Protocol opened to recruitment in Nov 2009. No potential subjects identified in 5 years; therefore, study was terminated in Jul 2014 due to lack of feasibility

This is a Phase IV study to evaluate eltrombopag concentrations in breast milk of nursing mothers taking marketed eltrombopag (PROMACTA®). Up to 10 subjects (mother-infant pairs) at as many as 10 study centers in the US will be enrolled. Nursing mothers who are registered with the PROMACTA Pregnancy Registry will be offered the option to participate in this trial if they continue to take commercial eltrombopag post-delivery and decide to breastfeed their infant. Information will be collected in a diary. Breast milk samples will be collected before and after infant feedings for a 24 hour period after eltrombopag dosing to evaluate the eltrombopag concentrations in the breast milk. Mothers will also be given the option to have a pharmacokinetic (PK) blood sample collected from the infant.

Inclusion Criteria:

• Mother is registered with the PROMACTA Pregnancy Registry and meets all the enrollment criteria defined in the PROMACTA Pregnancy Registry study (113327).
• Mother is continuing to take eltrombopag.
• Mother has received 7 consecutive eltrombopag doses prior to the milk sample collection.
• Infant is 4 weeks to 26 weeks of age at the time of milk sampling.
• Exclusively breastfeeding mother-infant pair; either via breast or with expressed milk from the mother.
• Mother is capable of giving written informed consent, which includes compliance with the requirements and restrictions listed in the consent form.

Exclusion Criteria:

• Infant was born with complications that could impact ability to participate in this study.
• Breastfeeding is not well established in the mother-infant pair (e.g., poor latching of the infant or low milk supply).
• Infants who are supplemented with formula or are consuming solid foods.
• Unwillingness or inability of mother to follow the procedures outlined in the protocol.
• Mother is mentally or legally incapacitated