Chitosan-based buccal mucoadhesive bilayer tablets enhance the bioavailability of tizanidine hydrochloride by bypassing the first-pass metabolism

Abstract

Tizanidine hydrochloride (TZN) is an antimuscarinic agent used in the treatment of pain-related spasms, multiple sclerosis, and stroke-related spasticity. It has low oral bioavailability (40 %) due to excessive first-pass metabolism in the liver. The aim of this project was to enhance the systemic bioavailability of TZN by developing buccal mucoadhesive bilayer tablet formulations using chitosan salts with molecular weights of 136 kDa (7 cP) and 169 kDa (10 cP). Structural characterisation of chitosans and their salts was performed by FTIR, 1H NMR, DSC, TGA, and XRD analyses. Soluble chitosan salts, chitosan glutamate and chitosan chloride, for the adhesive layer, and insoluble ethyl cellulose for the impermeable backing layer were selected as polymers to fabricate the buccal tablets by direct compression method. The tablets containing TZN demonstrated high swelling and good mucoadhesion characteristics as well as released all the drug within 8 h. While TC10, formulated with 10 cP chitosan chloride, showed the highest swelling properties, TG10, prepared with 10 cP chitosan glutamate, exhibited the highest mucoadhesion. Chitosan glutamate tablets (TG7 and TG10) demonstrated better mucoadhesive characteristics and stability than chitosan chloride ones (TC7 and TC10) in the buccal medium based on the results of swelling and drug release studies. The permeability studies performed by Franz diffusion cell demonstrated that the amount of TZN passing through the bovine buccal mucosa was between 13.4 and 14.4 %. Stability studies conducted at 5 ± 2 °C, 25 ± 2 °C and 40 ± 2 °C for 6 months showed that no changes in the content uniformity and pH were observed. The in vivo comparative bioavailability studies in female New Zealand rabbits were performed and TZN-containing buccal mucoadhesive bilayer tablets fabricated with both chloride (TC10) and glutamate (TG10) salts of chitosan demonstrated three times higher bioavailability than the commercial TZN product (Sirdalud® oral tablet) administered by the gastrointestinal route.