Comparison of the risk of acquiring in vitro resistance to doripenem and tazobactam/piperacillin by CTX-M-15-producing Escherichia coli.

To compare the risk of acquiring in vitro resistance between doripenem and tazobactam/piperacillin by CTX-M-15-producing Escherichia coli, the in vitro frequency of resistance was determined. Four strains carrying multiple ß-lactamases such as blaOXA-1 or blaCTX-M-27 as well as blaCTX-M-15 and blaTEM-1 were used. No resistant colonies appeared on doripenem-containing plates, whereas resistant colonies were obtained from three of four test strains against tazobactam/piperacillin using agar plate containing 8- to 16-fold MIC of each drug. These three acquired tazobactam/piperacillin-resistant strains were not cross-resistant to doripenem, and they showed 1.9- to 3.1-fold higher piperacillin-hydrolysis activity compared to those of each parent strain. The change of each ß-lactamase mRNA expression measured by real-time PCR varied among three resistant strains. One of three tazobactam/piperacillin-resistant strains with less susceptibility to ceftazidime overexpressed both blaCTX-M-15 and blaTEM-1, and the other two strains showed higher mRNA expression of either blaTEM-1 or blaOXA-1. These results demonstrate that multiple ß-lactamases carried by CTX-M-15-producing E. coli contributed to the resistance to tazobactam/piperacillin. On the other hand, these resistant strains maintained susceptibility to doripenem. The risk of acquiring in vitro resistance to doripenem by CTX-M-15-producing E. coli seems to be lower than that to tazobactam/piperacillin.

The relationship between in vivo antiviral activity and pharmacokinetic parameters of peramivir in influenza virus infection model in mice.

The purpose of this study was to investigate the relationship between pharmacokinetic (PK) parameters of intravenous (IV) peramivir and in vivo antiviral activity pharmacodynamic (PD) outcomes in a mouse model of influenza virus infection. Peramivir was administrated to mice in three dosing schedules; once, twice and four times after infection of A/WS/33 (H1N1). The survival rate at day 14 after virus infection was employed as the antiviral activity outcome for analysis. The relationship between day 14 survival and PK parameters, including area under the concentration-time curve (AUC), maximum concentration (Cmax) and time that drug concentration exceeds IC95 (T(>IC95)), was estimated using a logistic regression model, and model fitness was evaluated by calculation of the Akaike information criterion (AIC) index. The AIC indices of AUC, Cmax and T(>IC95) were about 114, 151 and 124, respectively. The AIC of AUC and T(>IC95) were smaller than that of Cmax. Therefore, both AUC and T(>IC95) were the PK parameters that correlated best with the antiviral activity of peramivir IV against influenza virus infection in mice.

Effect of the chemical specificity of benzoic acid and its analogs on osmotic fragility in erythrocytes of Sprague-Dawley rats in vitro.

We examined the chemical specificity of benzoic (benzene-carboxylic) acid and its derivatives in increasing osmotic fragility (OF) in rat red blood cells (RBCs) in vitro. Benzoic acid increased the OF in the rat RBCs in a dose-dependent manner. Replacement of the carboxylic group with a phosphoric group also increased the OF in RBCs, whereas substitution of the carboxylic group by a sulfonic, amide or hydroxy group did not affect the OF. Replacement of the benzene nucleus with a cyclohexane ring or a straight hydrocarbon chain with six carbons resulted in a greater increase in OF than that induced by benzoic acid. Introduction of a methyl group, chloride or bromide at the m- and p-positions of the benzene ring considerably enhanced the increase in OF induced by benzoic acid. Substitution of the amino and hydroxy group at the m- and p- positions abolished the increase in OF induced by benzoic acid. The introduction of these elements at the o-position showed an almost equal increase in OF as that observed for benzoic acid. A molecule of benzoic acid is composed of both hydrophilic (carboxylic group) and hydrophobic (benzene ring) components. Replacement of the hydrophilic component changed the balance formed between hydrophobic and hydrophilic components in the moiety, resulting alterations to its interaction with the RBC membrane. The size, form and elements introduced into the benzene ring also affected its affinity to the cell membrane, and changed the osmotic resistance in rat RBCs.