Development and Evaluation of Oral Zoledronic Acid with Controlled Release in EC Capsules

Abstract

Introduction: Bisphosphonates are a class of drugs that act as inhibitors for osteoclast-mediated bone resorption and they are widely used in treating patients with osteoporosis. Zoledronic Acid (ZA) is an intravenous (IV) bisphosphonate derivative that was approved by the FDA under trade names Reclast® (intravenous infusion with a dose of 5 mg once yearly) and Zometa® (dose of 4 mg once monthly). However, due to the high potency of ZA, small IV doses with monthly or annual injections are required. IV injection leads to lower patient compliance, furthermore, the requirement of expertise in handling leads to substantial increase in the costs of healthcare. All these shortcomings of the intravenous treatment can be solved via oral administration. However, there are additional challenges involved with the oral route, including drug degradation in acidic gastric fluids, irritation of the intestinal membranes and low drug bioavailability. Therefore, in this study, we proposed to develop an oral formulation of ZA, which confers high protection to the drug against chemical and physical degradation while also demonstrates desired oral bioavailability and a controlled release profile. Aim: To develop a novel ZA loaded oral formulation in order to improve the oral bioavailability of ZA with a controlled release profile and maximize the drug potency. Method: An isocratic reverse phase high performance liquid chromatography (RPHPLC) analytical method for identification and quantification in formulations of ZA, was developed and validated. Nine ZA loaded formulations were developed using two different techniques (fluid bed coating and freezer milling techniques). ZA loaded enteric coated (EC) microparticles were formulated into granules using lactose, chitosan and microcrystalline cellulose (MCC) in four different formulations and the EC microparticles was accomplished by using Eudragit L100-55 in ethanol as a coating solvent. In Freezer milling technique, ZA was loaded into a polymeric matrix of ßglucan and Eudragit L100-55. In both techniques, the final formulations were filled into EC capsules. All formulations were investigated for their in vitro drug release in acidic (pH 1.2) and in buffered (pH 6.5) media, respectively. Result and discussion: The isocratic RP-HPLC analytical method for ZA was developed and validated for linearity, sensitivity, accuracy, precision and robustness. Nine formulations have been characterized. Formulation 8 (F8) of ZA-loaded 1.5% w/v ß-glucan matrix in EC capsules was the optimal formulation with 20 mg ZA per capsule. Investigation of the morphology by Scanning Electron Microscopy (SEM) in F8 formulation showed variable sized microparticles arranged in a matrix collocation. Zeta potential of the microparticles was +2.15 ± 0.23 mV. Fourier transform infrared spectroscopy (FTIR) revealed that there was no characteristic peak for the pure drug when drug loaded microparticles were tested, indicating the drug was trapped within the polymeric matrix. In vitro drug release test for F8 formulation has shown an acceptable controlled release manner from the matrix with 80% drug release over 120 hours of study. The efficiency of EC capsules was revealed by the greater protection of the drug in acidic conditions with a targeted release in pH > 6 in upper intestines. In vitro cytotoxicity study has demonstrated relatively lower toxicity of ZA against human colonic adenocarcinoma cells (Caco-2) either in the presence of the pure drug or drug loaded formulation with cell viability over 95% after 24 hours of incubation at the concentration of 187.5 μg/mL. Conclusion: This research has demonstrated ZA-loaded ß-glucan microparticles filled into EC capsules as an effective system for oral delivery of ZA. This formulation had shown a targeted delivery of the drug at the absorption site. Moreover, the formulation revealed controlled release pattern with the optimum drug release in the pH conditions that mimic the small intestines, therefore maximize the oral bioavailability of ZA and improve its biological effect in the bones.