Studies on the effect of mecillinam upon Micrococcaceae and faecal streptococci under conditions simulating urinary tract infection

Pivmecillinam is an ester of a new penicillin analogue which is hydrolysed after absorption by non-specific esterases to release mecillinam. Micrococcaceae appear to be very resistant to mecillinam by the conventional antibiotic sensitivity test with paper disks containing 10 μg of antibiotic. However, the MIC's of mecillinam for 35 urinary isolates of Micrococcaceae was found to be much lower than urinary concentrations, and urine from volunteers receiving therapeutic doses of pivmecillinam was cidal for almost all isolates. Experiments with urine containing added mecillinam suggest that uncomplicated urinary tract infections by Micrococcaceae may be expected to respond to treatment with pivmecillinam. A disk containing 50 μg of mecillinam may more accurately predict the outcome of treatment than the 10 μg disk previously used. Comparable studies suggest that standard doses of pivmecillinam are unlikely to be effective in the majority of cases of urinary infection by faecal streptococci.