Pharmacodynamic testing and new validated HPLC method to assess the interchangeability between multi-source orlistat capsules

Background Orlistat is an irreversible inhibitor of the lipase enzyme that prevents trigylcerides from being digested, thereby inhibiting triglyceride hydrolysis and absorption. The resultant reduced calorie uptake enables a positive effect on weight control. Systemic absorption of the drug is, therefore, not necessary for its mode of action. An alternative in vitro study (pharmacodynamic) has been introduced for this drug, as in vivo bioavailability studies are irrelevant with regard to the achievement of the product's intended purposes. Objectives To develop a new validated high-performance liquid chromatography (HPLC) method for the analysis of orlistat and to assess the potency and equivalence of three orlistat formulations using the pharmacodynamic method as a surrogate indicator of pharmaceutical interchangeability. Methods A new HPLC method was developed for the analysis and for the dissolution studies of orlistat in capsules. Pancreatic lipase activity was measured for three different capsule products: Orlislim®, Slimcare®, and Xenical®, G1, G2, and the brand, respectively. Porcine pancreatic lipase and p-nitrophenyl butyrate (PNPB) were placed in a pH 7.4 reaction buffer at 37°C, and substrate hydrolysis was monitored by measuring absorbance changes at 410 nm; this was repeated on six capsules of each product. The inhibition was expressed by the concentration of product, which inhibited 50% of the activity of pancreatic lipase (IC50). Results The new analytical method was suitable for orlistat analysis. Values of IC50 from regression lines and equations were 6.14, 8.43, and 7.80 μg/mL for Orlislim®, Xenical®, and Slimcare®, respectively. Conclusion Pharmacodynamic studies of lipase inhibition could be used to support in vitro dissolution, which demonstrates interchangeability between generic and branded orlistat capsules. Moreover, it could be suggested as an alternative tool to bioequivalence studies for orlistat oral products.