Treatment of experimental chronic osteomyelitis caused by Morganella morganii with mezlocillin and cloxacillin.

Mezlocillin was used alone and in combination with cloxacillin in the treatment of chronic experimental osteomyelitis due to Morganella morganii. This combination showed in vitro synergy as measured by the checkerboard technique. A marked inoculum affect was demonstrated in vitro with mezlocillin and the infecting strain of M. morganii. In therapeutic trials, mezlocillin administered for 28 days was totally ineffective. The combination of mezlocillin and cloxacillin (at 800 and 400 mg/kg, respectively, 4 times a day) given for 28 days was significantly better than either no therapy or therapy with mezlocillin alone. However, even after 4 weeks of combined therapy with mezlocillin and cloxacillin M. morganii was recovered from the bones of 55% of the treated rabbits.