Journal of pharmacological sciences
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In patients with hypoalbuminemia, the total serum concentration of valproic acid may offer poor clinical information; however, very few clinical laboratories routinely analyze the free concentration of the drug. The aim of this study was to design a procedure to normalize the total concentration of valproic acid according to the level of serum albumin and using previously published free fraction values. In 121 adult patients, with albumin levels of 18 - 41 g/L, the total concentration of valproic acid was normalized using the derived equation: C(N) = alpha(H)C(H)/6.5, where alpha(H) is the free fraction of the drug corresponding to the patient's particular albuminemia and C(H) is the total concentration of valproic acid. ⋯ Furthermore, cases with therapeutic drug concentrations frequently became supratherapeutic when normalized. The limitations and clinical applications of the proposed formula for normalizing the total concentration of valproic acid are presented. It is concluded that it may be useful for the posological management of hypoalbuminemic patients when the free concentration of the drug is not available, and decisions have to be made based on the total serum concentration.