BAX 855 PK-guided Dosing

1. To compare the efficacy and safety of pharmacokinetic (PK)-guided treatment with BAX 855 targeting FVIII trough levels of 1-3% and approximately 10% (8-12%)
2. To further characterize pharmacokinetic (PK) and pharmacodynamic (PD) parameters of BAX 855


Eligibility Criteria:
INCLUSION CRITERIA:

* Participants transitioning from another BAX 855 study who meet ALL of the following criteria are eligible for this study:

  1. Participant has completed the end of study visit of a BAX 855 study or is transitioning from the ongoing Baxalta Continuation Study 261302.
  2. Participant is either receiving on-demand treatment or prophylactic treatment with BAX 855 and had an Annual Bleed Rate (ABR) of ≥ 2 documented and treated during the past 12 months.
  3. Participant is human immunodeficiency virus negative (HIV-); or HIV+ with stable disease and CD4+ count ≥ 200 cells/mm\^3, as confirmed by central laboratory.
  4. Participant is willing and able to comply with the requirements of the protocol.
* Newly recruited participants (ie not transitioning from another BAX 855 study) including BAX855 naïve participants who meet ALL of the following criteria are eligible for this study:

  1. Participant has severe hemophilia A (FVIII clotting activity \< 1%) as confirmed by central laboratory OR by historically documented FVIII clotting activity performed by a certified clinical laboratory, optionally supported by a FVIII gene mutation consistent with severe hemophilia A
  2. Participant has been previously treated with plasma-derived FVIII concentrates or recombinant FVIII for ≥ 150 documented exposure days (EDs)
  3. Participant is either receiving on-demand treatment or prophylactic treatment and had an annual bleeding rate of ≥ 2 documented and treated during the past 12 months.
  4. Participant has a Karnofsky performance score of ≥ 60 at screening
  5. Participant is HIV-; or HIV+ with stable disease and CD4+ count ≥ 200 cells/mm\^3, as confirmed by central laboratory at screening
  6. Participant is hepatitis C virus negative (HCV-) by antibody (if positive, additional PCR testing will be performed), as confirmed by central laboratory at screening; or HCV+ with chronic stable hepatitis
  7. If female of childbearing potential, participant presents with a negative urine pregnancy test and agrees to employ adequate birth control measures for the duration of the study
  8. Participant is willing and able to comply with the requirements of the protocol.

EXCLUSION CRITERIA:

* Participants transitioning from another BAX 855 study who meet ANY of the following criteria are not eligible for this study:

  1. Participant has developed a confirmed inhibitory antibody to FVIII with a titer of ≥ 0.6 BU using the Nijmegen modification of the Bethesda assay as determined at the central laboratory during the course of the previous BAX 855 study.
  2. Participant has been diagnosed with an acquired hemostatic defect other than hemophilia A.
  3. The participant's weight is \< 35 kg or \> 100 kg.
  4. Participant's platelet count is \< 100,000/mL.
  5. Participant has an abnormal renal function (serum creatinine \> 1.5 times the upper limit of normal).
  6. Participant has active hepatic disease with alanine aminotransferase (ALT) and/or aspartate aminotransferase (AST) levels ≥ 5 times the upper limit of normal.
  7. Participant is scheduled to receive a systemic immunomodulating drug (e.g. corticosteroid agents at a dose equivalent to hydrocortisone greater than 10 mg/day, or α-interferon) other than anti-retroviral chemotherapy during the study.
  8. Participant has a clinically significant medical, psychiatric, or cognitive illness, or recreational drug/alcohol use that, in the opinion of the investigator, would affect participant's safety or compliance.
  9. Participant is planning to take part in any other clinical study during the course of the study.
  10. Participant is a member of the team conducting this study or is in a dependent relationship with one of the study team members. Dependent relationships include close relatives (ie, children, partner/spouse, siblings, parents) as well as employees of the investigator or site personnel conducting the study.

Newly recruited participants (ie not transitioning from another BAX 855 study) who meet ANY of the following criteria are not eligible for this study:

1. Participant has detectable FVIII inhibitory antibodies (≥ 0.6 BU using the Nijmegen modification of the Bethesda assay) as confirmed by central laboratory at screening.
2. Participant has a history of confirmed FVIII inhibitors with a titer ≥ 0.6 Bethesda Units (BU) (as determined by the Nijmegen modification of the Bethesda assay or the assay employed with the respective cut-off in the local laboratory) at any time prior to screening.
3. Participant has been diagnosed with an inherited or acquired hemostatic defect other than hemophilia A (eg, qualitative platelet defect or von Willebrand's disease).
4. The participant's weight is \< 35 kg or \> 100 kg.
5. Participant's platelet count is \< 100,000/mL.
6. Participant has known hypersensitivity towards mouse or hamster proteins, PEG or Tween 80.
7. Participant has severe chronic hepatic dysfunction \[eg, ≥ 5 times upper limit of normal alanine aminotransferase (ALT) and/or aspartate aminotransferase (AST), as confirmed by central laboratory at screening, or a documented INR \> 1.5\].
8. Participant has severe renal impairment (serum creatinine \> 1.5 times the upper limit of normal).
9. Participant has current or recent (\< 30 days) use of other pegylated drugs prior to study participation or is scheduled to use such drugs during study participation.
10. Participant is scheduled to receive during the course of the study, a systemic immunomodulating drug (e.g. corticosteroid agents at a dose equivalent to hydrocortisone greater than 10 mg/day, or α-interferon) other than anti-retroviral chemotherapy.
11. Participant has participated in another clinical study involving an IP or investigational device within 30 days prior to enrollment or is scheduled to participate in another clinical study involving an IP or investigational device during the course of this study.
12. Participant has a medical, psychiatric, or cognitive illness or recreational drug/alcohol use that, in the opinion of the investigator, would affect participant safety or compliance.
13. Participant is a member of the team conducting this study or is in a dependent relationship with one of the study team members. Dependent relationships include close relatives (ie, children, partner/spouse, siblings, parents) as well as employees of the investigator or site personnel conducting the study.