start treatment with a substantial load of microorganisms, between 20% and 30% still may be at least smear-positive (if not culture-positive) after two months of treatment, says O’Brien. By three months’ time, upwards of 95% of patients will have converted their culture status to negative. For those who don’t, the study committee might well recommend changing course by reverting to daily therapy, by extending treatment, or by some other means.
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