Different pharmacokinetics of tramadol in mothers treated for labour pain and in their neonates

Contains fulltext : 49100.pdf (Publisher’s version ) (Closed access) OBJECTIVE: The aim of the present study was to investigate the pharmacokinetic profile of tramadol hydrochloride in neonates, born from mothers who underwent analgesia with tramadol for the relief of labour pain.METHODS: Intramuscular tramadol (100--250 mg) was administered to 22 mothers giving birth who requested pain relief. At the time of birth (1.5--6.0 h after last tramadol dose), maternal and umbilical blood samples were taken. Another venous blood sample was drawn from each neonate, and at the same time from its mother, at 1, 2, 3, 6 or 12 h post-partum, providing the data for a population pharmacokinetic evaluation of tramadol and its metabolite M1. Routine APGAR scores and a standard neurological and adaptive capacity test were considered for evaluation of the effect of tramadol on the neonates.RESULTS: Serum tramadol concentrations at the time of birth (t(0)) were 243+/-102 ng/ml (mean+/-SD, umbilical vein), 258+/-103 ng/ml (umbilical artery) and 250+/-113 ng/ml (maternal vein). Serum M1 concentrations were 52+/-27 ng/ml (umbilical vein), 47+/-24 ng/ml (umbilical artery) and 56+/-21 ng/ml (maternal vein). The two-compartment type elimination profiles during the first 12 h post-partum for neonates (and mothers, respectively) were characterised by terminal t(1/2) (tramadol)=7.0 (7.2) h and t(1/2) (metabolite M1)=85.0 (5.5) h.CONCLUSION: The intramuscular application of tramadol in birth-giving mothers almost freely reaches the neonate, confirming a high degree of placental permeability. The neonates already possess the complete hepatic capacity for the metabolism of tramadol into its active metabolite. However, the renal elimination of the active tramadol metabolite M1 is delayed, in line with the slow maturation process of renal function in neonates. Despite this difference in pharmacokinetics between neonates and adults, the intramuscular application of tramadol at the recommended dosage range during delivery appears to effective in the relief of labour pain.