Enhanced Oral Bioavailability and Anti-Echinococcosis Efficacy of Albendazole Achieved by Optimizing the "Spring" and "Parachute".

Maximizing the pharmacological efficacy of albendazole (ABZ), an anti-echinococcosis drug, is essential in the long-term treatment of patients with echinococcosis. As a weakly alkaline drug, ABZ has a pH-dependent solubility that decreases dramatically from gastric fluid (pH 1.4) to intestinal fluid (pH 6.5), where it is absorbed. In this study, we endeavored to develop an optimized tablet formulation of ABZ to improve its dissolution and oral bioavailability from two aspects: a faster initial dissolution in the gastric pH condition (i.e., the "spring") and a more prolonged drug supersaturation in the intestinal pH condition (i.e., the "parachute"). To achieve this goal, ABZ-HCl salt was selected first, which demonstrated a higher intrinsic dissolution rate under pH 1.4 compared with the ABZ free base that is used in the commercial product Albenda. Second, by comparing the ABZ supersaturation kinetics under pH 6.5 in the presence of various polymers including poly(vinylpyrrolidone) (PVP), PVP/VA, hydroxypropyl methylcellulose (HPMC), and HPMC acetate succinate (HPMC-AS), HPMC-AS was found to be the most effective crystallization inhibitor for ABZ, likely due to the hydrophobic interaction between ABZ and HPMC-AS in an aqueous environment. The newly designed tablet formulation containing ABZ-HCl and HPMC-AS showed ∼3 times higher oral bioavailability compared with that of Albenda in Beagle dogs. More significantly, the anti-echinococcosis efficacy of the improved formulation was 2.4 times higher than that of Albenda in a secondary hepatic alveolar echinococcosis Sprague-Dawley rat model. The strategy of simultaneously improving the spring and parachute of an oral formulation of ABZ, by using a highly soluble salt and an effective polymeric crystallization inhibitor, was once again proven to be a viable and readily translatable approach to optimize the unsatisfactory oral medicines due to solubility and bioavailability limitations.