Characterization of morphine-specific monoclonal antibodies showing minimal cross-reactivity with codeine

Six murine monoclonal antibodies against morphine were produced using N-(4-aminobutyl)normorphine as a hapten. Most of the antibodies obtained distinguished the substituents at the 3 and 6 positions of morphine. This property of the antibodies led to a reduction in cross-reactivity with codeine, morphine-3-glucuronide (M-3-G) and morphine-6-glucuronide (M-6-G) to negligible levels. However, one of the antibodies distinguished the substituent only at the 3 position of morphine, which cross-reacted with M-6-G, naloxone and naltrexone. In the competitive inhibition enzyme-linked immunosorbent assay, morphine was detected at concentrations as low as circa 100 pg/ml.