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Comparison of various mucoadhesive gelling agents fordevelopment of an immunosuppressant for the oral cavity

Affiliation
Department of Pharmaceutical Technology, Eberhard Karls University Tuebingen, Auf der Morgenstelle 8, 72076 Tuebingen, Germany
Hoffreiter, Alexander;
Affiliation
Department of Pharmaceutical Technology, Eberhard Karls University Tuebingen, Auf der Morgenstelle 8, 72076 Tuebingen, Germany
Lunter, Dominique Jasmin

Tacrolimus (FK 506) is a potent immunosuppressive agent used in the treatment of many immunogenic diseases (e.g. orally administered for the prevention of transplant rejection or as an ointment against immunogenic skin reactions). Immunosuppression is also required in the oral cavity to combat oral lichen planus or severe gingivitis, among others. Orally administered FK 506 exhibits several severe adverse drug reactions due to systemic effects and the ointment intended for dermal use cannot be applied to the buccal mucosa due to its hydrophobicity. Unfortunately, no preparation for buccal use exists on the market, yet. Therefore, a semi-solid mucoadhesive formulation intended to provide a local effect to the buccal mucosa was developed. Due to Tacrolimus being expensive, in order to carry out many preliminary tests ibuprofen (IBU) was chosen as model active due to its similarly poor water solubility and comparable logP value. To evaluate the suitability of different gelling agents, chitosan as a positively, hydroxypropyl methylcellulose (HPMC) as an uncharged and carbomer as negatively charged mucoadhesive polymer were used. Mucosa from porcine esophagus was used as a surrogate for buccal human mucosa due to their similar composition in the mucosa layer. The formulations were prepared with the gelling agents and IBU as suspension gels. Exact IBU concentration in the samples was measured by HPLC. A material tester was successfully used to test force and work of adhesion to the mucosa. Furthermore, a custom-made cell with a defined artificial saliva flow rate was used to test resistance against saliva. To enable systematic comparison of adhesion and mucoadhesion between chitosan, HPMC and carbomer, gels with the same zero shear viscosity were tested. Finally, a formulation with optimal mucoadhesion was obtained.

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