A Study of Intravenous and Oral Isavuconazonium Sulfate in Pediatric Patients

Inclusion Criteria: * Subject has sufficient venous access to permit administration of study drug (for the IV cohorts), collection of pharmacokinetic samples and monitoring of safety laboratories. * Female subject must either: * Be of non-childbearing potential: Clearly premenarchal or documented surgically sterile * Or, if of childbearing potential: Agree not to try to become pregnant during the study and for 28 days after the final study drug administration; and have a negative urine or serum pregnancy test at screening; and, if heterosexually active, agree to consistently use 2 forms of highly effective birth control (at least one of which must be a barrier method) starting at screening and throughout the study and for 28 days after the final study drug administration. * Female subject who is of childbearing potential must agree not to breastfeed starting at screening and throughout the study and for 28 days after the final study drug administration. * Female subject who is of childbearing potential must not donate ova starting at screening and throughout the study and for 28 days after the final study drug administration. * Male subject who is of childbearing potential and their female spouse/partner who is of childbearing potential must be using highly effective contraception consisting of 2 forms of birth control (at least one of which must be a barrier method) starting at screening and continue throughout the study, and for 90 days after the final study drug administration. * Male subject who is of childbearing potential must not donate sperm starting at screening and throughout the study and, for 90 days after the final study drug administration. * Subject and subject's parent(s) or legal guardian agree that the subject will not participate in another interventional study while on treatment. * For oral cohorts: subject is able to swallow the oral capsule medication. Exclusion Criteria: * Subject has familial short QT syndrome, is receiving medications that are known to shorten the QT interval, or has a clinically significant abnormal electrocardiogram (ECG). * Subject has evidence of hepatic dysfunction defined as: * Total bilirubin ≥ 3 times the upper limit of normal (ULN) * Alanine transaminase or aspartate transaminase ≥ 5 times the ULN * Known cirrhosis or chronic hepatic failure * Subject has used strong cytochrome P450 (CYP) 3A4 inhibitors or inducers such as ketoconazole, rifampin/rifampicin, long acting barbiturates, carbamazepine and St. John's wort in the 5 days prior to the first administration of study drug. * Subject has known history of allergy, hypersensitivity, or any serious reaction to any of the azole class antifungals. * Subject has any condition which makes the subject unsuitable for study participation. * Subject is unlikely to survive 30 days. * Subject has received investigational therapy, with the exception of oncology drug trials, within 28 days or 5 half-lives, whichever is longer, prior to screening. * For oral cohorts: The subject has gastrointestinal disease or has had a procedure that is expected to interfere with the oral absorption or tolerance of the study drug (e.g., functionally relevant gastrointestinal obstruction, mucositis/stomatitis, or frequent vomiting). * Subject previously dosed with isavuconazonium sulfate.