Free Valproic Acid Concentrations Research Articles

Determination of Free Valproic Acid Concentration in 569 Clinical Samples by LC-MS/MS After Hollow Fiber Centrifugal Ultrafiltration Treatment.

To perform therapeutic drug monitoring of total and free plasma valproic acid (VPA) concentrations in clinical samples and to analyze the related factors. The total VPA concentration in plasma was determined by ultrahigh-performance liquid chromatography with precolumn derivatization with α-bromoacetophenone, and the free VPA concentration was determined by liquid chromatography-tandem mass spectrometry after the plasma was treated by hollow fiber centrifugal ultrafiltration. Regression analysis was performed to examine the associations between free plasma VPA, total plasma VPA, and the plasma protein binding rate. The impact of individual situations, outpatient or inpatient factors, and drug combinations on VPA concentrations were examined. Of the 569 clinical samples, 268 were inpatients and 301 were outpatients, and the total VPA concentration in 138 cases (24.2%) was lower than the effective treatment concentration range; the total and free VPA concentrations in outpatient samples were 11.0% and 26.1% higher than those of inpatients, respectively. There was no linear relationship between the free and total VPA concentrations. The relationship equation between the plasma protein binding rate and free VPA concentrations was as follows: Y = 0.0255X2 - 1.1357X + 97.429 (r = 0.8011). The total and free VPA concentrations were significantly decreased after the coadministration of phenobarbital (83.7% and 64.3% of the control group, P < 0.05) or carbapenem antibiotics (32.0% and 32.7% of the control group, P < 0.05). The total VPA concentrations in patients with epilepsy at our hospital was lower than the effective treatment concentration range, which was inadequate for epilepsy control; the total VPA concentrations of outpatients were higher than those of inpatients; as phenobarbital affects VPA metabolism, therapeutic drug monitoring is recommended. Carbapenem antibiotic coadministration with VPA should be avoided because carbapenem antibiotics can lead to the failure of VPA antiepileptic treatment.

CYP2C9*3/*3 Gene Expression Affects the Total and Free Concentrations of Valproic Acid in Pediatric Patients with Epilepsy.

PurposeTo perform therapeutic drug monitoring (TDM) of total and free plasma valproic acid (VPA) concentrations in pediatric patients with epilepsy and to analyze related factors.Patients and MethodsPediatric epileptic patients treated in 2015–2019 in our hospital were assessed. Total and free plasma VPA concentrations were obtained by UPLC and LC-MS/MS, respectively. Regression analysis was performed to examine the associations of free plasma VPA with total plasma VPA and plasma protein binding rate. The impacts of individual situation, CYP2C9 genotype, and drug combination on VPA concentration were examined.ResultsOf the 251 patients, 81 had lower total concentrations than effective therapeutic levels; 86 and 31 patients had infections and central nervous system dysplasia, respectively. VPA’s daily doses and free drug concentrations were significantly lower in the CYP2C9 *3/*3 genotype group versus the CYP2C9 *1/*3 and CYP2C9 *1/*1 groups (P<0.05). Free and total VPA concentrations were linked by Y = 0.0004 X2 + 0.042 X + 0.3035 (r=0.6981); VPA plasma protein binding rate and free VPA concentration were related by Y = 0.0003 X2 - 0.0127 X + 0.9777 (r=0.8136). Both total and free VPA concentrations were significantly decreased in patients simultaneously administered phenobarbital, meropenem and biapenem (P<0.05), with therapeutic failure after meropenem/biapenem co-administration.ConclusionFree VPA amounts have nonlinear relationships with total VPA amounts and plasma protein binding rate in epileptic children. Additionally, CYP2C9 *3/*3 expression affects VPA metabolism. Since phenobarbital affects VPA metabolism, TDM is recommended. Meanwhile, carbapenem-co-administration with VPA should be prohibited.

