LAUSR

Graphical abstract Figure. No Caption available. Abstract Etilefrine hydrochloride (ET‐HCl) is used in the treatment of hypotension. Dosage forms of orally administered tablets and parenteral injections are clinically available, but exhibit unfavorable characteristics, including cardiac toxicity, headaches, and damage at the injection site for the parenteral dosage form, and initially high plasma levels, fast elimination, and first‐pass effects for its oral administration. Therefore, the buccal application of ET‐HCl was herein investigated as an alternative to conventional administration routes. I.v., intragastric, and buccal administration were performed using rats, and absorption features were compared. Buccal application at open conditions for 1 h exhibited absolute bioavailability of more than 20%, while the intragastric administration gave much lower bioavailability (<10%). The drug residue and drug distribution in the oral mucosa were investigated in order to clarify drug transfer behaviors. In the application of ET‐HCl solution using a cotton ball, higher plasma concentrations and their maintenance at higher levels were achieved at 10 mg/kg than at 2.5 mg/kg. In addition, absorption was greater with a longer application (4 h) than with a shorter application (1 h). Etilefrine (ET) was rapidly absorbed using aqueous buffer of pH 9.5 as the solvent. Open application was appropriate for achieving and maintaining higher plasma levels. Thus, in the buccal application of ET‐HCl aqueous droplets, a wide distribution throughout the mucosal surface is important for achieving rapid absorption and the maintenance of plasma levels. These findings suggested that the buccal application should be feasible administration of ET‐HCl.