Clostridioides difficile ATCC® 43255の芽胞を3000 colony-forming unit (CFU)/mouseで経口投与し、重症CDIマウスモデル（芽胞経口投与後2-3日後に全て死亡）を作製した。作製1日後、24hかけてメトロニダゾール（MNZ）及びバンコマイシン（VCM）を様々な用法用量（MNZ: 5-40 mg/kg × 1-4回 皮下投与、VCM: 40-160 mg/kg × 1-2回 経口投与）で投与した。その糞中pharmacokinetics/pharmacodynamics（PK/PD）パラメータと治療終了時または終了1日後の治療効果（糞中生菌数、芽胞数、生存率及びClinical Sickness Score［CSS］）との関係を評価した。
その結果、VCMにおいて糞中生菌数及び芽胞数の減少は糞中薬物濃度-時間曲線下面積/最小発育阻止濃度（AUC/MIC）と最も相関した（R2 = 0.77、0.75）。生存率及びCSSともAUC/MICは相関し（R2 = 0.59、0.56）、糞中生菌数を ≥5 log10 CFU/g減少させる目標値はAUC/MIC ≥17678となった。この目標値では100%の生存を達成した。本研究よりCDIを治療するための最適なVCM糞中PK/PDパラメータ値はAUC/MIC≧17678であることが示唆された。同様にMNZの糞中PK/PDパラメータ値はAUC/MIC≧274であった。
以上、CDIに対する新規 in vivo PK/PD評価モデルの開発に成功し、MNZ及びVCMの最適な糞中PK/PDパラメータ値を世界で初めて明らかにすることができた。
C57BL/6J female mice were infected by gavage with 3000 colony-forming unit (CFU) of C. difficile ATCC® 43255 spore to establish severe Clostridioides difficile infection (CDI) mouse models. The CDI mouse models completely die by day 3 (72 h after the gavage). Metronidazole (MNZ) and vancomycin (VCM) were respectively administered into CDI mouse models in various dosage regimens (MNZ: 5-40 mg/kg × 1-4 times, S.C., VCM: 40-160 mg/kg × 1-2 times, P.O.) for 24 h from day 1 (24 h after the gavage) to day 2 (48 h after the gavage). After the 24 h treatment, mice were monitored for stool scale, weight loss, behavior, and survival. In addition, fecal samples were collected from dead mice at day 2 or day 3 and survived mice at day 3 to quantify vegetative cells and spore in feces. Then, we evaluated the relationships between fecal pharmacokinetics/pharmacodynamics (PK/PD) indexes and those efficacies after the treatment.
As a result, decreases of vegetative cells and spores were corelated with ratio of the area under the fecal drug concentration–time curve to the minimum inhibitory concentration (AUC/MIC) (R2 = 0.77、0.75), respectively. The AUC/MIC was also corelated with survival rate and clinical sickness score (R2 = 0.59、0.56), respectively. The target value to decrease vegetative cells in feces (≥5 log10 CFU/g) was estimated to be ≥17678. At the target value, 100 % of CDI mouse models were estimated to survive after treatment. These results suggested that an optimal fecal PK/PD index of VCM to treat CDI was AUC/MIC ≥17678. Similarly, the optimal fecal PK/PD index of MNZ was AUC/MIC ≥274.
We successfully developed novel in vivo PK/PD evaluation models against CDI and elucidate optimal fecal PK/PD indexes of MNZ and VCM to treat CDI for the first time.
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