Factors to influence the accuracy of albumin adjusted free valproic acid concentration

Therapeutic drug monitoring (TDM) is recommended during treatment with valproic acid (VPA), as is the measurement of free VPA concentration (MfVPA). However, MfVPA is unavailable in many institutions. Based on the highly protein-bound characteristics of VPA, an albumin-adjusted formula has been proposed to predict free VPA concentration (PfVPA). Nevertheless, the factors affecting the accuracy of this formula remain unknown, as does the concordance between MfVPA and PfVPA. Adult patients receiving VPA and undergoing TDM were enrolled. Free and total serum concentration (TVPA) were categorized as subtherapeutic, therapeutic, or supratherapeutic based on the reference range of 5-15 and 50-100μg/mL, respectively. Concordance was defined as MfVPA and PfVPA, or MfVPA and TVPA, falling within the same category. Multivariate logistic regression with generalized estimating equation was adopted to identify factors affecting concordance, and the receiver operating characteristic curve was applied to determine the cutoff values of predictors. A total of 98 data points from 51 participants were included for analysis. The concordance of MfVPA and PfVPA, and MfVPA and TVPA, was 72% and 44%, respectively. Blood urea nitrogen (BUN) (0.97 [0.95-0.99], P=0.01) and TVPA (0.97 [0.95-0.99], P=0.02) had a significant influence on the concordance of MfVPA and PfVPA. The cutoff values of TVPA and BUN for the accuracy of the albumin-adjusted formula were 56.4μg/mL and 51.05mg/dL, respectively. If MfVPA is not available, the albumin-adjusted formula should be applied before VPA dosage adjustment when TVPA is<56.4μg/mL and BUN is<51.05mg/dL.

Safety range of free valproic acid serum concentration in adult patients

BackgroundTherapeutic drug monitoring (TDM) is recommended during valproic acid (VPA) use, and total serum concentration has been widely adopted. However, the free form of VPA is responsible for its pharmacologic and toxic effects, and the total and free concentrations are highly discordant because of VPA’s highly protein bound and saturable binding characteristics. Therefore, free VPA monitoring is increasingly advocated. Nevertheless, the correlation between free VPA concentration and associated adverse effects remains unknown.ObjectiveTo determine the optimal safety range of free VPA concentration in adult patients.Materials and methodsThis prospective cohort study enrolled adult patients undergoing VPA therapy with TDM. Patient characteristics, VPA use, and adverse effects (thrombocytopenia, hyperammonemia, and hepatotoxicity) were recorded. A multivariate logistic regression model was applied to identify the predictors of adverse effects, and the receiver operating characteristic curve was applied to locate the cutoff point of free VPA concentration.ResultsA total of 98 free serum concentrations from 51 patients were included for final analysis. In total, 31 (31.6%), 27 (27.6%), and 4 (4.1%) episodes of hyperammonemia, thrombocytopenia, and hepatotoxicity were observed, respectively. Free VPA concentration was a predicting factor for thrombocytopenia but not for hyperammonemia. A free VPA concentration of >14.67 mcg/mL had the greatest discriminating power (area under the curve = 0.77) for the occurrence of thrombocytopenia.ConclusionsA free VPA serum concentration of 14.67 mcg/mL had the optimal discriminating power for the occurrence of thrombocytopenia. Ammonemia should be monitored even if free VPA concentration is within the safety range.

Abstract 272: Dose Optimization of Early High-Dose Valproic Acid for Neuroprotection After Cardiac Arrest

