Evaluation of natalizumab pharmacokinetics and pharmacodynamics with standard and extended interval dosing

Backgound: Natalizumab (NTZ) is a highly efficacious therapeutic for multiple sclerosis (MS), but treatment is associated with an increased risk of progressive multifocal leukoencephalopathy (PML). Extended interval dosing (EID) of NTZ has been proposed as an alternative dosing strategy to reduce PML risk. Pharmacokinetic (PK) and pharmacodynamic (PD) profiles of standard interval dosing (SID) and EID under real-world circumstances remain poorly characterized. Objective: To evaluate PK and PD parameters of NTZ for SID and EID in the context of patient and treatment characteristics. Methods: An observational cohort study was conducted to measure NTZ serum concentrations in MS patients at SID and EID nadir timepoints. NTZ occupancy of alpha 4-integrin receptor sites, and cell surface expression of alpha 4-integrin, was also measured. Patient body weight, age, and treatment exposure metrics were collected. Results: NTZ serum concentrations were lower for EID than SID (mean = 18.2 versus 35.7 mu g/ml, respectively; p < 0.001). Patient body weight, age, and treatment duration impacted concentrations with SID, though their influences were reduced or absent with EID. alpha 4-integrin receptor occupancy by NTZ was lower for EID than SID (mean = 78.2 versus 87.4%, respectively; p < 0.001). Body weight impacted alpha 4-integrin receptor occupancy differentially for EID versus SID. alpha 4-integrin cell surface expression was modestly higher for EID than SID (267.2 versus 238.1 MFI, respectively; p < 0.001). Conclusions: EID of NTZ reduces nadir serum drug levels and alpha 4-integrin receptor occupancy, as well as increases alpha 4-integrin cell surface expression. The resulting increase in the number of open alpha 4-intregrin receptors may enhance immune surveillance of JCV and prevention of PML. Body weight plays a significant role in the pharmacokinetic and pharmacodynamic responses to NTZ treatment. Further research is warranted to help establish pharmacological thresholds of NTZ efficacy and safety, which could help guide decision-making for dosing of NTZ.