Journal of Antimicrobial Chemotherapy (2002) 50, 281-284
© 2002 The British Society for Antimicrobial Chemotherapy
Calculation of composite recovery time: a new pharmacodynamic parameter
Medical Microbiology, Aberdeen Royal Infirmary, Foresterhill, Aberdeen AB25 2ZN, UK
Received 18 July 2001; returned 26 February 2002; revised 18 April 2002; accepted 2 May 2002
A new pharmacodynamic parameter, the composite recovery time (CRT), is described and used to calculate species-specific MIC breakpoints. Moxifloxacin data were used for illustration. This required determination of MICs, kill curves and post-antibiotic sub-MIC effect values. Thirteen test isolates included Staphylococcus aureus, Haemophilus influenzae and Streptococcus pneumoniae. The concentration at which the CRT equals the dosing interval is the minimum effective concentration, and is effectively the breakpoint. The breakpoints were calculated as 2 mg/L for the pneumococci and quinolone-susceptible H. influenzae isolate, 1 mg/L for staphylococci and 0.5 mg/L for Enterobacteriaceae. Calculated pharmacodynamic breakpoints were very similar to traditional published MIC breakpoints.
* Corresponding author. Tel: +44-1224-554957; Fax: +44-1224-550632; E-mail: f.m.mackenzie{at}abdn.ac.uk