Is treatment of acute exacerbations of chronic bronchitis with intramuscular mezlocillin justifiable?

A group of patients admitted to hospital with acute purulent exacerbations of chronic bronchitis was treated with two daily injections of 1 or 2 g mezlocillin intramuscularly for ten days, 19 patients receiving 1 g and 17 the 2 g doses. Serum and sputum mezlocillin concentrations were measured microbiologically on the first treatment day. The peak serum levels averaged 23 mg/l after 1 g and 34 mg/l after 2 g, and the corresponding average sputum peak concentrations were 0.78 and 1.26 mg/l respectively. Fourteen of the 36 patients had infections associated with beta-lactamase-producing bacteria and nine of the positive cultures on the last treatment day also showed beta-lactamase producers to be present. Most of the MICs for the sensitive bacteria were of the order of 2-4 mg/l, but the MICs for the Pseudomonas aeruginosa strains were greater than 16 mg/l. Mezlocillin was relatively inactive against many of the common respiratory pathogens--even when these were not beta-lactamase producers--by virtue of poor penetration.