Question 7

Is the strategy of administering doses above the MPC also beneficial when treating other Gram-positive pathogens and Gram-negative pathogens such as Pseudomonas aeruginosa and Escherichia coli?

MPC determinations have been used as part of the rationale for using higher drug dosage regimens when treating P. aeruginosa . They have demonstrated that the concentration needs to be increased slightly to avoid the appearance of resistance. It is also useful to know the Escherichia coli (E. coli ) MPC value when treating urinary tract infention (UTI). A recent Spanish study has evaluated MPC in E. coli as a method of evaluating the capacity of levofloxacin and ciprofloxacin for restricting the development of resistant mutants. 99 isolates with differing fluoroquinolone susceptibilities were divided into extended spectrum beta-lactamase (ESBL)-producing and non- ESBL producing isolates. Results demonstrated that isolates with this resistance mechanism (ESBL-producing) had a greater probability of developing clinical resistance than non-ESBL producing isolates, even in strains shown to be susceptible during normal testing, making it useful to know this value (8).