Induction of antibodies to methadone during methadone maintenance treatment of heroin addicts and its possible clinical implications

By means of two different types of enzyme-linked immunosorbent assay (ELISA) techniques, antibodies to methadone were detected in blood plasma of heroin addicts on methadone maintenance treatment. In 11-15% of cases immunoglobulin (Ig) M antibodies were detected, while IgG antibodies were observed in 33-40%. At least two types of antibodies to methadone were induced-antibodies with high affinity to methadone and low-affinity antibodies more specific for morphine than for methadone. The methadone antibody-positive group of patients had a significantly higher plasma methadone concentration--440 ng/ml, than the antibody-negative group--250 ng/ml (P < 0.005) despite almost the same mean therapeutic doses of methadone. Of patients with all types of antibodies to methadone 52% were human immunodeficiency virus (HIV)-positive, whereas in the group without antibodies, HIV-positive reactions were observed in 10.5% only (P < 0.002). Alternatively, 87.5% of HIV-positive patients had antibodies to methadone, a fact which should be taken into consideration during methadone dose adjustment.