Free serum valproate concentration more reliable than total concentration in critically ill patients

Clinical Pharmacokinetic Monitoring of Free Valproic Acid Levels: A Systematic Review

BACKGROUND

Current guidelines recommend therapeutic drug monitoring as a critical component of valproic acid (VPA) therapy. Due to high protein binding, the active unbound (free) portion of VPA can be misrepresented by total VPA serum levels in certain clinical scenarios. Monitoring free VPA serum levels may be warranted when assessing the clinical response to VPA therapy.

OBJECTIVES

The aims were to conduct a systematic review to identify a therapeutic range for free VPA serum levels; to explore the correlation of free VPA serum levels with clinical toxicity and therapeutic benefit; and to examine predictors of discordance between free and total VPA levels.

METHODS

Medline, EMBASE, Cochrane Central Register of Controlled Trials (CENTRAL), PsycINFO, BIOSIS Previews, and Cumulative Index to Nursing and Allied Health Literature (CINAHL) were searched from the time of database inception to June 20, 2021. Randomized controlled trials and observational studies that evaluated any patient receiving VPA with free VPA level monitoring were included.

RESULTS

Of 189 citations, we identified 27 relevant studies, which included 14 observational studies, two case series, and 11 case reports. Three studies provided a therapeutic range for free VPA levels between 20 and 410 μmol/L. Two studies suggested the occurrence of hyperammonemia and thrombocytopenia at free VPA serum levels above 60 µmol/L and 103.3 µmol/L, respectively. Two studies suggested an upper limit for neurotoxicity at free VPA serum levels of 70 µmol/L and 207.9 µmol/L. Hypoalbuminemia was identified as a predictor of therapeutic discordance.

CONCLUSIONS

This review demonstrates a paucity of data informing the clinical utility of free VPA serum levels. Further high-quality trials are needed to validate an optimal therapeutic range for free VPA levels.

Predicting the occurrence of thrombocytopenia from free valproate levels: A prospective study

PURPOSE

The likelihood of valproate (VPA) induced thrombocytopenia increases with higher VPA levels. In critically ill patients, the biological active free VPA level cannot be predicted from the total serum level. In this study, we evaluated the relationship between trough free VPA serum levels and concomitant platelet counts and assessed risk factors for the development of thrombocytopenia with the aim of generating a formula specifying the probabilities of developing thrombocytopenia based on trough free serum VPA levels.

METHODS

Trough free VPA levels and concomitant platelet counts were collected from a large cohort of patients who participated in a prospective VPA monotherapy trial. Significant variables associated with thrombocytopenia in a univariate analysis were evaluated in a multivariate model. A receiver operator curve was performed to compute the trough free VPA levels with the greatest discriminating power in predicting thrombocytopenia.

RESULTS

844 trough free VPA levels and concomitant platelet counts obtained from 264 patients were analyzed. In a multivariate analysis, trough free VPA levels, gender, and baseline platelet counts were significantly associated with thrombocytopenia. Using stepwise regression and multivariate logistic regression analyses, we generated gender-specific formulas for predicting platelet counts and probabilities of developing thrombocytopenia. The trough free VPA with the greatest discriminating power to predict platelet values ≤ 100,000/μL was 16.65 µg/mL.

CONCLUSIONS

The generated model was based on trough free VPA levels and achieved high sensitivity and specificity. Our results are therefore generalizable and can be applied to estimate the probability of developing thrombocytopenia in critically ill patients.

Therapeutic drug monitoring of valproic acid in extracorporeal membrane oxygenation

INTRODUCTION

Extracorporeal membrane oxygenation (ECMO) is a life-saving therapy for those in cardiopulmonary failure, including post-cardiac arrest. Despite a high volume of ECMO patients using anti-seizure medication, there is a paucity of data concerning the dosing, levels, and clinical scenarios for their use.

CASE REPORT

We present three cases of ECMO patients post-PEA arrest who were on valproic acid (VPA) for treatment of seizure and/or myoclonus. The total and free levels of VPA are reported.

DISCUSSION

The trough levels are consistent throughout therapy, suggesting VPA is not significantly removed by the ECMO circuitry. Although the total serum levels remained below the toxic range, the free level was elevated in two patients. These patients did not develop signs of toxicity.

CONCLUSION

VPA may be an effective anti-seizure medication in ECMO patients. Free VPA levels should be more readily available to better quantify efficacy or toxicity, especially in ECMO patients.

The Evolving Paradigm of Individualized Postresuscitation Care After Cardiac Arrest

The postresuscitation period after a cardiac arrest is characterized by a wide range of physiological derangements. Variations between patients include preexisting medical problems, the underlying cause of the cardiac arrest, presence or absence of hemodynamic and circulatory instability, severity of the ischemia-reperfusion injury, and resuscitation-related injuries such as pulmonary aspiration and rib or sternal fractures. Although protocols can be applied to many elements of postresuscitation care, the widely disparate clinical condition of cardiac arrest survivors requires an individualized approach that stratifies patients according to their clinical profile and targets specific treatments to patients most likely to benefit. This article describes such an individualized approach, provides a practical framework for evaluation and triage at the bedside, and reviews concerns specific to all members of the interprofessional postresuscitation care team.

Valproate for agitation in critically ill patients: A retrospective study

PURPOSE

The purpose was to describe the use of valproate therapy for agitation in critically ill patients, examine its safety, and describe its relationship with agitation and delirium.

MATERIALS AND METHODS

This retrospective cohort study evaluated critically ill adults treated with valproate for agitation from December 2012 through February 2015. Information on valproate prescribing practices and safety was collected. Incidence of agitation, delirium, and concomitant psychoactive medication use was compared between valproate day 1 and valproate day 3. Concomitant psychoactive medication use was analyzed using mixed models.

RESULTS

Fifty-three patients were evaluated. The median day of valproate therapy initiation was ICU day 7, and it was continued for a median of 7 days. The median maintenance dose was 1500 mg/d (23 mg/kg/d). The incidence of agitation (96% vs 61%, P < .0001) and delirium (68% vs 49%, P = .012) significantly decreased by valproate day 3. Treatment with opioids (77% vs 65%, P = .02) and dexmedetomidine (47% vs 24%, P = .004) also decreased. In mixed models analyses, valproate therapy was associated with reduced fentanyl equivalents (-185 μg/d, P = .0003) and lorazepam equivalents (-2.1 mg/d, P = .0004). Hyperammonemia (19%) and thrombocytopenia (13%) were the most commonly observed adverse effects.

CONCLUSIONS

Valproate therapy was associated with a reduction in agitation, delirium, and concomitant psychoactive medication use within 48 hours of initiation.