Antibiotic penetration in abdominal infection: a case of tobramycin failure responsive to moxalactam

A 50-year-old male developed an Enterobacter cloacae abdominal infection as the result of gangrene of a gastric remnant after gastrectomy. Aggressive antibiotic treatment with tobramycin and clindamycin was instituted, but despite documented in vitro bacterial sensitivity and high serum tobramycin levels, the patient's clinical condition worsened. Enterobacter cloacae continued to grow in the abdominal drainage cultures. As a last resort, moxalactam therapy was started. Within 36 hours, dramatic clinical improvement was seen and Enterobacter disappeared from the abdominal fluid cultures. Antibiotic assays showed that abdominal fluid contained approximately 50 percent of the simultaneous serum moxalactam concentration, while tobramycin was present in abdominal fluid at less than 15 percent of the serum concentration. In spite of bacterial sensitivity to both drugs, it is likely that moxalactam produced better results than did tobramycin, because of better tissue penetration characteristics.