Stereospecificity of antibody: quinine, the optical isomer of quinidine and anti-malarial drug chloroquine do not cross-react with quinidine immunoassays.

Abstract

Quinine is an optical isomer of quinidine. Both quinine and chloroquine (an aminoquinoline derivative) are used in treating malaria. The authors studied cross-reactivity of quinine and chloroquine with the quinidine immunoassays using the TDx and AxSYM analyzers (Abbott Laboratories, Abbott Park, IL). The authors observed no cross-reactivity of chloroquine with quinidine immunoassays (TDx and AXSYM) even when drug-free serum was supplemented with 1000 microg/mL chloriquine. The authors observed no cross-reactivity of quinine up to a concentration of 250 microg/mL. At higher concentrations, the authors observed a small cross-reactivity. The cross-reactivity of a substance should be studied in the presence of the primary analyte. When serum pools prepared from patients receiving quinidine were supplemented with various concentrations of quinine or chloroquine, the authors observed statistically significant declines in quinidine concentrations with higher concentrations of both quinine and chloroquine. The authors observed significant cross-reactivity of L-amphetamine with the amphetamine immunoassay also marketed by Abbott Laboratories and run on the AxSYM analyzer. The authors conclude that although the antibody used in the quinidine assay is stereospecific, the antibody used in the amphetamine assay by the same manufacturer is not stereospecific.