Introduction: High-dose valproic acid (VPA) has been shown to improve the survival and neurologic outcomes in preclinical brain injury models including asphyxial cardiac arrest (CA) in rats. However, its pharmacokinetics, pharmacodynamics, and safety profiles in large animal CA models are unknown. Hypothesis: High-dose VPA can be safely administered after return of spontaneous circulation (ROSC) and cross the blood-brain barrier dose-dependently in a swine CA model. Methods: After 8 minutes of untreated ventricular fibrillation CA, male Yorkshire swine [43.3 (3.0) kg] were resuscitated for up to 16 minutes until ROSC. They were randomized to receive placebo, 75 mg/kg, 150 mg/kg, or 300 mg/kg VPA as 90-minute intravenous infusion (n=5 per group) beginning 20 minutes after sustained ROSC. Animals were monitored for 2 additional hours after infusion ended and then euthanized. Experimental operators were blinded to the treatments. Results: The mean total cardiac arrest duration was 15.0 (1.6) minutes, with no significant differences between groups. At end of infusion, the serum free VPA concentration increased dose dependently, from 139.2 (10.1) mcg/mL [75 mg/kg VPA] to 287.2 (24.6) mcg/mL [150 mg/kg VPA] to 565.6 (36.5) mcg/mL [300 mg/kg VPA] (p&lt;0.05). This corresponded to a dose-dependent decrease in the fraction of serum protein-bound VPA, from 41.8% (1.8) [75 mg/kg VPA] to 23.4% (3.8) [150 mg/kg VPA] to 14.4% (3.8) [300 mg/kg VPA] (p&lt;0.05). Brain total VPA concentrations at end of experiment were 26.1 (3.1) mcg/g [75 mg/kg VPA], 72.5 (18.9) mcg/g [150 mg/kg VPA], and 212.3 (33.4) mcg/g [300 mg/kg VPA] (p&lt;0.05). There was a strong linear correlation between serum free VPA and brain total VPA concentrations (R 2 =0.98). All animals survived until euthanasia, although the 300 mg/kg group required more epinephrine to maintain mean arterial pressure greater than or equal to 80 mmHg and had higher lactic acidosis. Conclusion: Brain VPA concentrations correlate strongly with serum free VPA when high-dose intravenous VPA is given after ROSC in a swine CA model. These results provide the foundation for dose-optimization studies of high-dose VPA as a neuroprotective therapy following resuscitation from CA.

Accuracy of Valproic Acid Concentration Correction Based on Serum Albumin.

Patient-specific factors can alter the pharmacokinetic disposition of valproic acid. Specifically, the free fraction of valproic acid can increase substantially in patients with hypoalbuminemia or as serum drug concentrations rise due to saturable protein binding. Direct measurement of free serum drug concentrations allows for accurate assessment of drug levels, but the assay may not be readily available in all institutions. The effect of hypoalbuminemia on free fraction has been quantified and serves as the basis of an equation used to "correct" measured total valproic acid concentrations. The aim of this study was to evaluate the accuracy of the equation. This retrospective study included adult patients with measurable free and total valproic acid concentrations between July 2014 and June 2017. The primary aim was to assess the relationship between measured and predicted free valproic acid concentrations. Free levels were categorized as subtherapeutic, therapeutic, or supratherapeutic based on the reference range of 7-23mg/L. Concordance was defined as measured and predicted concentrations falling within the same category. The analysis included 174 patients with a median age of 58years and a median albumin of 3g/dL. The majority of patients were hospitalized (88.5%). Concordance occurred in 56.9% of samples. A Spearman's correlation coefficient of 0.60 (p < 0.001) was found between the measured and predicted free valproic acid concentrations. Concordance of concentrations was 42% for ICU patients, 63% for floor patients, and 65% for outpatients. Of those with discordant concentrations, 97% of the predicted concentrations underestimated the measured concentrations. There is discordance between predicted and measured free serum valproic acid concentrations when using the proposed equation. Because of the potential impact of underestimation and variability of free valproic acid concentrations, a measured free level is the ideal option for therapeutic drug monitoring of valproic acid.

Valproate serum concentrations in patients with hypoalbuminemia and medical complications.

