Objectives: Isavuconazole is a convenient triazole antifungal agent with a broad antifungal spectrum. A randomized, open-label study (ClinicalTrials.gov, NCT03471988) was conducted to evaluate the efficacy and safety of isavuconazole in Japanese patients with deep-seated mycoses., Patients and Methods: In Cohort A, patients with aspergillosis (chronic pulmonary aspergillosis and invasive aspergillosis) were randomized in a 2:1 ratio to isavuconazole or voriconazole, and in Cohort B, patients with cryptococcosis and mucormycosis were assigned to isavuconazole for up to 84 days of treatment. The overall outcome was evaluated according to the clinical, radiological, and mycological responses at Days 42 and 84 and at the end of treatment (EOT)., Results: A total of 103 participants were enrolled and received the study drug. The overall response rate of patients with chronic pulmonary aspergillosis in the isavuconazole (52 patients) and voriconazole (27 patients) groups was 82.7% and 77.8% at EOT, respectively. The response rate in patients with cryptococcosis (10 patients, isavuconazole group only) was 90.0%. One of three participants with invasive aspergillosis and one of three participants with mucormycosis responded in the isavuconazole group. In the safety evaluation, the incidence of adverse events in participants with chronic pulmonary aspergillosis was similar in both groups. Adverse drug reactions were reported in 32 (61.5%) patients receiving isavuconazole and 23 (85.2%) patients receiving voriconazole., Conclusions: Isavuconazole showed efficacy and safety in Japanese patients with chronic pulmonary aspergillosis and cryptococcosis, for which the drug is not currently indicated., Competing Interests: Declaration of competing interest K.I. has received financial support for the present manuscript from Asahi Kasei Pharma Corporation; grants, consulting fees, and honoraria from Asahi Kasei Pharma Corporation, and honoraria from Pfizer, outside the submitted work. T.T. has received non-financial support for the present manuscript from Asahi Kasei Pharma Corporation; grants from MSD, Sumitomo Dainippon Pharma, Takeda Pharmaceutical, and Shionogi Pharma; honoraria from Sumitomo Dainippon Pharma, Pfizer, Kyorin Pharmaceutical, Fisher & Paykel Healthcare, and MSD; and participated on the advisory boards of GlaxoSmithKline, Roche Diagnostics, and Pfizer, outside the submitted work. T.M. has received non-financial support for the present manuscript from Asahi Kasei Pharma Corporation; grants from Asahi Kasei Pharma Corporation, Pfizer, MSD, Astellas Pharma, Otsuka Pharmaceutical, Taisho Pharmaceutical, Daiichi Sankyo, Teijin Pharma, Mitsubishi Tanabe Pharma, Shionogi Pharma, Kyowa Kirin, Chugai Pharmaceutical, and AbbVie; consulting fees from Asahi Kasei Pharma Corporation, Pfizer, and Kyorin Pharmaceutical; honoraria and support for attending meetings from Asahi Kasei Pharma Corporation, Pfizer, MSD, Astellas Pharma, Sumitomo Dainippon Pharma, Janssen Pharmaceutical, AstraZeneca, GlaxoSmithKline, Taisho Pharmaceutical, Daiichi Sankyo, Meiji Seika Pharma, Eli Lilly, Novartis Pharma, Boehringer Ingelheim, Shionogi Pharma, Takeda Pharmaceutical, Gilead Sciences, Insmed, and Sanofi; and drugs and medical writing services from Pfizer and MSD, outside the submitted work. K.K. was a member of the Data Review Committee for Asahi Kasei Pharma Corporation during the conduct of the study; K.K. has received grants from Asahi Kasei Pharma Corporation, Sumitomo Dainippon Pharma, and MSD, outside the submitted work. K.A. has received grants from Asahi Kasei Pharma Corporation, Sumitomo Dainippon Pharma, and Takeda Pharmaceutical, and honoraria from Pfizer and Janssen Pharmaceutical, outside the submitted work. H.M. has received consulting fees and honoraria from Asahi Kasei Pharma Corporation, outside the submitted work. F.O. was a member of the Data Review Committee for Asahi Kasei Pharma Corporation during the conduct of the study; F.O. has received consulting fees from Asahi Kasei Pharma Corporation, outside the submitted work. Y.K. has received grants from Asahi Kasei Pharma Corporation, Sumitomo Dainippon Pharma, and Pfizer, and honoraria from Asahi Kasei Pharma Corporation, Sumitomo Dainippon Pharma, Pfizer, MSD, Astellas Pharma, and Janssen Pharmaceutical, outside the submitted work. H.K. was a member of the Data Review Committee for Asahi Kasei Pharma Corporation during the conduct of the study; H.K. has received honoraria from MSD, Sumitomo Dainippon Pharma, Astellas Pharma, Pfizer, and Shionogi Pharma, outside the submitted work. S.K. was a member of the Data Review Committee for Asahi Kasei Pharma Corporation during the conduct of the study; S.K. has received consulting fees from Asahi Kasei Pharma Corporation, and honoraria from MSD, Sumitomo Dainippon Pharma, Pfizer, Bristol-Myers Squibb, Eisai, Takeda Pharmaceutical, Janssen Pharmaceutical, Meiji Seika Pharma, Astellas Pharma, Kyowa Kirin, Chugai Pharmaceutical, Ono Pharmaceutical, Nippon Kayaku, SymBio Pharmaceuticals, and Nippon Shinyaku, outside the submitted work. M.K. is an employee and stockholder of Asahi Kasei Pharma Corporation; M.K. also has patent 2021-157676 pending with Asahi Kasei Pharma Corporation. M.M. is an employee of Asahi Kasei Pharma Corporation; M.M. also has patent 2021-157676 pending with Asahi Kasei Pharma Corporation. Y.N. was a member of the Data Review Committee for Asahi Kasei Pharma Corporation during the conduct of the study; Y.N. has received consulting fees from Asahi Kasei Pharma Corporation, outside the submitted work. All other authors: none to declare., (Copyright © 2022 Japanese Society of Chemotherapy and The Japanese Association for Infectious Diseases. Published by Elsevier Ltd. All rights reserved.)