Vol.64 No.3 May 2016

Efficacy of vancomycin for methicillin-resistant Staphylococcus aureus strains with minimum inhibitory concentration of 1 and 2 μg/mL in the Prompt method using a MicroScan^® Pos Combo 3.1J panel

Naoya Tagui¹⁾, Yoshiko Suzuki²⁾, Masayoshi Kondo¹⁾, Makihiko Nagano¹⁾, Masato Yoshida¹⁾, Kazutoshi Sugaya¹⁾, Hiroshi Maruyama³⁾, Hidemasa Nakaminami⁴⁾, Norihisa Noguchi⁴⁾ and Kazuya Murata¹⁾

¹⁾Department of Pharmacy, Nippon Medical School Tama Nagayama Hospital, 1-7-1 Nagayama, Tama, Tokyo, Japan
²⁾Department of Central Clinical Laboratory, Nippon Medical School Tama Nagayama Hospital
³⁾Department of Surgery, Nippon Medical School Tama Nagayama Hospital
⁴⁾Department of Microbiology, School of Pharmacy, Tokyo University of Pharmacy and Life Sciences

Abstract

In recent years, the index, an AUC_0-24/MIC, of ≥ 400 mg・h/L has been considered as a predictor for the clinical and bacteriological efficacy of vancomycin (VCM) treatment of methicillin-resistant Staphylococcus aureus (MRSA) infections. In addition, an MIC of ≥2 μg/mL is associated with a higher rate of failed VCM treatment. However, the AUC_0-24/MIC values vary depending on the method used for their measurement. It has been reported that the Prompt method revealed higher VCM MIC values than the reference turbidity method when the MicroScan^® Pos Combo 3.1J panels manufactured before April 2015 were used.
In this study, we compared the efficacy of VCM treatment in 49 patients with various MRSA infections admitted to our hospital between April 2011 and December 2014. Patients were divided into two groups according to the MIC of either 1 or 2 μg/mL measured using MicroScan^® Pos Combo 3.1J panels (Prompt method). The relevance of MICs measured by this method to the therapeutic efficacy of VCM was examined.
Comparison of the efficacy rates between the two MIC groups (1 vs. 2 μg/mL) showed no significant difference in the therapeutic efficacy of VCM among all patients with MRSA infections (40.7% vs. 63.6%, p = 0.114), patients with MRSA pneumonia (47.1% vs. 70%, p = 0.347), and patients with MRSA sepsis (50% vs. 50%, p = 1.000). Consequently, no correlation was found between MIC measured by the Prompt method and therapeutic efficacy of VCM in the two groups. Thus, these measurements were considered difficult for direct use when predicting the therapeutic efficacy of VCM. However, the results also suggest that a therapeutic efficacy comparable with that for MRSA strains with an MIC of 1 μg/mL can be obtained for strains with MIC of 2 μg/mL by achieving an AUC_0-24/MIC of ≥400 mg・hr/L. This represents another basis to suggest that appropriate therapeutic agents should be selected after completely understanding the characteristics of the test method used, rather than solely relying on the measured MIC values.

Key word

MRSA, vancomycin, area under the curve, MIC, efficacy

Received

September 3, 2015

Accepted

January 19, 2016

Jpn. J. Chemother. 64 (3): 530-538, 2016