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Pretorius E, van Zyl P, Joubert G. Therapeutic drug monitoring for valproate: deriving a novel formula for calculation of free concentration. Eur J Clin Pharmacol 2024:10.1007/s00228-024-03741-2. [PMID: 39150536 DOI: 10.1007/s00228-024-03741-2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2024] [Accepted: 08/08/2024] [Indexed: 08/17/2024]
Abstract
BACKGROUND Monitoring free valproate concentrations, as with other highly protein-bound anticonvulsants, is essential in clinical situations where protein binding may be disrupted. Conversion of measured total concentrations to approximate free concentrations offers a cost-effective alternative. This study evaluated the relationship between total and free valproate concentrations for discordance and the impact of key determinants. A novel formula was devised that incorporates significant variables. METHODS A multicentre, cross-sectional observational analytical study included 101 subjects 18 years and older using valproate for 6 months or longer. Participants were recruited from private and public sector healthcare settings from primary to tertiary level in, South Africa, during 2017-2019. RESULTS Free valproate concentrations could be measured for 84 subjects. Discordance for concomitant total and free valproate concentrations was 79.1%. Among 19 participants with elevated free concentrations, 15 (78.9%) had total valproate concentrations within the recommended reference range. Calculations based on the study-derived formula were more accurate in predicting free valproate concentration than previously proposed methods. CONCLUSION This study proposes that the novel formula for calculating free valproate enables more accurate prediction.
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Affiliation(s)
- Erna Pretorius
- Department of Pharmacology, Faculty of Health Sciences, University of the Free State, Bloemfontein, South Africa.
| | - Paulina van Zyl
- Department of Pharmacology, Faculty of Health Sciences, University of the Free State, Bloemfontein, South Africa
| | - Gina Joubert
- Department of Biostatistics, Faculty of Health Sciences, University of the Free State, Bloemfontein, South Africa
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The Effect of Plasma Protein Binding on the Therapeutic Monitoring of Antiseizure Medications. Pharmaceutics 2021; 13:pharmaceutics13081208. [PMID: 34452168 PMCID: PMC8401952 DOI: 10.3390/pharmaceutics13081208] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/10/2021] [Revised: 07/27/2021] [Accepted: 07/27/2021] [Indexed: 12/17/2022] Open
Abstract
Epilepsy is a widely diffused neurological disorder including a heterogeneous range of syndromes with different aetiology, severity and prognosis. Pharmacological treatments are based on the use, either in mono- or in polytherapy, of antiseizure medications (ASMs), which act at different synaptic levels, generally modifying the excitatory and/or inhibitory response through different action mechanisms. To reduce the risk of adverse effects and drug interactions, ASMs levels should be closely evaluated in biological fluids performing an appropriate Therapeutic Drug Monitoring (TDM). However, many decisions in TDM are based on the determination of the total drug concentration although measurement of the free fraction, which is not bound to plasma proteins, is becoming of ever-increasing importance since it correlates better with pharmacological and toxicological effects. Aim of this work has been to review methodological aspects concerning the evaluation of the free plasmatic fraction of some ASMs, focusing on the effect and the clinical significance that drug-protein binding has in the case of widely used drugs such as valproic acid, phenytoin, perampanel and carbamazepine. Although several validated methodologies are currently available which are effective in separating and quantifying the different forms of a drug, prospective validation studies are undoubtedly needed to better correlate, in real-world clinical contexts, pharmacokinetic monitoring to clinical outcomes.
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VandenBerg A, Broadway J, Lalich C, Kennedy R, Williams K. Valproate serum concentrations in patients with hypoalbuminemia and medical complications. Ment Health Clin 2018; 7:13-15. [PMID: 29955492 DOI: 10.9740/mhc.2017.01.013] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Introduction 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. Methods 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. Results 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. Discussion 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.
