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Clonazepam serum protein binding during development
Insights
Clonazepam exhibits lower protein binding in umbilical cord serum compared to adults. This difference in binding capacity and affinity normalizes within the first year of life in children.
Area of Science:
- Pharmacology
- Clinical Chemistry
Background:
- Understanding drug pharmacokinetics is crucial for safe and effective therapeutic use, especially in pediatric populations.
- Clonazepam, a benzodiazepine, is widely prescribed, necessitating a clear understanding of its protein binding characteristics across different age groups.
Purpose of the Study:
- To investigate the differences in clonazepam protein binding in umbilical cord serum, children, and adults.
- To characterize the kinetics of clonazepam serum protein binding, including binding capacity and affinity, in neonates and adults.
Main Methods:
- Protein binding of clonazepam was assessed in serum samples from umbilical cords, children (2 months to 12 years), and adults (27 to 40 years).
- Kinetic parameters, including the number of binding sites (n) and association constant (K), were determined using double reciprocal plots.
Main Results:
- The unbound fraction of clonazepam was significantly higher in umbilical cord serum (17.3%) than in adult serum (13.9%).
- In children, unbound clonazepam levels reached adult values within the first year of life.
- Adult serum demonstrated lower binding capacity (n) but higher affinity (K) for clonazepam compared to umbilical cord serum.
Conclusions:
- Neonatal serum exhibits reduced binding capacity and affinity for clonazepam compared to adult serum.
- The pharmacokinetic profile of clonazepam in children matures rapidly, reaching adult levels of protein binding within the first year of life.
Abstract:
Clonazepam protein binding was investigated in sera from five different umbilical cords, 45 children (aged 2 mo to 12 yr), and five adults (aged 27 to 40 yr). The unbound fraction (means +/- SE) of clonazepam was 17.3% +/- 0.7% in umbilical cord serum and 13.9% +/- 0.2% in adult serum (P less than 0.01). In children, the unbound fraction of clonazepam reached the adult values during the first year of life. The kinetics of clonazepam serum protein binding were studied in three umbilical cord serum and three adult serum specimens. The number of binding sites (n, reported as moles per gram protein) and the association constant (K, reported as M-1) were estimated from double reciprocal plots of 1/r against 1/D (r is the number of moles bound per gram plasma protein; D is the molar concentration of unbound drug). In umbilical cord sera, the mean values (+/- SE) of n and K were 8.4 +/- 0.6 X 10(-7) mol/gm and 8.3 +/- 0.9 X 10(4) M-1. In adult serum samples the corresponding values were 3.0 +/- 0.8 X 10(-7) mol/gm and 2.7 +/- 0.6 X 10(5) M-1, which indicated lower binding capacity but higher affinity for clonazepam of plasma proteins in adults than in children.