Valproic acid (VPA) and its derivatives are highly protein bound with free fraction increasing with dose and serum concentration. Consensus guidelines regarding dose adjustment for hypoalbuminemia are not available. A literature search was performed using PubMed to identify articles with the following key terms: "valproate," "valproic acid," "protein binding," "albumin," and "hypoalbuminemia." We report our findings as well as 5 cases involving pharmacokinetic impact of hypoalbuminemia on valproate. A previously published model for normalizing VPA serum concentration for hypoalbuminemia in patients with epilepsy was compared to results for 5 cases (4 female, 1 male) in which VPA was used for psychiatric illness. Only 1 of the cases had free serum concentrations in the range that would be expected with the model. Free concentrations ranged from 22% to 83% with no clear relationship to other factors (weight, age, serum creatinine, or dose). Female patients with similar albumin had higher free fractions than the 1 male patient. Due to the variability in pharmacokinetic impact of hypoalbuminemia, it is important to monitor patients closely for signs of VPA toxicity in cases involving altered albumin levels. It would be prudent to use free serum VPA concentrations when patients experience fluctuations in albumin or have unexpected response to medication.

Correlation of saliva and serum free valproic acid concentrations in persons with epilepsy

PurposeTherapeutic drug monitoring (TDM) of antiepileptic drugs (AEDs) in serum is frequently used in clinical settings however saliva could be an alternative to measure free concentration of drugs. In the present study, we observed the possible correlation of VPA concentration between serum and saliva in persons with epilepsy (PWE). MethodsA total of 59 paired serum and saliva samples were assayed from 65 consecutive PWE (51 males and 14 females; age range 9–65 years). Patients were subjected to either VPA monotherapy or its combination with other AEDs for at least three months. Steady state trough concentration of unbound VPA drug was quantified using HPLC. The correlation between serum and saliva free VPA concentration was evaluated. ResultsOut of 65 patients, 27 were on monotherapy of VPA and 38 were on VPA with other antiepileptic drugs. Saliva VPA concentration significantly correlated with serum free VPA concentration (p<0.05). Poor correlation was observed between serum and saliva VPA concentration with the daily dose (p>0.05) respectively. ConclusionsOur study reveals that serum and saliva VPA concentrations are significantly associated in PWE. These associations may facilitate monitoring and evaluation of VPA levels non-invasively for PWE.

DETERMINATION OF TOTAL AND UNBOUND CONCENTRATIONS OF VALPROIC ACID IN HUMAN PLASMA BY LIQUID CHROMATOGRAPHY-TANDEM MASS SPECTROMETRY

An analytical method for the determination of valproic acid in human plasma and ultrafiltrated human plasma has been developed and validated. The analytical method lies in the solid phase extraction of valproic acid (VPA), followed by its quantification through an LC-MS method, using benzoic acid as the internal standard. The intra-assay and inter-assay precisions of this technique ranged between 4.29% and 9.91% and its accuracy ranged between 1.00% and 7.73%, for VPA spiked in plasma matrix. For VPA spiked in ultrafiltrated plasma, matrix precisions were from 6.29% to 9.84% and accuracies, from −1.17% to 5.38%. The limit of quantification was set at 1 µg/mL (precision 3.20%, accuracy 11.31%). The linear working range of concentrations was established between 10 and 250 µg/mL for the plasma matrix and between 1 and 100 µg/mL for the ultrafiltrated plasma matrix. The absolute recovery of valproic acid was over 82% in the studied range of concentrations in both matrixes. Valproic acid was found to be stable in both matrixes at the assayed conditions. This method has shown to be suitable for the analysis of free and total valproic acid concentrations in human plasma samples.

