A Study Evaluating the Safety and Efficacy of Long-term Dosing of Romiplostim in Thrombocytopenic Pediatric Subjects With Immune (Idiopathic) Thrombocytopenia Purpura

• Platelet response to romiplostim defined as platelet counts 50x109/L in the absence of rescue medication. [ Time Frame: 5 years ] [ Designated as safety issue: No ]
• The prevalence of concurrent ITP therapy use over time (corticosteroids, danazol, azathioprine, etc.). [ Time Frame: 5 years ] [ Designated as safety issue: No ]

• Platelet response to romiplostim defined as platelet counts 50x109/L in the absence of rescue medication. [ Time Frame: 3 years ] [ Designated as safety issue: No ]
• The prevalence of concurrent ITP therapy use over time (corticosteroids, danazol, or azathioprine). [ Time Frame: 3 years ] [ Designated as safety issue: No ]

This is an extension study designed to assess the safety and durability of platelet count increases with romiplostim treatment of thrombocytopenic subjects with Immune (Idiopathic) Thrombocytopenia Purpura. This study is available to pediatric subjects who have completed a previous romiplostim ITP study and meet the eligibility criteria of this study.

Inclusion Criteria:

• Subject or subject's legally acceptable representative has provided informed consent.
• Subject completed a romiplostim study for the treatment of thrombocytopenia in pediatric subjects with ITP.

Exclusion Criteria:

• Subject has or previously had any bone marrow stem cell disorder (any abnormal bone marrow findings other than those typical of ITP must be approved by Amgen before a subject may be enrolled in the study).
• Subject has any new active malignancy diagnosed since enrollment in the previous romiplostim ITP study.
• Subject received any alkylating agents within four weeks before the screening visit or anticipated use during the time of the proposed study.
• Other investigational medications are excluded.
• Currently enrolled in another investigational device or drug study, or less than 30 days since ending another investigational device or drug study(s), or receiving other investigational agent(s) (with the exception of romiplostim in a previous clinical study).
• Female subject of child bearing potential (defined as having first menses) is not willing to use highly effective contraception during treatment and for 4 weeks after the end of treatment.
• Female subject is pregnant or breast feeding, or planning to become pregnant within 4 weeks after the end of treatment.
• Subject has known sensitivity to any of the products to be administered during dosing.
• Subject previously has entered this study (this will depend on the type of study).
• Subject will not be available for protocol required study visits, to the best of the subject and investigator's knowledge.
• Subject has any kind of disorder that, in the opinion of the investigator, may compromise the ability of the subject to give written informed consent and/or to comply with all required study procedures.