There are few reports of direct assessment of the percent duration of the dosing interval for which the concentration of the antibiotic in the blood remains above the minimum inhibitory concentration (MIC) (time above the MIC% [%fT>MIC]) and the clinical outcome for piperacillin (PIPC). Therefore, we investigated the relationship between the %fT>MIC and the outcomes in patients receiving PIPC therapy. In patients treated with PIPC at Kitasato University East Hospital, the %fT >MIC for the antibiotic was determined retrospectively for each patient from the serum concentrations of the drug plotted over time, and the relationship between the %fT>MIC and the therapeutic response rate was calculated by logistic regression analysis. Evaluation of the efficacy of the drug was carried out on the basis of its bacteriological effects (elimination of the bacterial pathogen). The analysis revealed that a response rate of >90% was achieved when the %fT>MIC was ≥60%. Assessment of the relationship between the emergence of resistant organisms and the %fT>MIC in the non-responders revealed that the emergence of resistant organisms can be prevented if a %fT>MIC of 60% can be achieved, at which the drug is known to exert maximal bactericidal effect. In conclusion, this study suggested that maintaining the %fT>MIC at a target of 60% in the dosage design of PIPC therapy would result in improved clinical outcomes.

カナマイシン（KM）は，科学的研究インフラが不十分であった時代に，僅か2年で発見から医薬品認可まで到達した奇跡の抗生物質である。本稿では，KMの発見に至る研究動向，KMの基礎・臨床評価，および発見者である梅澤濱夫先生の日本学士院賞受賞と文化勲章受章について記録に基づき概説する。

今年（平成29年）は，カナマイシン（Kanamycin; KM）の発見（1957年）から60年（還暦）に当たることを知らされました。梅澤濱夫先生とともにKM生産放線菌（Streptomyces kanamyceticus）の新種命名者として名を連ねた幸運者である私にとってたいへん深い感慨が湧いています。高齢（1924年生，93歳）のゆえ記憶にいささか心許ないところがありますが，当時のことを思い出すままに書き綴ってみたいと思います。