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Affiliation(s)
- Amy VandenBerg
- Clinical Pharmacy Specialist; Coordinator, Department of Pharmacy, Department of Psychiatry and Behavioral Sciences, Medical University of South Carolina, Charleston, South Carolina,
| | - Jessica Broadway
- Assistant Professor, Department of Psychiatry and Behavioral Sciences, Medical University of South Carolina, Charleston, South Carolina
| | - Callie Lalich
- Assistant Professor, Department of Psychiatry and Behavioral Sciences, Medical University of South Carolina, Charleston, South Carolina
| | - Rachel Kennedy
- PGY3 Psychiatry Resident, Department of Psychiatry and Behavioral Sciences, Medical University of South Carolina, Charleston, South Carolina
| | - Kristen Williams
- Assistant Professor, Department of Psychiatry and Behavioral Sciences, Medical University of South Carolina, Charleston, South Carolina
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Doré M, San Juan AE, Frenette AJ, Williamson D. Clinical Importance of Monitoring Unbound Valproic Acid Concentration in Patients with Hypoalbuminemia. Pharmacotherapy 2017; 37:900-907. [DOI: 10.1002/phar.1965] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Affiliation(s)
- Maxime Doré
- Department of Pharmacy; Hôpital du Sacré-Coeur de Montréal; Montreal Québec Canada
| | | | - Anne Julie Frenette
- Department of Pharmacy; Hôpital du Sacré-Coeur de Montréal; Montreal Québec Canada
- Research Center; Hôpital du Sacré-Coeur de Montréal; Montreal Québec Canada
- Faculty of Pharmacy; University of Montreal; Montreal Québec Canada
| | - David Williamson
- Department of Pharmacy; Hôpital du Sacré-Coeur de Montréal; Montreal Québec Canada
- Research Center; Hôpital du Sacré-Coeur de Montréal; Montreal Québec Canada
- Faculty of Pharmacy; University of Montreal; Montreal Québec Canada
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Riker RR, Gagnon DJ, Hatton C, May T, Seder DB, Stokem K, Fraser GL. Valproate Protein Binding Is Highly Variable in ICU Patients and Not Predicted by Total Serum Concentrations: A Case Series and Literature Review. Pharmacotherapy 2017; 37:500-508. [PMID: 28173638 DOI: 10.1002/phar.1912] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
STUDY OBJECTIVE The free fraction of valproate (the pharmacologically active moiety, normally 5-10%) may vary significantly in critically ill patients, but this topic is understudied, with only four prior intensive care unit (ICU) case reports. The objective of this study was to evaluate the range of valproate plasma protein binding in ICU patients. DESIGN Observational study of consecutive ICU patients. SETTING Neurocritical and medical critical care services in a nonuniversity academic medical center. PATIENTS Consecutive ICU patients treated with valproate with serum albumin less than 4 g/dl. MEASUREMENTS AND MAIN RESULTS Simultaneous total and free trough serum valproate concentrations were measured as were serum creatinine, blood urea nitrogen, albumin, platelets, and transaminase values. The reference concentration range was 50-125 mg/L (total) and 5-17 mg/L (free). Valproate concentrations were categorized as within reference range, low, or high, and as concordant if both concentrations were in the same category. Data are reported as median (interquartile range). Fifteen patients (nine men) were evaluated. The median age was 63 (34-70) years. The valproate dose was 3 g/day (35 mg/kg/day). No patient had a valproate free fraction of 5-10%; the median was 48%, and the range was 15-89%. Total and free concentrations showed poor correlation (0.43) and were concordant in only two patients (both in the reference range). Free valproate concentration was poorly predicted by an equation correcting for albumin (r = 0.45). Suspected adverse drug events occurred in 10 patients: hyperammonemia in 7 of 12 tested (58%), elevated transaminases in 2 of 15 (13%), and thrombocytopenia in 5 of 15 (33%). CONCLUSIONS Protein binding of valproate was highly inconsistent in this cohort of ICU patients, and total valproate concentrations did not predict free concentrations, even when correcting for albumin. Additional research to define best practice for dosing and monitoring valproate and the relationship between free valproate concentrations and clinical or adverse effects in ICU patients is needed.
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Affiliation(s)
- Richard R Riker
- Critical Care Medicine, Maine Medical Center, Portland, Maine.,Neurocritical Care and Neuroscience Institute, Maine Medical Center, Portland, Maine
| | - David J Gagnon
- Department of Pharmacy, Maine Medical Center, Portland, Maine
| | - Colman Hatton
- Department of Emergency Medicine, University of Michigan School of Medicine, Ann Arbor, Michigan
| | - Teresa May
- Critical Care Medicine, Maine Medical Center, Portland, Maine.,Neurocritical Care and Neuroscience Institute, Maine Medical Center, Portland, Maine
| | - David B Seder
- Critical Care Medicine, Maine Medical Center, Portland, Maine.,Neurocritical Care and Neuroscience Institute, Maine Medical Center, Portland, Maine
| | - Katie Stokem
- Critical Care Medicine, Maine Medical Center, Portland, Maine.,Neurocritical Care and Neuroscience Institute, Maine Medical Center, Portland, Maine
| | - Gilles L Fraser
- Critical Care Medicine, Maine Medical Center, Portland, Maine.,Department of Pharmacy, Maine Medical Center, Portland, Maine
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Chatzistefanidis D, Lazaros L, Giaka K, Nakou I, Tzoufi M, Georgiou I, Kyritsis A, Markoula S. UGT1A6- and UGT2B7-related valproic acid pharmacogenomics according to age groups and total drug concentration levels. Pharmacogenomics 2016; 17:827-35. [PMID: 27232006 DOI: 10.2217/pgs-2016-0014] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
AIM The role of UGT1A6 and UGT2B7 polymorphisms and the impact of total drug plasma concentration in valproic acid (VPA) pharmacogenomics. PATIENTS & METHODS A total of 134 Greek patients were recruited (76 adults). Patients were genotyped for UGT1A6 19T>G, 541A>G and 552A>C and UGT2B7 802T>C polymorphisms. Patients' demographic and clinical data were registered. Natural logarithm of concentration-to-dose ratio (CDR) was also calculated as the final outcome. RESULTS No significant genotype-related differences in VPA metabolism were noted among various subgroups. An increased lnCDR ratio was noted in children patients compared with adults suggesting increased metabolic capability in younger ages. CONCLUSION UGT1A6 and UGT2B7 genotypes were not related to significant changes in VPA metabolism, even after controlling for total drug concentration levels. Younger ages were associated with increased VPA clearance rate.