Correlation between Plasma Ammonia Level and Serum Trough Concentration of Free Valproic Acid in Patients with Epilepsy

Therapeutic drug monitoring of valproic acid (VPA) is essential to prevent toxicity, but the correlation between plasma ammonia level and serum VPA concentration remains unclear. We examined the correlation of plasma ammonia level with VPA dose and serum trough concentrations of total and free VPA in Japanese patients with epilepsy. Thirty-eight data sets from 19 Japanese patients with epilepsy were analyzed. The relations of VPA dose and serum total and free VPA concentrations with plasma ammonia level, and the breakpoints of VPA parameters predicting hyperammonemia (plasma ammonia higher than 60 µmol/L) were analyzed. A significant positive correlation was observed between plasma ammonia level and VPA dose (r(s)=0.56, p=0.00062), serum trough total VPA concentration (r(s)=0.55, p=0.00086) and serum trough free VPA concentration (r(s)=0.58, p=0.00041). The breakpoints predicting hyperammonemia were VPA dose of 30.4 mg/kg, serum trough total VPA concentration of 90.9 µg/mL, and serum trough free VPA concentration of 8.65 µg/mL, with impurity reductions at 1.35, 1.35 and 2.02, respectively. These findings suggest that serum trough concentration of free VPA is the most reliable predictor for hyperammonemia, and that the risk of developing hyperammonemia may increase in patients with serum trough free VPA concentrations higher than 8.65 µg/mL.

The Diurnal Fluctuations in Free and Total Serum Valproic Acid Concentration at Steady State in Epileptic Children

The Diurnal Fluctuations in Free and Total Serum Valproic Acid Concentration at Steady State in Epileptic Children

The Impact of Dosage of Sustained-Release Formulation on Valproate Clearance and Plasma Concentration in Psychiatric Patients

Pharmacokinetic parameters were compared between 2 dosages of valproic acid (VPA) sustained-release (SR) formulation in psychiatric patients. A total of 66 psychiatric patients (21 women and 45 men; age range, 18-60 years) receiving 500 mg/d (n = 28) or 1000 mg/d (n = 38) of VPA SR for at least 4 weeks were recruited into the study. A 5-mL blood sample was collected into a plain tube and immediately centrifuged for plasma. Separation of free VPA was further done using Centrifree micropartition devices. Both total and free VPA concentrations (C(total) and C(free)) were analyzed by TDx analyzer with fluorescence polarization immunoassay technique. The patients' characteristics and pharmacokinetic parameters were compared between the 2 dosage groups using independent t test or χ² test where appropriate. The results show that the increment in C(total) (mg/mL) for every milligram-per-kilogram increment in dosage was decreased from 7 ± 3 to 4 ± 1 (mg/L) / (mg/kg) when the total VPA clearance (CL(total)) increased from 6.1 ± 2.6 to 9.0 ± 3.1 mL/kg per hour with the increasing dose in the 500 mg/d and 1000 mg/d groups, respectively (P < 0.05). The increment in C(free) [0.6 ± 0.3 vs 0.5 ± 0.2 (mg/L) / (mg/kg)] and CL(free) (80.4 ± 41.5 vs 92.2 ± 47.6 ml/kg per hour) were not significantly different. Owing to the saturation of protein binding, percent free VPA was significantly increased from 8 ± 3 to 11 ± 3 when the dose was increased from 500 to 1000 mg/d (P < 0.05). In conclusion, an increase in the VPA dose resulted in a disproportional increase between dosage and C(total), whereas a proportional increase between dosage and C(free) still existed. Therefore, our study suggests that the therapeutic range of C(free) is 4 to 12 mg/L based on the therapeutic range of C(total) (45-100 mg/L) for general psychiatric conditions.

Population pharmacokinetics (P?PK) of valproic acid (VPA) following rapid infusion in epilepsy patients

