Assessment of Differences in Antimicrobial Effect Determined with Two In Vitro Pharmacodynamic Models: Impact of Surface Area to Volume Ratio

Roger L. White, Pharm.D., Charles R. Bonapace, Pharm.D., Lawrence V. Friedrich, Pharm.D., Michael J. Rybak, Pharm.D., Diane M. Cappelletty, Pharm.D., Renee-Claude Mercier, Pharm.D., Heather H. Houlihan, Pharm.D., Jeffrey R. Aeschlimann, Pharm.D., John A. Bosso, Pharm.D.

Pharmacotherapy. 2003;23(5) 

In This Article


The modal MIC for P. aeruginosa ATCC 27853 using ceftazidime E test strips was 5 µg/ml. Figure 3 shows concentration-time profiles for central and peripheral compartments. Mean central compartment ceftazidime concentrations were 23.5 and 20.9 µg/ml for models A and B, respectively. Ceftazidime penetration into the peripheral compartment occurred more rapidly in model A than in model B (Figure 4). The percentage of penetration from 0-4 hours was 53% greater for model A ( Table 1 ); however, the value over the entire study period was similar for both models (4% difference). No appreciable change in colony counts was observed before 2 hours in either model (lag effect; Figure 5); however, thereafter, counts were higher in the growth control curve and killing was more extensive in model A than in model B. No bacterial regrowth was observed in either model. The percent effect was greater in model A than in model B from both 0-4 hours (64% greater) and 0-24 hours (38% greater).

Percent of ceftazidime penetration into peripheral compartments from 0-4 hours. Model A (), model B ().

Surviving colony counts versus time. Model A growth control curve (), model A kill curve (), model B growth control curve (), model B kill curve (). CFU = colony-forming units.


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