Improvement of Bioavailability of Poorly Soluble Racecadotril by Solid Dispersion with Surface Adsorption Method: A Case Study

Introduction: Biopharmaceutics classification system class II drugs show unpredictable bioavailability based on their solubility. Unfortunately, very few products were manufactured by this technique owing to their poor flowability and stability. The objective of the current investigation was used to improve the flowability by surface solid dispersion (SSD; SD with surface adsorption technology) and improve the absorption of racecadotril (RT) under low pH conditions (i.e., in stomach) to show anti-diarrheal effect by reducing water and electrolyte secretion into the intestine. 
Materials and Methods: SSDs and physical mixtures (PMs) were prepared using various ratios of hydrophilic carriers (polyethylene glycol 4000, polyethylene glycol 6000, and Gelucire 50/13) and an adsorbent (lactose monohydrate). Fourier-transform infrared spectroscopy, differential scanning calorimetry, X-ray diffractometry , and dissolution studies (in vitro) were conducted to characterize SSDs and PMs. 
Results: Phase solubility curves represent AL type, indicating that the solubility of drug linearly increased with an increase in the concentration of carrier. Characterization studies indicated that no interactions between carrier and drug. Solid-state characterization showed a reduction in crystallinity that further supports increment in solubility and dissolution. The optimized formulation (SDG4) showed 99.84 } 1.5% drug release in 15 min compared to RT plain drug (11.95 } 1.72%). In vivo bioavailability studies of SDG4 revealed a significant (P < 0.05) increase in Cmax 65.38 } 1.34 μg/mL (1.75-fold) with increased relative bioavailability (180.22-fold) against the RT plain drug. 
Conclusion: Formulation of SD with surface adsorption method could enhance solubility, dissolution, and bioavailability of RT.