Introduction Morphine has been used for relief of labour pain since the early twentieth century . After World War II the synthetic opioid meperidine, which was believed to cause less neonatal depression than morphine  came into use and morphine fell into disrepute as an obstetric analgesic. While the kinetics of morphine in human pregnancy have apparently never been studied, several investigations have been performed on the disposition of meperidine [15, 26, 31] and other new obstetric analgesics such as meptazinol  in the pregnant woman and in the neonate. It has been demonstrated that meperidine is slowly eliminated from the neonate [5, 7, 15] and the presence of the drug for several days in the neonatal urine indicates a potential for pharmacological effects during that period . This drawback of meperidine as an obstetric analgesic agent was the basis of our renewed interest in morphine as a reliever of labour pain. Furthermore, in investigations on systemic analgesia during labour, morphine remains the standard with which other analgesics are compared . Morphine is primarily eliminated by conjugation in the liver. Morphine-3-glucuronide (M3G), its major metabolite, lacks an analgesic effect  and is highly water soluble and excreted via
Journal of Perinatal Medicine – de Gruyter
Published: Jan 1, 1990
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