Albumin-Normalised Valproate Concentration Calculator

Overview

Estimates a normalised total valproate concentration using the Hermida–Tutor albumin-based free-fraction model.

Clinical Significance

The result is a theoretical normalisation, not a measured free valproate concentration. Direct free-level measurement is preferred when protein binding is markedly abnormal.

When to Use

• Use when the required concentration, timing and dosing information are reliable and the stated pharmacokinetic assumptions are reasonable.
• Use within an approved therapeutic-drug-monitoring or medicines-governance pathway.
• Use to support transparent review, not to automate prescribing.

How It Is Calculated

• CN = αH × CH ÷ 0.065, where αH is an albumin-derived free fraction; MedicalC estimates αH from the published model.
• MedicalC validates that all required inputs are numeric and rejects internally impossible time or concentration relationships where applicable.

Interpretation

• The result is a theoretical normalisation, not a measured free valproate concentration. Direct free-level measurement is preferred when protein binding is markedly abnormal.
• Interpret the result with the clinical indication, microbiology or seizure control, organ function, assay timing and local targets.

Worked Example

Enter a verified set of source values in the displayed units. MedicalC applies: CN = αH × CH ÷ 0.065, where αH is an albumin-derived free fraction; MedicalC estimates αH from the published model. Recheck the source chart and sampling times before using the result.

Patient Considerations

• The original model was derived in adults with hypoalbuminaemia and may perform poorly in critical illness, pregnancy, renal failure, very high concentrations or displacement interactions.
• Consider acute kidney injury, augmented renal clearance, fluid shifts, obesity, burns, pregnancy, critical illness and interacting medicines.

Limitations

• One-compartment equations may not describe distribution or multicompartment behaviour accurately.
• Derived values can appear precise despite uncertainty in sampling time, assay result and clearance stability.
• A calculated exposure or dose does not establish clinical benefit or safety.

Clinical Pearls

• Critical illness can alter valproate binding through mechanisms not captured by albumin alone, so even a mathematically corrected value may be misleading.
• Plot concentrations against actual elapsed time before accepting any pharmacokinetic slope.
• When the result conflicts with the patient, verify the data rather than forcing a dose change.

Common Mistakes

• Using scheduled rather than actual administration and blood-sampling times.
• Treating a level drawn during distribution as a post-distribution concentration.
• Mixing mg/L, micrograms/mL and micrograms/L.
• Applying steady-state equations before steady state or during changing clearance.
• Using a generic concentration target outside the relevant indication or local protocol.

Evidence Base

Principal source: Hermida J, Tutor JC. A theoretical method for normalizing total serum valproic acid concentration in hypoalbuminemic patients. J Pharmacol Sci. 2005.

References

1. Hermida J, Tutor JC. A theoretical method for normalizing total serum valproic acid concentration in hypoalbuminemic patients. J Pharmacol Sci. 2005. — Primary publication, consensus guideline or authoritative pharmacokinetic source.