The purpose of this study is to assess the effect of multiple doses of isavuconazole on the pharmacokinetics of a single dose of dextromethorphan in healthy adult subjects.

Subjects will check-in on Day -1 and remain confined to the clinical unit until Day 13. On the morning of Day 1, subjects will receive a single dose of dextromethorphan. On Days 6 and 7, subjects will receive isavuconazole three times daily (TID) administered approximately 8 hours apart. On Day 8 through 12, subjects will receive isavuconazole once daily (QD). On Day 10, subjects will receive a single dose of dextromethorphan. A follow-up visit will be scheduled on Day 21 (± 2 days).

Inclusion Criteria:

• The subject has a body weight of at least 45.0 kg and has a body mass index (BMI) of 18.0 to 32.0 kg/m2, inclusive
• The subject's 12-lead electrocardiogram (ECG) is normal at Screening and Day -1 or, if abnormal, the abnormality is not clinically significant as determined by the investigator, including a QTcF of 430 msec or less for male or 450 msec or less for female subjects
• The subject's clinical laboratory test results at Screening and Day -1 are within normal limits unless the investigator considers the abnormality to be not clinically significant. Results for aspartate aminotransferase (AST) and alanine aminotransferase (ALT) must be ≤ upper limit of normal, and total bilirubin must be ≤ 1.5 mg/dL
• The female subject agrees to sexual abstinence, or is surgically sterile, postmenopausal (defined as at least 2 years at Screening without menses), or using a medically acceptable double barrier method (e.g. spermicide and diaphragm, or spermicide and condom) to prevent pregnancy and agrees to continue using this method from Screening until 3 weeks after the follow-up visit at the end of the study; and is not lactating or pregnant as documented by negative pregnancy tests at Screening and Day -1
• The male subject agrees to sexual abstinence, is surgically sterile, or is using a medically acceptable method to prevent pregnancy and agrees to continue using this method from Screening until 3 weeks after the follow-up visit at the end of the study

Exclusion Criteria:

• The subject has any clinically significant (as judged by the Investigator) disease history of the following systems: pulmonary, gastrointestinal, cardiovascular (including a history of clinically significant arrhythmia or clinically significant conduction delays on ECG), hepatic, neurological, psychiatric, renal, genitourinary, endocrine, metabolic, dermatologic, immunologic, hematologic, or malignancy excluding non melanoma skin cancer
• The subject has a history of unexplained syncope, cardiac arrest, unexplained cardiac arrhythmia or torsade de pointes, structural heart disease, or family history of Long QT syndrome (suggested by sudden death of a close relative at a young age due to possible or probable cardiac causes)
• The subject has/had a symptomatic, viral, bacterial (including upper respiratory infection), or fungal (non-cutaneous) infection within 1 week prior to clinic check in on Day -1
• The subject has received a vaccination within the last 30 days prior to study drug administration or plans to receive any vaccinations during the study or within 2 weeks after the last dose of study drug
• The subject has a positive result for hepatitis C antibodies or hepatitis B surface antigen at Screening or is known to be positive for human immunodeficiency virus (HIV)
• The subject has a known or suspected allergy to any of the components of the trial products including dextromethorphan or the azole class of compounds, or a history of multiple and/or severe allergies to drugs or foods (as judged by the investigator), or a history of severe anaphylactic reactions
• The subject has smoked (any use of tobacco or nicotine containing products) within 6 months prior to Screening
• The subject has had treatment with prescription drugs or complementary and alternative medicines within 14 days prior to Day -1, or over-the-counter medications within 1 week prior to Day -1, with the exception of occasional use of acetaminophen up to 2 g/day
• The subject has received an experimental agent within 30 days or 5 half-lives, whichever is longer, prior to Day -1
• The subject has had any significant blood loss, donated one unit (450 mL) of blood or more, or received a transfusion of any blood or blood products within 60 days or has donated plasma within 7 days prior to clinic check-in on Day -1
• The subject has taken part in strenuous exercise within 3 days prior to study drug administration
• The subject anticipates an inability to abstain from caffeine or alcohol use for 48 hours prior to clinical check-in on Day -1 and throughout the duration of the study; or from grapefruit, Seville oranges, star fruit, or any products containing these items from 72 hours prior to clinic check-in on Day -1 and throughout the duration of the study
• The subject has a recent history (within the last 2 years) of drug or alcohol abuse, as defined by the investigator, or a positive drug and/or alcohol screen at Screening or Day -1