Combined imipenem/cilastatin and tobramycin therapy of multiresistant Pseudomonas aeruginosa in cystic fibrosis.

Ten patients with cystic fibrosis (CF) and chronic broncho-pulmonary Pseudomonas aeruginosa infection were given imipenem/cilastatin (100 mg/kg/day) in combination with tobramycin (15 mg/kg/day). Forced vital capacity and forced expiratory volume in the first second improved significantly in nine out of ten patients, and most of the patients improved clinically. P. aeruginosa was not eradicated in any patient and resistance against imipenem developed in all patients during treatment. A concomitant increase in MIC of piperacillin and ceftazidime occurred during treatment. In-vitro bactericidal synergy of imipenem and tobramycin was noted in 57% of pretreatment isolates. Seven patients complained of adverse reactions, mainly gastrointestinal, and treatment of three patients was discontinued after 5, 8, and 12 days of therapy, because of rash or nausea and vomiting. The side effects were considered to be due to imipenem/cilastatin. Because of the rapid development of imipenem resistance despite combination therapy, the high proportion of side effects, and the risk of induction of beta-lactam resistance, imipenem/cilastatin cannot be recommended for routine treatment of CF-patients with P. aeruginosa infection.