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Affiliation(s)
| | - Leandros Lazaros
- Medical Genetics & Assisted Reproduction, University of Ioannina, Ioannina, Greece
| | - Katerina Giaka
- Medical Genetics & Assisted Reproduction, University of Ioannina, Ioannina, Greece
| | - Iliada Nakou
- Department of Pediatrics, University of Ioannina, Stavros Niarchos Avenue, 45500 Ioannina, Greece
| | - Meropi Tzoufi
- Department of Pediatrics, University of Ioannina, Stavros Niarchos Avenue, 45500 Ioannina, Greece
| | - Ioannis Georgiou
- Medical Genetics & Assisted Reproduction, University of Ioannina, Ioannina, Greece
| | | | - Sofia Markoula
- Department of Neurology, University of Ioannina, Ioannina, Greece
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Klein S, Maggioni S, Bucher J, Mueller D, Niklas J, Shevchenko V, Mauch K, Heinzle E, Noor F. In Silico Modeling for the Prediction of Dose and Pathway-Related Adverse Effects in Humans From In Vitro Repeated-Dose Studies. Toxicol Sci 2015; 149:55-66. [PMID: 26420750 DOI: 10.1093/toxsci/kfv218] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Long-term repeated-dose toxicity is mainly assessed in animals despite poor concordance of animal data with human toxicity. Nowadays advanced human in vitro systems, eg, metabolically competent HepaRG cells, are used for toxicity screening. Extrapolation of in vitro toxicity to in vivo effects is possible by reverse dosimetry using pharmacokinetic modeling. We assessed long-term repeated-dose toxicity of bosentan and valproic acid (VPA) in HepaRG cells under serum-free conditions. Upon 28-day exposure, the EC50 values for bosentan and VPA decreased by 21- and 33-fold, respectively. Using EC(10) as lowest threshold of toxicity in vitro, we estimated the oral equivalent doses for both test compounds using a simplified pharmacokinetic model for the extrapolation of in vitro toxicity to in vivo effect. The model predicts that bosentan is safe at the considered dose under the assumed conditions upon 4 weeks exposure. For VPA, hepatotoxicity is predicted for 4% and 47% of the virtual population at the maximum recommended daily dose after 3 and 4 weeks of exposure, respectively. We also investigated the changes in the central carbon metabolism of HepaRG cells exposed to orally bioavailable concentrations of both drugs. These concentrations are below the 28-day EC(10) and induce significant changes especially in glucose metabolism and urea production. These metabolic changes may have a pronounced impact in susceptible patients such as those with compromised liver function and urea cycle deficiency leading to idiosyncratic toxicity. We show that the combination of modeling based on in vitro repeated-dose data and metabolic changes allows the prediction of human relevant in vivo toxicity with mechanistic insights.
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Affiliation(s)
- Sebastian Klein
- *Biochemical Engineering, Saarland University, 66123 Saarbruecken, Germany
| | - Silvia Maggioni
- IRCCS - Instituto di Ricerche Farmacologiche "Mario Negri," 20156 Milan, Italy
| | - Joachim Bucher
- Insilico Biotechnology AG, 70563 Stuttgart, Germany, and
| | - Daniel Mueller
- *Biochemical Engineering, Saarland University, 66123 Saarbruecken, Germany
| | - Jens Niklas
- Insilico Biotechnology AG, 70563 Stuttgart, Germany, and
| | | | - Klaus Mauch
- Insilico Biotechnology AG, 70563 Stuttgart, Germany, and
| | - Elmar Heinzle
- *Biochemical Engineering, Saarland University, 66123 Saarbruecken, Germany
| | - Fozia Noor
- *Biochemical Engineering, Saarland University, 66123 Saarbruecken, Germany,
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[Clinical pharmacology and aging]. Presse Med 2013; 42:171-80. [PMID: 23332403 DOI: 10.1016/j.lpm.2012.06.023] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/18/2012] [Revised: 05/24/2012] [Accepted: 06/06/2012] [Indexed: 01/10/2023] Open
Abstract
Clinicians must be aware that aging can lead to changes in the pharmacokinetics and pharmacodynamics of many drugs. Drug distribution may be modified with aging secondarily to the decrease of serum albumin and to modifications of body composition (increase in the proportion of fat mass and decrease of lean mass). Hepatic metabolism of several drugs is reduced with age, especially drugs which depend of hepatic blood flow or P450 cytochroms. The incidence of renal failure increase largely with age. Glomerular filtration rate should be systematically estimated in older patients and, when needed, the doses of those drugs having significant renal elimination should be adjusted. In older patients, changes in the response to drugs can also develop, concerning specially the central nervous system (increased sensibility to any neurological effect of drugs), the cardiovascular system and the renal management of water and electrolytes. In many cases, the pharmacological changes associated to age are mild and requires no dose adjustment. However, many drugs should be adapted depending on the individual situation of each patient, particularly his renal function and nutritional state. Finally, some drugs should be avoided in older patients because of a bad effectiveness/tolerance ratio compared to alternatives.
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