Inhibition of growth in young mice treated with d,1-methadone

Neonatal mice were treated with d,1-methadone, 1-alpha-acetylmethadol (LAAM) or the narcotic antagonists, naloxone, nalorphine or levallorphan. Litter mates were injected with normal saline solution and handled in the same way. Treatment began on the second postpartum day and continued daily or on alternate days for up to 6 weeks. Injection of methadone in dosages of 2 mg/kg to mg/kg inhibited weight gain in a log dose-related fashion. LAAM, 1 mg/kg or 2 mg/kg also retarded weight gain. Mice gained weight normally when naloxone, 10 mg/kg was injected with methadone, 2 mg/kg. Furthermore the daily injection of d-methadone, 4 mg/kg, did not inhibit weight gain nor did any of the narcotic antagonists. There findings indicate that growth inhibition induced by methadone is a stereospecific, opioid effect.