Abstract

Introduction: Sodium Risedronate (SR) is a member of bisphosphonate drugs used for osteoporosis treatment. Albeit its well-known 
efficacy, SR suffers from low oral absorption (only 0.63%) and many adverse effects. 
The aim of the study: formulate and characterize oil-in-water microemulsion systems for the oral delivery of SR. 
Methods: Sunflower oil was used for the oil phase. Next, the solubility of SR in different surfactants and co-surfactants was detected. 
Three different ratios of (Tween 80/glycerin) microemulsions were studied: (2/1), (1/1), and (1/2). Regarding SR microemulsions, three 
different formulations: (2/1), (1/1), and (1/2) (Tween 80/glycerin) were characterized for their: transparency, conductivity, light 
transmission, refractive index, droplet size, dissolution tests, and intensive stability studies. 
Results: As Tween 80 and glycerin were the best surfactant/co-surfactant mixture, the higher surfactant ratio (Tween 80) had the largest 
microemulsion region in pseudo-ternary diagrams and a new detected phase (gels). SR microemulsions were transparent liquids of the 
o/w type. (2/1) formulation had the smallest droplet size (8nm) with good stability results across three diverse protocols. Followed by 
the (1/1) formulation (10.89 nm), though this formulation showed an overloading problem (0.4% SR) in stability tests. (1/2) formulation 
(19.21 nm) had the highest loading capacity (0.6% SR). 
Conclusion: The outstanding stability of the (2/1) (0.1% SR) formulation as a highly stable finished drug form or a potential step for 
further formulation development, along with the notable drug loading capacity of the (1/2) (0.6% SR) formulation, emphasize the 
significance of further studies to validate their efficacy and potentials.