The pharmacokinetic (PK) profile of Tysabri in patients has been observed following 1 dose and after 6 consecutive doses. The primary purpose of this study is to observe the PK profile of Tysabri in patients who have been treated with Tysabri for at least 12 months (i.e., after achievement of steady state). To support this investigation, the pharmacodynamic (PD) profile will also be established in this population by assessing α4 integrin saturation.
The dosing regimen will be consistent with the current commercial prescribing information (Tysabri 300 mg IV infusion once a month).
The following participant population will be enrolled:
- Have been treated monthly with Tysabri (natalizumab) for at least 12 months (with the 9 most recent doses received at uninterrupted intervals [i.e., every 28±7 days])
- Currently enrolled in the Tysabri Outreach: United Commitment to Health (TOUCH) Prescribing Program
- Tested negative at any prior evaluation for anti-Tysabri antibodies
- Test negative for antibodies to Tysabri at the Screening Visit
Participants will be asked to provide blood samples over a 28-day period following a scheduled infusion of Tysabri.
The primary objective is to assess the PK profile of Tysabri at steady state. The secondary objective is to assess the PD profile (α4 integrin saturation) of Tysabri at steady state.