Purpose Characterize VPA PopPK following rapid infusion. Methods: Epilepsy patients (N=112), with or without enzyme inducing comedications, were randomized to either 3.0 or 1.5 mg/kg/min 5-min VPA infusions. VPA plasma albumin binding was examined using 1 & 2 binding-site models. PopPK analysis of total & free plasma VPA concentrations (up to 6 h post-infusion) was performed using NONMEM. Effect of enzyme-induction on clearance (CL) and cholesterol, creatinine, age & inductions status on primary protein binding (PB) constant (K1) was examined using the chi-square test. Results: One & 2-comparment models optimally characterized total & free VPA concentrations, respectively. Estimated parameters±SE for uninduced subjects were: totalCL=1.21±0.0854 L/h, totalV=12.3±0.373 L, freeCL=18.4±8.17 L/h, freeV1=2.09±2.43 L, freeQ=63.7±61.7 L/h, & freeV2=65.8±25.7 L. Enzyme-induction was a significant covariate; totalCL & freeCL increased by 61 & 24%. VPA PB was nonlinear; 2-site PB model parameters±SE, viz., N1, K1, N2, & K2, were 1.54±0.108, 11.9±1.99 (1/mM), 0.194±0.0783, and 164±141 (1/mM). No significant covariates were identified for VPA PB. Inter-subject variabilities in totalCL, freeCL, & K1 were 45, 75 & 30%. Conclusions: These PopPK models accounting for induction status and albumin levels may be used to predict VPA concentrations. Accounting for other factors such as health status and genetics may reduce some of the unexplained variability and improve model predictability. Clinical Pharmacology & Therapeutics (2004) 75, P31–P31; doi: 10.1016/j.clpt.2003.11.116

Oral/intravenous maintenance dosing of valproate following intravenous loading: a simulation

Valproic acid (VPA) has a narrow therapeutic range (50–100 mg/l) and exhibits nonlinear protein binding. Additionally, VPA pharmacokinetics are dependent on age, induction status, and formulation; so titration and dosing vary between individuals. The aim of these simulations was to determine optimal intravenous (i.v.) loading dose, and i.v. and oral VPA maintenance regimens. A 5-min 15 mg/kg loading dose resulted in total and free plasma VPA concentrations of ∼65 and 7.5 mg/l in children, and ∼80 and 11 mg/l in adults, 1 h after the infusion; induction status had little effect. For uninduced children and adults, 7.5 and 3.5 mg/kg q6h i.v. valproate sodium, initiated 6 h after loading dose maintains therapeutic plasma VPA concentrations. The rapid decline of plasma VPA concentrations following an i.v. loading dose in combination with the delayed initial absorption of drug from delayed-release divalproex sodium tablets warrant beginning q12h oral maintenance regimens of delayed-release divalproex sodium within 2 h of a loading dose in the uninduced population. Plasma VPA concentrations can be sustained in the therapeutic range using once-daily maintenance regimens of extended-release divalproex sodium tablets if initiated concurrently with i.v. loading dose in the uninduced population. A two-fold higher i.v. and oral maintenance regimen dose may be required in induced patients.

Effect of heating human sera at a temperature necessary to deactivate human immunodeficiency virus on measurement of free phenytoin, free valproic acid, and free carbamazepine concentrations.

Minimizing the risk for infection to laboratory staff from a contaminated blood sample is a major safety goal in the clinical laboratory. One dangerous pathogen, the human immunodeficiency virus (HIV), can be deactivated by heating sera at 56 degrees C for 30 minutes. The authors previously reported that if serum was subjected to those conditions, the concentrations of the nine most commonly monitored drugs were not altered, whereas phenytoin and carbamazepine concentrations were reduced slightly. Monitoring free phenytoin, free valproic acid, and free carbamazepine concentrations is strongly recommended for patients with uremia, liver disease, and hypoalbuminemia. Because drug protein binding can be affected by temperature, the authors investigated the effect on free drug concentrations of sera heated to levels necessary for deactivation of the HIV virus. They measured total and free drug concentrations in serum pools prepared from patients receiving phenytoin, valproic acid, and carbamazepine. Serum pools were heated at 56 degrees C for 30 minutes and then brought to room temperature. The total and free drug concentrations were measured immediately after heating and then at 20- and 45-minute intervals. The concentrations of free phenytoin and free valproic acid were significantly higher after heat treatment. However, after equilibration of sera at room temperature for 20 minutes, the free concentrations of phenytoin were comparable to preheating values, although total phenytoin concentrations (Serum Separator Tubes) were reduced slightly. In contrast, free valproic acid concentrations did not return to the original levels even after 45 minutes. Free carbamazepine concentrations did not change even immediately after heating. However, total carbamazepine concentrations were reduced slightly when sera were heated in serum separator tubes (SST Tubes).

