The primary purpose of this study is to assess the effect of multiple doses of isavuconazole on the pharmacokinetics (PK) of methadone after single dose administration. The secondary purpose is to assess the safety and tolerability of isavuconazole alone and in combination with methadone.

Inclusion Criteria:

• The subject has a body weight of at least 45 kg and has a body mass index (BMI) of 18 to 32 kg/m2, inclusive
• 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 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 a positive result for hepatitis C antibodies, 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 methadone or the azole class of compounds, or a history of multiple and/or severe allergies to drugs or foods, or a history of severe anaphylactic reactions
• The subject is a smoker (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 acetaminophen up to 2 g/day
• The subject has a recent history (within the last 2 years) of drug or alcohol abuse, or a positive drug and/or alcohol screen