Application Site of Transdermal Scopolamine Influences Efficacy and Drug Concentration in Salivary Glands in Rats

Transdermal scopolamine applied to the postauricular area is used to treat drooling. We investigated the duration of action of scopolamine ointment and the effect of the application site on drug efficacy and concentration in the salivary glands of rats. Scopolamine ointment was applied to the skin over the salivary glands (SSG) and back (SB). Saliva volume was measured after intraperitoneal administration of pilocarpine. Blood and salivary glands were collected after scopolamine ointment application, and scopolamine concentrations in the plasma and salivary glands were measured. Saliva volume after application in the SSG group was significantly lower at all time points than in the non-treated group, and the change in saliva volume in the SSG group was greater than that in the SB group at all time points. This suggests that applying scopolamine ointment to the SSG strongly suppresses salivary secretion. Scopolamine concentration in the salivary glands of the SSG group was significantly higher at 9 h. The change in the efficacy of scopolamine ointment depending on the application site was due to the difference in transfer to the salivary glands. Transdermal administration of scopolamine to the skin over the salivary glands may have high efficiency in treating drooling.