Improvement of Oral Bioavailability of Lopinavir Without Co-administration of Ritonavir Using Microspheres of Thiolated Xyloglucan

Lopinavir is a BCS Class IV drug exhibiting poor bioavailability due to P-gp efflux and limited permeation. The aim of this research was to formulate and characterize microspheres of lopinavir using thiolated xyloglucan (TH-MPs) as carrier to improve its oral bioavailability without co-administration of ritonavir. Thiomeric microspheres were prepared by ionotropic gelation between alginic acid and calcium ions. Interaction studies were performed using Fourier transform infrared spectroscopy (FT-IR). The thiomeric microspheres were characterized for its entrapment efficiency, T80, surface morphology, and mucoadhesion employing in vitro wash off test. The microspheres were optimized by 32 factorial design. The optimized thiomeric microsphere formulation revealed 93.12% entrapment efficiency, time for 80% drug release (T80) of 358.1 min, and 88% mucoadhesion after 1 h. The permeation of lopinavir from microspheres was enhanced 3.15 times as determined by ex vivo study using everted chick intestine and increased relative bioavailability over 3.22-fold over combination of lopinavir and ritonavir as determined by in vivo study in rat model.