Valproic Acid Oral Solution Dosing Equivalence
5 mL of the oral valproic acid solution (250 mg/5 mL) is equivalent to one 250 mg tablet.
Direct Calculation
The concentration of the oral solution is 250 mg per 5 mL, which means:
- 250 mg ÷ 5 mL = 50 mg/mL
- To deliver 250 mg: 250 mg ÷ 50 mg/mL = 5 mL
Bioavailability Considerations
- Valproic acid oral formulations (solutions, tablets, enteric-coated capsules) have bioavailability approaching 100%, making them therapeutically equivalent on a milligram-per-milligram basis 1
- The primary difference between formulations is the absorption half-life, which varies from less than 30 minutes for solutions to 3-4 hours for enteric-coated preparations, but this does not affect total drug delivery 1
Clinical Context
- Once absorbed, valproic acid has a relatively small volume of distribution (0.1-0.4 L/kg) and is largely bound to plasma proteins, with therapeutic plasma concentrations typically ranging from 50-100 mg/L 1, 2
- The half-life in adults varies from 10-20 hours, while it is significantly shorter (6-9 hours) in children, which affects dosing frequency but not individual dose equivalence 1
Important Formulation Note
- Do not assume that two 250 mg tablets equal one 500 mg tablet for combination products (such as amoxicillin-clavulanic acid formulations where clavulanic acid content differs), though this caveat does not apply to single-ingredient valproic acid products 3