• Plasma drug concentration parameters: AUC0-24, Cmax [ Time Frame: 13-17 Days ] [ Designated as safety issue: No ]
  

• Adverse events, vital signs, ECGs and laboratory test values [ Time Frame: Day 1 to End of study ] [ Designated as safety issue: No ]
  

This is a prospective, multi-center, open-label, repeat-dose pharmacokinetic study that contains two treatment (micafungin 1.0mg/kg and 1.5mg/kg) dose groups. Subjects will be enrolled according to age and stratified by weight to receive either 1.0mg/kg (weight > 25kg) or 1.5mg/kg ( weight < 25kg) micafungin.

Children (4 months to < 2years, 2 to 5 years and 6 to 11 years) and adolescents (12 to 16 years) undergoing HSCT who require antifungal prophylaxis will be enrolled

Inclusion Criteria:

• Institutional Review Board (IRB)-approved written informed Consent / Assent (as applicable) and HIPAA Authorization must be obtained from the subject (as able) and /or subject's parent/legally authorized representative prior to any study-related procedures
• Subject has sufficient venous access to permit administration of study drug, collect pharmacokinetic samples and monitor laboratory safety variables
• Female subject of childbearing potential must have a negative pregnancy test within 72 hours prior to the first dose of study drug, and if sexually active agree method of birth control per Investigator judgment for the duration of the study
• Subject (when able) and /or subjects parent/legally authorized representative agree to comply with the study requirements and with the concomitant medication restrictions
• Subject plans to undergo a HSCT

Exclusion Criteria:

• Subject has evidence of significant liver disease as defined by aspartate transamine (AST/SGOT), alanine transaminases (ALT/SGPT) 10 times the upper limit of normal (ULN) and total bilirubin or alkaline phosphatase > 5 times the ULN
• Subject has concomitant medical condition that in the opinion of the Investigator and /or medical monitor precludes enrollment into the study
• Subject with evidence of an active systemic or disseminated fungal infection prior to enrollment
• Subject has a history of anaphylaxis, hypersensitivity, or any serious reactions to the echinocandin class of antifungals
• Subject had received treatment with an echinocandin within one week prior to first dose of study drug
• Subject status is unstable and subject is unlikely to complete required study procedures
• Female subject is pregnant or nursing. Females of childbearing potential must avoid becoming pregnant while receiving study drug