Risk of postpartum disease activity with subcutaneous versus intravenous Natalizumab in pregnant women with multiple...

Intravenous (IV) Natalizumab (NTZ) extended-interval dosing (EID) in women with multiple sclerosis (WwMS) is safe and effective in controlling disease activity during pregnancy. Recently, a subcutaneous (SC) form of the drug has become available.

To assess clinical/radiological relapses in postpartum comparing IV and SC NTZ EID in two groups of pregnant WwMS.

We retrospectively collected data on pregnancies across French and Italian MS centers. We assessed clinical/radiological activity in postpartum, accounting for the number of administrations during pregnancy and the duration of NTZ washout. Fisher's exact test, followed by multivariable logistic regression to adjust for confounders, were used to compare outcomes by administration route. Group differences in the odds of disease activity were expressed as odds ratios (OR).

56 pregnancies were identified (35IV, 21SC). Relapses were rare and not different between groups (p=0.88). Postpartum radiological activity was observed in 10/21 WwMS with SC NTZ (47.6%), versus 5/35 with IV NTZ (14,3%) (p=0.012; OR=5.32[CI:1.41-20.06]). Notably, 50% of all reactivations with SC NTZ occurred with washout between 10 and 12 weeks.

Our study suggests a higher risk of postpartum radiological activity in pregnant WmMS treated with SC NTZ EID, prompting for adaptation of the administration schedule to control disease reactivation.