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Plasma levels of oxybutynine chloride in children
E Autret1, A P Jonville, J P Dutertre
1Department of Clinical Pharmacology, University Hospital of Tours, France.
Insights
Plasma oxybutynine levels in children treated for incontinence were measured. Doses adapted to body weight showed concentrations similar to adults, suggesting current regimens may be inappropriate and weight-based dosing is preferred.
Area of Science:
- Pharmacology
- Pediatrics
- Clinical Chemistry
Background:
- Anticholinergic adverse effects of oxybutynin in children prompted investigation.
- Conventional dosing regimens in pediatric patients required evaluation.
Purpose of the Study:
- To measure plasma oxybutynin levels in children treated for daytime incontinence.
- To compare pediatric plasma concentrations with adult levels at equivalent doses.
- To assess the suitability of current dosing regimens and explore weight-based dosing.
Main Methods:
- Plasma oxybutynin concentrations were measured in 18 children (aged 5-13 years) on day five of treatment.
- Dosing was adapted to body weight (0.1 mg/kg for 5-8 years, 0.15 mg/kg for 10-13 years), administered twice daily at 12-hour intervals.
- Concentrations were measured at intervals post-administration to determine pharmacokinetic profiles.
Main Results:
- Peak plasma oxybutynin concentrations typically occurred 1-2 hours after administration.
- Oxybutynin was rapidly cleared, with levels becoming unmeasurable in 14 of 18 children after 6 hours.
- Measured plasma concentrations in children were comparable to those in adults receiving equivalent weight-adjusted doses.
Conclusions:
- Weight-adjusted dosing of oxybutynin in children yields plasma concentrations similar to adults.
- The study did not identify specific pediatric pharmacokinetic differences to explain adverse effects.
- Results support a weight-based dosage regimen with 12-hour intervals, questioning previously proposed regimens.
Abstract:
Anticholinergic adverse-effects in children treated with conventional doses of oxybutynine led us to measure plasma oxybutynine levels in children. 18 children, aged 5 to 13 y, who required treatment with oxybutynine chloride for daytime incontinence were studied. Plasma concentrations were measured on the fifth day of a course of treatment in which the dose was adapted to the child's body weight; the dose was given twice daily at 12-hour intervals. In 10 children aged between 5 and 8 y, the mean dose was 0.1 mg.kg-1. In 8 children aged between 10 and 13 years, the mean dose was 0.15 mg.kg-1. The highest concentration was usually found between 1 and 2 h after administration. The subsequent fall in concentration was rapid and after 6 h oxybutynine was no longer measurable in 14 of the children. The concentrations found were not different from those seen in adults given equivalent doses. The results show that plasma concentrations in children were not very different from those observed in adults if the dose were adapted to the body weight of the children. No special differences in paediatric use were revealed that might explain the particular adverse-effects. The results of the study argue against the dosage regimen proposed before these adverse events were detected. They strongly favour a dose adapted to the body weight of the child, with a 12-hour interval between doses.