Determination of Binding Capacity and Affinity Constants of Sevelamer Hydrochloride and its Market Preparation

Abstract

Sevelamer is an orally administered weakly basic anion exchange resin which consists of crosslinked
polymeric amine that binds dietary phosphate in the gastrointestinal tract. This is approved for the treatment
of hyperphosphatemia in adult patients with end-stage renal disease. The binding parameter constants of nonabsorbable
sevelamer in its hydrochloride form were determined using the Langmuir approximation for its active
pharmaceutical ingredient and 400 mg generic tablet dosage form (Sevel) at pH 4.0, 5.5 and 7.0. The binding
parameters were also compared with the innovator product Renagel 400 mg tablet. The results demonstrate the
equivalency of the dosage form at each pH in terms of the in vitro binding parameters. The results also demonstrate
a shift in the binding mechanism from pH 4.0 to 7.0.