Susceptibility patterns of bacteria following therapy with piperacillin

We reviewed case reports of all patients treated with piperacillin submitted to Cyanamid Medical Research between January 1978 and July 1981 in order to determine how often and under what circumstances resistance to piperacillin develops during therapy. Overall, 19© 1482 (1.3%) bacteria became resistant. If only evaluable courses of therapy are counted, 17©1076 (1.6%) bacteria became resistant resulting in persistence of bacteria in 15©1076 (1.4%) instances and clinical failure or relapse in 8©1075 (0.74%). Emergence of resistance was associated with aerobic Gram-negative bacillary infections, especially Pseudomonas infections, prolonged therapy and possibly underdosing, less susceptible initial isolates, and cystic fibrosis. We concluded that emergence of resistance was uncommon and relatively unimportant for the types of patients included in this study.