Depot medroxyprogesterone acetate concentrations in patients with and without the use of antiseizure medications.

Objectives: To measure plasma concentrations of medroxyprogesterone acetate (MPA) in users with epilepsy treated with antiseizure medications and compare these to MPA concentrations in those without epilepsy.

Study Design: For this multisite cross-sectional study, we obtained a single blood sample from those with epilepsy treated with various antiseizure medications (n = 18) within the week before their next depot medroxyprogesterone injection. Among the participants without epilepsy (n = 20), 10 similarly were scheduled within the week prior to the next injection, and 10 were scheduled at earlier intervals to attempt to balance the time intervals between groups. MPA concentrations were determined by a validated assay.

Results: MPA concentrations were similar among those with epilepsy and controls and between groups with and without the use of enzyme-inducing medications. The lowest MPA concentrations, under 0.07 ng/mL, were observed among two of eight using enzyme-inducing antiseizure medications, one of 10 using noninducing medications, and one of 19 controls had concentrations below 0.2 ng/mL.

Conclusions: In this exploratory study, lower MPA concentrations in some participants using enzyme-inducing antiseizure medications suggest a potential interaction that could reduce depot medroxyprogesterone efficacy.