Effect of Carnitine on Valproic Acid Concentrations in Serum, Brain, and Liver

This study investigates the influence of l-carnitine supplementation on valproic acid concentrations in rat serum, brain, and liver. Carnitine supplementation increased carnitine concentrations significantly in serum and liver but not in the brain. Free valproic acid concentrations in the brain were significantly increased by carnitine supplementation without any change of carnitine concentrations in the brain. The increase of serum-free valproic acid concentrations by carnitine supplementation apparently caused brain-free valproic acid concentrations to increase. This study suggests that l-carnitine supplementation to valproic acid therapy may potentiate valproic acid effects in the brain, even when the clinical dosage in humans is used.

Elevated free phenytoin and free valproic acid concentrations in sera of patients infected with human immunodeficiency virus.

Seizures are common in patients infected with human immunodeficiency virus (HIV). Phenytoin and valproic acid are common anticonvulsants, and both drugs are strongly bound to serum albumin. Because patients infected with HIV are often on polytherapy, using homeopathic medicines, and may also have hypoalbuminemia, elevated free drug concentrations may occur in these patients. The authors prepared one serum pool from patients infected with HIV but receiving no bactrim and the other pool from HIV patients receiving bactrim. They supplemented both HIV pools and normal pool (diluted with 0.9% saline to mimic albumin concentration of HIV pools) with a known concentration of phenytoin or valproic acid. After incubation at 37 degrees C for 3 hours, they measured free phenytoin and free valproic acid concentrations in the protein free ultrafiltrates using fluorescence polarization immunoassays. The total drug concentrations in original sera were measured by microparticle enzyme immunoassays. None of the patients had any significant liver or renal disease. The aliquots of HIV pools and normal pool were supplemented with the same concentration of phenytoin or valproic acid. The concentration of free phenytoin and free valproic acid were significantly elevated in patients with HIV (mean = 2.52, SD = 0.11 micrograms/ml for phenytoin; mean = 41.5, SD = 1.5 micrograms/ml for valproate) compared to controls (mean = 1.50, SD = 0.0 7 micrograms/ml for phenytoin; mean = 19.9, SD = 0.5 micrograms/ml for valproate). The concentrations of both free phenytoin and valproic acid were further elevated in patients prepared in the HIV pool who were receiving bactrim (mean = 2.81, SD = 0.09 micrograms/ml for phenytoin; mean = 44.0, SD = 1.1 micrograms/ml for valproate), but when normal serum pool was supplemented with 4.4 mg/dl of bactrim (concentration of bactrim in HIV pool) and supplemented with the same concentration of phenytoin or valproic acid, the observed free concentrations were much lower (mean = 1.65, SD = 0.05 micrograms/ml for phenytoin; mean = 26.1, SD = 1.4 micrograms/ml for valproate). This indicates that hypoalbuminemia and bactrim concentrations do not account for the observed free drug concentrations in patients with HIV. The authors also observed elevated free phenytoin and valproic acid in sera from three individual patients with AIDS compared to normals (normal serum diluted with 0.9% saline to mimic the albumin concentration of serum collected from a patient with HIV and then both specimens supplemented with the same concentration of phenytoin or valproic acid.

Valproic acid-ketoconazole interaction in normal, hypoalbuminemic, and uremic sera: lack of interaction in uremic serum caused by the presence of inhibitor.

