Clinical trial of piperacillin with acquisition of resistance by Pseudomonas and clinical relapse.

A total of 20 serious infections were treated with piperacillin. These infections included bacteremias (5), pneumonias (5), urinary tract infections (5), soft tissue infections (3), septic arthritis (1), and osteomyelitis (1). The most common bacterial pathogen was Pseudomonas aeruginosa, accounting for eight infections. The clinical and bacteriological response rates were 75 and 70%, respectively. Four of the five patients who failed to respond to piperacillin therapy were infected with Pseudomonas. In two patients with Pseudomonas infections clinical relapse was accompanied by the development of piperacillin-resistant P. aeruginosa. The findings suggest that the use of piperacillin as a single agent for the treatment of serious gram-negative infections may be ill-advised, especially if P. aeruginosa is the offending pathogen.