Adults and children 12 years and older: 2 teaspoonfuls (10 mL) every 4 to 6 hours, not to exceed 8 teaspoonfuls (40 mL) in 24 hours. Children 6 to under 12 years: 1 teaspoonful (5 mL) every 4 to 6 hours, not to exceed 4 teaspoonfuls (20 mL) in 24 hours. Children 2 to under 6 years: ½ teaspoonful (2.5 mL) every 4 to 6 hours, not to exceed 2 teaspoonfuls.

In vitro experiments were conducted using Sweetana-Grass (Navicyte) vertical diffusion cells to evaluate the effect of directionality, donor concentration and pH on the permeation of hydroxyzine and triprolidine across excised bovine olfactory mucosa. These studies demonstrated that the Jm-s (mucosal-submucosal flux) and Js-m (submucosal-mucosal flux) of hydroxyzine and triprolidine across the olfactory mucosa were linearly dependent upon the donor concentration without any evidence of saturable transport. Hydroxyzine inhibited the efflux of P-gp substrates like etoposide and chlorpheniramine across the olfactory mucosa. Both hydroxyzine and triprolidine reduced the net flux (Js-m-Jm-s) of etoposide with IC50 values of 39.2 and 130.6 microM, respectively. The lipophilicty of these compounds, coupled with their ability to inhibit P-gp, enable them to freely permeate across the olfactory mucosa. Despite the presence of a number of protective barriers such as efflux transporters and metabolizing enzymes in the olfactory system, lipophilic compounds such as hydroxyzine and triprolidine can access the CNS primarily by passive diffusion when administered via the nasal cavity.