CHICAGO--Coaxed by a Boston-based advocacy group, two giant drug companies have released proprietary data on antibiotic resistance. The new figures, presented here 17 December at the meeting of the Interscience Conference on Antimicrobial Agents and Chemotherapy, show that deadly pneumonia-causing microbes have begun to evade ciprofloxacin (Cipro) and other drugs belonging to a class of antibiotics called fluoroquinolones.
For the last decade, physicians have relied on fluoroquinolones to wipe out various bacteria, including bugs that cause pneumonia, skin infections, gonorrhea, and even anthrax. The microbes can evolve resistance to fluoroquinolones in the laboratory. To determine whether this is happening in hospitals, the Alliance for the Prudent Use of Antibiotics (APUA) in Boston began pressing major drug companies to reveal antibiotic resistance data. Recently, Bristol-Myers Squibb and GlaxoSmithKline agreed to share their information about tests on clinical isolates of Hemophilus influenzae, the second leading cause of bacterial pneumonia death in children in the developing world.
Drug company researchers have for years been collecting thousands of H. influenzae isolates from patients in hospitals and clinics across North America and Europe. In the lab, they grow the samples in cultures that contain various levels of either of two fluoroquinolones, ciprofloxacin and ofloxacin. Fully resistant bugs can survive antibiotic concentrations 16 times as high as would kill a susceptible bug. But because bacteria often develop resistance gradually by undergoing a series of mutations, the drug company counted those that survived levels of drug just 2 times what's normally deadly. This strategy allows a glimpse into resistance in the making, says microbiologist Stuart Levy of Tufts University School of Medicine in Boston, president of APUA.
The two companies revealed that fewer than 0.1% of microbe samples collected before 1997 had gained some resistance to the drugs. But since 2000, the incidence of partial resistance has increased slightly to about 0.15%. Other drug firms are thought to be also gathering this type of data, though it remains proprietary.
Pharmacologist Michael Dudley of Microcide Pharmaceuticals in Mountainview, California, calls the study well done, although he cautions that it's still hard to tell if resistance is on the rise because the incidence is so low.