GlaxoSmithKline says retapamulin lab studies show potency against skin-infection pathogens

By E. Janene Geiss

Philadelphia, Dec. 19 - Glaxo SmithKline said Monday that studies of its investigational antibacterial retapamulin showed an excellent microbiology profile and a high degree of in vitro potency in laboratory studies against key pathogens commonly associated with skin and soft tissue infections, consistently showing potent activity when compared to other commonly-prescribed topical and oral antimicrobial agents.

Retapamulin also showed a low propensity for development of resistance in target pathogens, according to a company news release.

Retapamulin belongs to a new class of antibiotics called pleuromutilins and is being developed for the topical treatment of uncomplicated skin and skin-structure infections due to susceptible strains of staphylococcus aureus or streptococcus pyogenes, officials said.

In one laboratory study, researchers from International Health Management Associates and GlaxoSmithKline determined the minimum inhibitory concentration of retapamulin against more than 3,700 clinical isolates of staphylococci, beta-hemolytic and viridans streptococci, collected from patients at 17 sites across North America.

The results demonstrated that retapamulin has excellent in vitro antibacterial activity against the organisms tested, officials said.

The concentration of antibacterial required to inhibit the growth of 90% of bacteria tested was lowest for retapamulin when compared to thirteen other agents tested, including mupirocin, amoxicillin/clavulanic acid, erythromycin and fusidic acid.

Another laboratory study, led by researchers from Hershey Medical Center, looked at the potential for S. aureus to develop resistance to retapamulin and seven other commonly-used antibacterials, including mupirocin, cephalexin, vancomycin and fusidic acid.

Researchers tested the ability of antibacterials to select the drug resistant clones among 12 S. aureus strains.

The results showed that retapamulin demonstrated excellent activity against the 12 S. aureus isolates tested and had a low frequency of spontaneous mutations affecting the activity of the compound against S. aureus.

The development of S. aureus resistance following daily passage in the presence of sub-inhibitory antibiotic concentrations occurred faster for mupirocin and fusidic acid than for retapamulin, officials said.

Overall, the results demonstrate that retapamulin has a low propensity to generate resistance in S. aureus, officials said.

The data, along with data from further in vitro work, also suggest that retapamulin could offer a new treatment option against S. aureus and S pyogenes in skin and skin-structure infections.

"These studies showed that retapamulin not only demonstrated promising in vitro activity against these specific types of bacteria, it also may have a low propensity to generate drug resistance," said Clarence Young, vice-

president of Infectious Diseases Medicines Development Center, GlaxoSmithKline, in the release.

The studies were presented Monday at the Interscience Conference of Antimicrobial Agents and Chemotherapy in Washington, D.C.

GlaxoSmithKline is a pharmaceutical company with U.S. operations in Philadelphia and Research Triangle Park, N.C.

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