Ketoconazole is an antifungal agent widely used in the management of patients with fungal infection, especially in patients with acute acquired immuno-deficiency syndrome (AIDS). Ketoconazole is 99% bound to serum albumin and may interact with valproic acid, an anticonvulsant with 90% to 95% binding to serum albumin. The interaction may be more significant in hypoalbuminemia, a common finding in patients with AIDS. However, valproic acid-ketoconazole interaction has not been reported. The authors prepared two serum pools from patients receiving valproic acid with normal serum albumin and another pool from patients with hypoalbuminemia. Another serum pool was prepared from uremic patients not receiving valproic acid. The aliquots of serum pool were supplemented with various concentrations of ketoconazole, representing therapeutic and slightly higher therapeutic concentrations. The concentrations of free valproic acid were determined in protein-free ultrafiltrates (prepared by centrifuging specimens at 25 degrees C with the Centrifree Micropartition System at 1500 g for 20 minutes) using fluorescence polarization immunoassay. In the serum pool with normal albumin concentration, the authors observed statistically significant displacement of valproic acid only at higher ketoconazole concentrations (10 and 20 micrograms/ml) whereas, in the serum pool with hypoalbuminemia, they observed statistically significant displacement of valproic acid by ketoconazole with lower and higher concentrations of ketoconazole. The magnitude of displacement was more significant at high valproic acid concentrations (95 and 150 mg/ml, respectively) probably because of the concentration-dependent binding of valproic acid to serum albumin. The authors observed no displacement of valproic acid by ketoconazole in the uremic serum pool. On the other hand, the free valproic acid concentrations were decreased in the presence of ketoconazole in the uremic serum pool.

Elevated free fatty acid concentrations in lipemic sera reduce protein binding of valproic acid significantly more than phenytoin.

Higher concentrations of free valproic acid and phenytoin have been reported in patients with uremia and liver disease. Free fatty acids also displace valproic acid and phenytoin. This is a study of the magnitude of displacement of valproic acid and phenytoin from protein binding by free fatty acid in lipemic sera. Higher concentrations of free fatty acids in lipemic sera affected protein binding of valproic acid significantly more than that of phenytoin. Supplementing normal sera with free fatty acids also increased the free concentrations of both valproic acid and phenytoin as expected, but the observed effect was several times higher in magnitude with valproic acid. There was an increased free fraction of valproic acid in patients who received valproic acid and had hypertriglyceridemia. In a patient with uremia, there was also a significant increase in free valproic acid concentration after routine hemodialysis caused by an increase in free fatty acid concentration secondary to hemodialysis. Increased protein binding of valproic acid in sera was observed after treatment with activated charcoal because charcoal can remove free fatty acid. Because higher free fatty acid concentration significantly affects protein binding of valproic acid, careful monitoring of free valproic acid in patients with lipid disorder may be beneficial.

Elevated Free Fatty Acid Concentrations in Lipemic Sera Reduce Protein Binding of Valproic Acid Significantly More Than Phenytoin

AbstractHigher concentrations of free valproic acid and phenytoin have been reported in patients with uremia and liver disease. Free fatty acids also displace valproic acid and phenytoin. This is a study of the magnitude of displacement of valproic acid and phenytoin from protein binding by free fatty acid in lipemic sera. Higher concentrations of free fatty acids in lipemic sera affected protein binding of valproic acid significantly more than that of phenytoin. Supplementing normal sera with free fatty acids also increased the free concentrations of both valproic acid and phenytoin as expected, but the observed effect was several times higher in magnitude with valproic acid. There was an increased free fraction of valproic acid in patients who received valproic acid and had hypertriglyceridemia. In a patient with uremia, there was also a significant increase in free valproic acid concentration after routine hemodialysis caused by an increase in free fatty acid concentration secondary to hemodialysis. Increased protein binding of valproic acid in sera was observed after treatment with activated charcoal because charcoal can remove free fatty acid. Because higher free fatty acid concentration significantly affects protein binding of valproic acid, careful monitoring of free valproic acid in patients with lipid disorder may be beneficial.