Specific antibodies to theophylline for use in a homogeneous enzyme immunoassay.

Bovine serum albumin conjugate of 1-methyl-3-(3'-carboxypropyl)xanthine elicits highly specific anti-theophylline antibodies when injected into sheep. When used in a homogeneous enzyme immunoassay for theophylline these antibodies show insignificant cross-reactivity (less than 1%) to 1-methyl- and 1,3-dimethyluric acid, 3-methylxanthine, caffeine, and theobromine. In contrast, immunogens prepared from the C-8 functionalized drug afford antibodies which show more serious cross-reactivity to these compounds. Plausible rationale for attachment of the drug to carrier proteins through its N-3 position which furnished specific antibodies are given.