British journal of clinical pharmacology
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The glucuronidation of morphine was investigated in 10 premature neonates (postnatal age < 24 h at initiation of treatment) following 24 h of therapy (2 h loading infusion, followed by a constant rate infusion). Morphine, morphine-3-glucuronide (M3G) and morphine-6-glucuronide (M6G) were measured in plasma obtained at 24 h in all babies. Plasma concentrations of M3G and M6G correlated significantly with morphine concentration (P < 0.01 in both cases), and with each other (P < 0.001), suggesting that the capacity for morphine glucuronidation in premature neonates is not saturated at the infusion rates used in this study. ⋯ This probably reflects increase in liver weight with increasing birth weight. Although morphine glucuronidation is deficient in premature neonates, significant concentrations of the respiratory stimulant M3G are achieved rapidly (20% of morphine plasma concentrations at 2 h). At this time, the respiratory depressant M6G could not be detected.