ICAAC: Tygacil Beats Resistant Acinetobacter

SAN FRANCISCO, Sept. 28 -- The antibiotic Tygacil (tigecycline) is highly effective against multidrug resistant strains of acinetobacter, which are an increasing problem in intensive care units, researchers reported here.

Usually, the bacterium is sensitive to a range of antibiotics, according to Ronald Jones, M.D., of JMI Laboratories in North Liberty, Ind., but when resistance occurs, Acinetobacter can cause serious illness, including pneumonia, bacteremia and deep wound infections."

And in the past few years, he said at the Interscience Conference on Antimicrobial Agents and Chemotherapy here, "the number of (acinetobacter) organisms as a cause of bacteremia and serious pneumonia, particularly in ICU patients, has dramatically increased."

In a lab analysis financed by Wyeth Pharmaceuticals, the makers of the drug, Dr. Jones and colleagues tested Tygacil against 327 strains of acinetobacter collected from patients in North America from 2003 through 2005.

The drug, Dr. Jones said, was highly active against all strains, including those resistant to 11 of the major antibiotics. For those strains, he said, 90.2% of isolates were susceptible at a minimal inhibitory concentration of two micrograms per milliliter.

The catch is, he said, that Tygacil is only approved for complicated skin and intra-abdominal infections. So physicians are using it off-label.

"It's being used in medical centers for salvage therapy for patients who are resistant," Dr. Jones said, simply because resistant acinetobacter is a growing problem with no clear answer.

"We've used it on a number of occasions against acinetobacter," said Robert Rapp, PharmD, of the University of Kentucky's Chandler Medical Center in Lexington, adding that the clinical utility of the drug is limited by lack of data on the correct dosing levels to treat acinetobacter infection.

But for rare indications such as acinetobacter infection, Dr. Rapp said, "it would be very difficult to get enough data for FDA approval," which would at the same time give doctors clear guidance on what doses are appropriate.

"Almost all tigecycline use is off-label," Dr. Rapp said.

He added that Tygacil, approved in June 2005, is the "only new antibiotic for Gram-negative bacteria since 1988."

In another presentation, researchers from International Health Management Associates, supported by a grant from Wyeth, showed that Tygacil is active against infection-causing bacteria isolated from patients of all ages.

More than 38,000 clinically significant isolates were tested against the drug, according to Sam Bouchillon, M.D., and colleagues, and while the activity of the drug varied slightly within age groups and according to the organism being tested, the variations were consistently within FDA ranges for susceptibility

Indeed, the researchers said, more than 90% of all isolates tested were susceptible to the drug, regardless of age.