Evaluation of Argatroban Injection in Pediatric Patients Requiring Anticoagulant Alternatives to Heparin

Criteria for Inclusion: * Males and females ages birth to 16 years,inclusive, at enrollment. For neonates, the minimum corrected gestational age should be 37 weeks. * Documented HIT defined as a fall in platelet count to less than 100,000/uL or a \>=50% decrease in platelets after the initiation of heparin therapy with no apparent explanation other than HIT, or * Require anticoagulation and have a documented history of a positive HIT test in the absence of current thrombocytopenia (i.e. patients at risk for HIT), or * In the opinion of the investigator, require alternative anticoagulation due to an underlying condition, such as AT-III deficiency or heparin resistance. * Signed (written) informed consent or assent by the patient (if age appropriate) and the patient's parent or guardian. Criteria for Exclusion: * Any condition which, in the investigator's opinion, would contraindicate the use of Argatroban or would endanger the patient if he/she participated in this trial. * Unexplained aPTT \> 2 times the upper limit of normal at baseline, in the absence of heparin. * International Normalized Ratio (INR) \>1.6 at baseline in the absence of warfarin. * Known clinical site of bleeding or predisposition to bleeding (e.g., GI bleed, hematuria, hemorrhagic CVA,retroperitoneal hematoma, diabetic retinopathy, hemorrhagic pericardial effusion, or hemorrhagic pleural effusion. Patients who have a known clinical site of bleeding may be enrolled if the investigator deems the risk of c…