Oramucosal Delivery of LHRH: Pharmacokinetic Studies of Controlled and Enhanced Transmucosal Permeation

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Abstract
Several transmucosal therapeutic systems (TmTs) were developed to study the enhanced/controlled delivery of luteinizing hormone-releasing hormone (LHRH) through oral mucosae for prolonged periods. TmTs is a track field-shaped bilayer mucoadhesive device consisting of fast-release and sustained-release layers. In vivo evaluations were performed in beagle dogs, and pharmacokinetic profiles were monitored to characterize the transmucosal permeation kinetics of LHRH delivered by the various TmTs formulations containing a stabilizer, cetylpyridinium chloride, and a permeation enhancer, such as bile salts, to enhance the stability and permeability of LHRH. The plasma LHRH concentrations were observed to reach the plateau level within 30 min and were maintained for 2 hr following application of TmTs, in contrast to a rapid elimination profile observed after IV administration. Addition of 5% bile salt into the fast-release layer was observed to produce an enhancement in the absorption rate, higher plateau plasma levels, and greater systemic bioavailability. Addition of pH modifiers was noted to affect the bile salt enhanced transmucosal delivery of LHRH. To prolong the plasma LHRH level, several loading doses of LHRH were incorporated into the sustained-release layer. The plasma levels were sustained and the area under the curve (AUC) values were found to be linearly dependent upon the combined loading doses of LHRH in the fast-release and sustained-release layers. Mucosal irritation was also measured, using buccal mucosa, and results were observed to be low and reversible for the single application. The results indicated that TmTs is relatively safe and capable of achieving enhanced and controlled transmucosal delivery of peptide drugs.

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