Impact of different pathophysiological conditions on antimicrobial activity of glycopeptides in vitro

Susceptibility testing is usually performed under standardized conditions for comparison of the activity of antimicrobial agents and the susceptibility of strains, but this does not reflect potential pathophysiological alterations at the infection site. While some impact factors have been studied already, there is a lack of knowledge about how different factors interact pharmacodynamically. We investigated the impact of albumin, pH and temperature in various combinations on the antimicrobial activity of glycopeptides.

Determination of minimal inhibitory concentrations (MICs) and time-kill curves were performed for telavancin, vancomycin and teicoplanin using 20 clinical isolates of Staphylococcus aureus and ATCC29213. The impact of the addition of 12% albumin, pH reduction to pH6, and temperature ranging from 32°C to 42°C was studied and compared to the standard setting in the reference medium Mueller Hinton broth (MHB).

At pH7 and 37°C the addition of albumin increased median MICs four-fold, eight-fold and two-fold for telavancin, teicoplanin and vancomycin, respectively. While changing temperature or pH alone had a moderate impact, the combination of albumin addition, pH decrease and temperature increase led to the maximum reduction of activity of 16-fold for teicoplanin compared to the standard setting. Temperature increase to 42°C increased the effect of albumin for teicoplanin and telavancin, resulting in ratios of 15.9 and 8. In contrast, reducing pH with concomitant albumin addition reduced the effect of albumin addition alone for telavancin, resulting in a ratio of 2 instead of 4.

Combining different impact factors showed a highly heterogeneous impact on the activity of glycopeptides. It might be misleading to take only protein binding into consideration in pharmacokinetic/pharmacodynamic (PK/PD) models.