Unexpectedly high exposure to enteric-coated mycophenolate sodium upon once-daily dosing

Enteric-coated mycophenolate sodium (EC-MPS) has a mean half-life of 11.7 hours, which encouraged hope of using this drug once daily in a nonadherent adolescent SLE patient. This is a case report on a 17-year-old adolescent with a history of noncompliance who was switched from twice-daily mycophenolate mofetil (MMF) to once-daily EC-MPS. The EC-MPS dose was equimolar to the daily MMF dose (1 g MMF BID and 1.44 g of EC-MPS OD). The active compound of both drugs, mycophenolic acid, was measured using a commercially available EMIT assay. Both drugs were well-tolerated and maintained remission of the SLE. The average of three 12-hour areas under the time-concentration curves (AUC) on 1 g of MMF BID was 59.0 mgxh/L. In contrast, the 24-hour AUC after 1.44 g EC-MPS OD was 283.2 mgxh/L, more than double the expected 118.0 mgxh/L of two MMF dosing intervals. A repeat 24-hour AUC after 1.08 g of EC-MPS was 218.2 mgxh/L. EC-MPS once daily may be a well-tolerated therapeutic option for nonadherent adolescent lupus patients, but may be associated with a significantly higher exposure than the equivalent MMF BID dose.