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Phenobarbital doses necessary to achieve 'therapeutic' concentrations in children
1Division of Clinical Pharmacology/Toxicology, Children's Hospital, Columbus, Ohio.
Insights
Phenobarbital (PB) dosing in children requires careful consideration of age. Plasma concentrations of PB vary significantly with age, necessitating higher doses in children under 11 to reach therapeutic levels.
Area of Science:
- Pharmacology
- Clinical Pharmacy
- Pediatric Neurology
Background:
- Phenobarbital (PB) is a widely used antiepileptic drug.
- Accurate dosing is crucial for therapeutic efficacy and minimizing toxicity.
- Understanding age-related pharmacokinetic variations is essential for optimizing PB therapy, particularly in pediatric populations.
Purpose of the Study:
- To investigate the relationship between age, drug formulation, concomitant medications, and steady-state plasma phenobarbital concentrations.
- To determine optimal phenobarbital dosing strategies in pediatric patients based on age-related pharmacokinetic profiles.
Main Methods:
- Analysis of steady-state plasma phenobarbital concentrations (n=671) from 438 inpatients.
- Evaluation of the influence of age, sex, drug formulation (tablet, elixir, intravenous), and combination therapy on the phenobarbital dose ratio (concentration/dose).
Main Results:
- A significant relationship was observed between age and the PB dose ratio, with dose ratios declining in infants under one year and increasing after age one.
- Patients on combination antiepileptic drug therapy exhibited significantly higher PB dose ratios.
- Neither sex nor the formulation of PB administered affected the dose ratio.
Conclusions:
- Pediatric patients, particularly those under 11 years, may require phenobarbital maintenance doses exceeding 5 mg/kg/day to achieve therapeutic concentrations (10-40 mg/l).
- Age-specific dosing adjustments are critical for effective phenobarbital therapy in children.
- Concomitant antiepileptic drug use necessitates careful monitoring of phenobarbital levels.
Abstract:
Steady-state plasma phenobarbital (PB) concentrations (n = 671) were measured in 438 inpatients. There was a significant relationship between age and PB dose ratio (concentration/dose or 1/clearance) for monotherapy patients; the dose ratio declined in the first year of life, but the dose ratio increased after age 1. The dose ratios were significantly higher in patients receiving PB in combination with other antiepileptic drugs. However, neither sex nor formulations used (tablet, elixir and intravenous) had any influence on the PB dose ratio. The age-dose-concentration relationships indicate that children, especially those under 11 years of age, may require maintenance PB doses more than 5 mg/kg/day to achieve the commonly recommended 'therapeutic' concentration range (10-40 mg/l).