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Pharmacokinetics of phenytoin in children
Insights
Phenytoin pharmacokinetics, including Vmax and Km, were studied in children and adults. Predicted phenytoin concentrations accurately matched observed levels, indicating reliable pharmacokinetic modeling for both age groups.
Area of Science:
- Pharmacology
- Pediatric Pharmacology
- Clinical Pharmacokinetics
Background:
- Phenytoin is an anticonvulsant medication with variable pharmacokinetics.
- Understanding age-related differences in phenytoin metabolism is crucial for effective dosing.
Purpose of the Study:
- To estimate apparent Vmax and Km for phenytoin in children and adults.
- To validate a pharmacokinetic model for predicting phenytoin concentrations after dose adjustments.
Main Methods:
- Apparent Vmax and Km were determined in 40 children (8-33 months) and 21 adults (18-66 years).
- Observed and predicted steady-state plasma and salivary phenytoin concentrations were compared after dose changes.
Main Results:
- Apparent Km for phenytoin was similar between children (7.5 ± 1.2 mg/l) and adults (9.4 ± 2.3 mg/l).
- Apparent Vmax differed significantly (P < 0.001) between children (20.4 ± 2.1 mg kg-1 day-1) and adults (8.7 ± 0.7 mg kg-1 day-1).
- After correcting for liver weight to body weight ratios, Vmax was similar in both groups, and observed and predicted concentrations showed high correlation (P < 0.001).
Conclusions:
- Phenytoin pharmacokinetics can be reliably modeled in children and adults.
- Age-related differences in Vmax are influenced by body size, and corrected Vmax values are comparable.
- This pharmacokinetic model aids in predicting phenytoin concentrations and optimizing dosing regimens across different age groups.
Abstract:
1 Apparent Vmax and Km for phenytoin were estimated in 40 children (aged 8--33 months) and 21 adults (aged 18--66 years). 2 The derived values of Vmax and Km were used to predict the plasma and salivary concentrations of phenytoin following a change in dose. There was a highly significant correlation between observed and predicted steady-state concentration in both children and adults (P less than 0.001). 3 The apparent Km was similar in children (7.5 +/- 1.2 mg/l) and adults (9.4 +/- 2.3 mg/l). 4 Vmax differed significantly (P less than 0.001) between children (20.4 +/- 2.1 mg kg-1 day-1) and adults (8.7 +/- 0.7 mg kg-1 day-1). 5 After correction for differences in the ratio of liver weight to body weight in children and adults, Vmax was similar in the two groups.