Effect of heterologous combination on competitive nephelometric immunoassay. II. Bridge-heterologous combination for ethosuximide immunoassay.

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Abstract
We developed a competitive nephelometric immunoassay for the determination of ethosuximide. The method was based on the inhibition of immunoprecipitation by a hapten. Each of two ethosuximide derivatives, ethosuximide acetic acid and ethosuximide butyric acid, was conjugated to bovine serum albumin. These conjugates were injected into rabbits to raise anti-ethosuximide antisera. Each derivative was also conjugated to human serum albumin. These two conjugates were allowed to react with the two antisera in combination to form precipitates. Ethosuximide and its derivatives quantitatively inhibited these four precipitation reactions. The results indicated that the anti-(ethosuximide butyrate) antiserum recognized the bridge moiety better than the anti-(ethosuximide acetate) antiserum. Of the four combinations, the heterologous combination of the anti-(ethosuximide butyrate) antiserum with the (ethosuximide acetyl)-human serum albumin conjugate gave the most sensitive immunoassay for ethosuximide.