Determination of the salivary retention of hexetidine in-vivo by high-performance liquid chromatography

The non-antibiotic antimicrobial agent hexetidine is widely used at a concentration of 0.1% w/v as an oral rinse to reduce the number of viable microorganisms within the oral cavity. However, following use, the available concentration of hexetidine in the oral cavity declines with time, thus compromising the resultant antimicrobial activity. It is, therefore, desirable to determine the persistence of the agent in the oral cavity by quantification of the drug concentration in saliva, thus enabling prediction of its antimicrobial activity in the oral environment. A rapid reverse-phase HPLC method was therefore developed and validated for hexetidine in aqueous solution (Oraldene) and in saliva samples collected from volunteers post-rinsing with 15 mL of hexetidine oral rinse for 30s. The HPLC assay was sufficiently sensitive to accurately detect hexetidine in saliva up to 25 min after in-vivo use of a commercial oral rinse. Furthermore, it was possible to detect hexetidine below the published minimum inhibitory concentrations (MICs) for a selection of microorganisms. From these data a first-order elimination rate constant of hexetidine from the oral cavity was determined post-rinsing in each of six volunteers. The validated HPLC assay method presented is useful for the assay of hexetidine in the oral cavity both at and below MICs. The first-order elimination rate constant shows significant variation between volunteers.