Determining Population and Developmental Pharmacokinetics of Metronidazole Using Plasma and Dried Blood Spot Samples From Premature Infants


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Abstract

Background:Limited pharmacokinetic (PK) data of metronidazole in premature infants have led to various dosing recommendations. Surrogate efficacy targets for metronidazole are ill-defined and therefore aimed to exceed minimum inhibitory concentration of organisms responsible for intra-abdominal infections.Methods:We evaluated the PK of metronidazole using plasma and dried blood spot samples from infants ≤32 weeks gestational age in an open-label, PK, multicenter (N = 3) study using population PK modeling (NONMEM). Monte Carlo simulations (N = 1000 virtual subjects) were used to evaluate the surrogate efficacy target. Metabolic ratios of parent and metabolite were calculated.Results:Twenty-four premature infants (111 plasma and 51 dried blood spot samples) were enrolled: median (range) gestational age at birth 25 (23–31) weeks, postnatal age 27 (1–82) days, postmenstrual age 31 (24–39) weeks and weight 740 (431–1466) g. Population clearance (L/h/kg) was 0.038 × (postmenstrual age/30)2.45 and volume of distribution (L/kg) of 0.93. PK parameter estimates and precision were similar between plasma and dried blood spot samples. Metabolic ratios correlated with clearance.Conclusion:Simulations suggested the majority of infants in the neonatal intensive care unit (>80%) would meet the surrogate efficacy target using postmenstrual age–based dosing.

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