The effect of intravenous sulfobutylether7-beta-cyclodextrin on the pharmacokinetics of a series of adamantane-containing compounds

Intravenously administered (i.v.) drug-cyclodextrin (CD) inclusion complexes are generally expected to dissociate rapidly and completely, such that the i.v. pharmacokinetic profile of a drug is unchanged in the presence of CD. The altered pharmacokinetics of a synthetic ozonide in rats has been attributed to an unusually high-binding affinity (2.3 ? 106 M-1) between the drug and sulfobutylether7-?-cyclodextrin (SBE7-?-CD) with further studies suggesting a significant binding contribution from the adamantane ring. This work investigated the binding affinity of three adamantane derivatives [amantadine (AMA), memantine (MEM) and rimantadine (RIM)] to SBE7-?-CD and the impact of complexation on their i.v. pharmacokinetics. In vitro studies defined the plasma protein binding, as well as the impact of SBE7-?-CD on erythrocyte partitioning of each compound. SBE7-?-CD binding constants for the compounds were within the typical range for drug-like molecules (102-104 M-1). The pharmacokinetics of AMA and MEM were unchanged; however, significant alteration of RIM plasma and urinary pharmacokinetics was observed when formulated with CD. In vitro studies suggested two factors contributing to the altered pharmacokinetics: (1) low plasma protein binding of RIM, and (2) decreased erythrocyte partitioning in the presence of high SBE7-?-CD concentrations. This work demonstrated the potential for typical drug-cyclodextrin interactions to alter drug plasma pharmacokinetics.