Study to be redesigned.

The purpose of this study is to learn more about the safety and dosing of rifampin in infants.

Pharmacokinetics and safety of rifampin will be studied in term and preterm infants who are receiving rifampin per standard of care.

Cohort 1:

• Suspected systemic infection
• Infant < 121 days of age at the time of 1st dose of rifampin administration
• Sufficient intravascular access (either peripheral or central) to receive rifampin.

Cohort 2:

• Receiving rifampin per local standard of care.
• Infant < 121 days of age at the time of 1st dose of rifampin administration

Exclusion Criteria:

Cohort 1:

• History of allergic reactions to rifampin
• Aspartate aminotransferase (AST) greater than 3 times upper limit of normal
• Alanine aminotransferase (ALT) greater than 3 times upper limit of normal
• Serum creatinine greater than 1.7 mg.dL
• Urine output < 0.5 mL/hr/kg over the prior 24 hours
• Any condition which would make the subject, in the opinion of the investigator, unsuitable for the study

Cohort 2:

• None