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Interaction between valproic acid and aspirin in epileptic children: serum protein binding and metabolic effects
Insights
Aspirin increased valproic acid (VPA) levels in epileptic children by displacing it from albumin and altering its metabolism. This interaction necessitates careful monitoring of VPA dosage when co-administered with aspirin.
Area of Science:
- Pharmacology
- Clinical Pharmacy
- Pediatric Neurology
Background:
- Valproic acid (VPA) is a widely used antiepileptic drug.
- Understanding drug interactions is crucial for optimizing VPA therapy, especially in children.
Purpose of the Study:
- To investigate the effect of aspirin on the pharmacokinetics of valproic acid in epileptic children.
- To determine if aspirin alters VPA serum protein binding and elimination.
Main Methods:
- Assessed serum VPA concentrations (total and free fractions) and half-life in six epileptic children before and during co-administration of aspirin.
- Evaluated in vitro and in vivo albumin binding constants for VPA in the presence of salicylate.
- Monitored renal excretion of VPA and its metabolites.
Main Results:
- Serum free VPA fractions increased significantly (12% to 43%) in five of six children taking VPA with aspirin.
- Mean VPA half-life increased, and both total and free VPA trough concentrations were higher with co-administration.
- Salicylate decreased in vitro VPA-albumin binding, suggesting in vivo displacement, and altered VPA elimination patterns.
Conclusions:
- Aspirin significantly increases serum VPA levels in children, primarily by displacing VPA from albumin.
- The interaction also involves alterations in VPA metabolism and renal excretion, leading to a longer VPA half-life.
- Clinical monitoring of VPA levels is recommended when co-administered with aspirin in pediatric epilepsy patients.
Abstract:
In five of six epileptic children who were taking 18 to 49 mg/kg/day valproic acid (VPA), the steady-state serum free fractions of VPA rose from 12% to 43% when antipyretic doses of aspirin were also taken. Mean total VPA half-life (t1/2) rose from 10.4 +/- 2.7 to 12.9 +/- 1.8 hr and mean free VPA t1/2 rose from 6.7 +/- to 2.1 to 8.9 +2- 3.0 hr when salicylate was present in the serum. The in vitro albumin binding association constant (ka) for VPA was decreased by salicylate, but the in vivo ka value was not affected. The 12-hr (trough) concentrations of both free and total VPA were higher in the presence of serum salicylate in five of six patients. Renal excretion of unchanged VPA decreased in five of six patients, but the VPA carboxyl conjugate metabolite-excretion patterns were not consistently affected. Salicylate appeared to displace VPA from serum albumin in vivo, but the increased VPA t1/2 and changes in VPA elimination patterns suggest that serum salicylate also altered VPA metabolism.