Impact of granulocytes on the antimicrobial effect of tedizolid in a mouse thigh infection model

Abstract

Tedizolid (TR-700, formerly torezolid) is the active component of the new oxazolidinone prodrug tedizolid phosphate (TR-701). We had previously demonstrated that tedizolid possessed potent antistaphylococcal activity superior to that of linezolid in a neutropenic mouse thigh infection model (A. Louie, W. Liu, R. Kulawy, and G. L. Drusano, Antimicrob. Agents Chemother. 55:3453-3460, 2011). In the current investigation, we used a mouse thigh infection model to delineate the effect of an interaction of TR-700 and granulocytes on staphylococcal cell killing. We compared the antistaphylococcal killing effect of doses of TR-701 equivalent to human exposures ranging from 200 to 3,200 mg/day in both granulocytopenic and normal mice. The mice were evaluated at 24, 48, and 72 h after therapy initiation. In granulocytopenic mice, a clear exposure response in which, depending on the time point of evaluation, stasis was achieved at "human-equivalent" doses of slightly below 2,300 mg/day (at 24 h) to slightly below 2,000 mg/day (at 72 h) was observed. In immune-normal animals, stasis was achieved at human-equivalent doses of slightly greater than 100 mg/day or less. The variance in bacterial cell killing results was attributable to the presence of granulocytes (without drug), the direct effect of TR-700 on Staphylococcus aureus, and the effect of the drug on Staphylococcus aureus mediated through granulocytes. The majority of the bacterial cell killing in normal animals was attributable to the effect of TR-700 mediated through granulocytes. Additional studies need to be undertaken to elucidate the mechanism underlying this observation.

Figures

Fig. 1.

Structures of tedizolid phosphate and tedizolid. (A) Tedizolid phosphate (TR-701 [prodrug]). (B) Tedizolid (TR-700).

Fig. 2.

(A) Colony counts over 72 h of S. aureus in the thighs of granulocytopenic mice. (B) Colony counts over 72 h of S. aureus in the thighs of granulocyte-replete mice.

Fig. 3.

Predicted-observed regression of total colony counts of S. aureus in the thighs of tedizolid phosphate-treated mice (tedizolid-active moiety).

Fig. 4.

(A) Simulation of Staphylococcus aureus growth in the thighs of no-treatment control mice that were granulocytopenic. The solid line represents predicted colony counts. Squares represent observed colony counts. (B) Simulation of Staphylococcus aureus growth in the thighs of no-treatment granulocyte-replete control mice. The solid line represents predicted colony counts. Squares represent observed colony counts.

Fig. 5.

(A) Simulation of Staphylococcus aureus growth in the thighs of granulocytopenic mice that were treated with an exposure to tedizolid equivalent to 200 mg of tedizolid phosphate in humans (AUC0-24 = 20.1 mg·h/liter). The solid line represents predicted colony counts. Squares represent observed colony counts. (B) Simulation of Staphylococcus aureus killing in the thighs of granulocyte-replete mice that were treated with an exposure to tedizolid equivalent to 200 mg of tedizolid phosphate in humans (AUC0-24 = 20.1 mg·h/liter). The solid line represents predicted colony counts. Squares represent observed colony counts.