Absorption of cinnarizine from type II lipid-based formulations: Impact of lipid chain length, supersaturation, digestion, and precipitation inhibition.

Lipid-based formulations (LBFs) are an enabling-formulation approach for lipophilic poorly water-soluble compounds. In LBFs, drugs are commonly pre-dissolved in lipids, and/or surfactants/cosolvents, hereby avoiding the rate-limiting dissolution step. According to the Lipid formulation classification system, proposed by Pouton in 2006, in type II LBFs a surfactant with an HLB-value lower than 12 is added to the lipids. If high drug doses are required, e.g. for preclinical toxicity studies, supersaturated LBFs prepared at elevated temperatures may be a possibility to increase drug exposure. In the present study, the impact of digestion on drug absorption in rats was studied by pre-dosing of the lipase inhibitor orlistat. The lipid chain length of the type II LBFs was varied by administration of a medium-chain- (MC) and a long-chain (LC)-based formulation. Different drug doses, both non-supersaturated and supersaturated, were applied. Due to an inherent precipitation tendency of cinnarizine in supersaturated LBFs, the effect of the addition of the precipitation inhibitor Soluplus® was also investigated. The pharmacokinetic results were also evaluated by multiple linear regression. In most cases LC-based LBFs did not perform better in vivo, in terms of a higher area under the curve (AUC0-24 h) and maximal plasma concentration (Cmax), than MC-based LBFs. The administration of supersaturated LBFs resulted in increased AUC0-24 h (1.5 - 3.2-fold) and Cmax (1.1 - 2.6-fold)-values when compared to the non-supersaturated equivalents. Lipase inhibition led to a decreased drug exposure in most cases, especially for LC formulations (AUC0-24 h reduced to 47 - 67%, Cmax to 46 - 62%). The addition of Soluplus® showed a benefit to drug absorption from supersaturated type II LBFs (1.2 - 1.7-fold AUC0-24 h), due to an increased solubility of cinnarizine in the formulation. Upon dose-normalization of the pharmacokinetic parameters, no beneficial effect of Soluplus® could be demonstrated.