Valproate, carnitine metabolism, and biochemical indicators of liver function. Collaborative Group for the Study of Epilepsy

Valproic Acid-Associated Hyperammonemia: A Systematic Review

BACKGROUND

Hyperammonemia is an adverse effect that poses clinical uncertainty around valproic acid (VPA) use. The prevalence of symptomatic and asymptomatic hyperammonemia and its relationship to VPA concentration is not well established. There is also no clear guidance regarding its management. This results in variability in the monitoring and treatment of VPA-induced hyperammonemia. To inform clinical practice, this systematic review aims to summarize evidence available around VPA-associated hyperammonemia and its prevalence, clinical outcomes, and management.

METHODS

An electronic search was performed through Ovid MEDLINE, Ovid Embase, Web of Science, and PsycINFO using search terms that identified hyperammonemia in patients receiving VPA. Two reviewers independently performed primary title and abstract screening with a third reviewer resolving conflicting screening results. This process was repeated during the full-text review process.

RESULTS

A total of 240 articles were included. Prevalence of asymptomatic hyperammonemia (5%-73%) was higher than symptomatic hyperammonemia (0.7%-22.2%) and occurred within the therapeutic range of VPA serum concentration. Various risk factors were identified, including concomitant medications, liver injury, and defects in carnitine metabolism. With VPA discontinued, most symptomatic patients returned to baseline mental status with normalized ammonia level. There was insufficient data to support routine monitoring of ammonia level for VPA-associated hyperammonemia.

CONCLUSIONS

Valproic acid-associated hyperammonemia is a common adverse effect that may occur within therapeutic range of VPA. Further studies are required to determine the benefit of routine ammonia level monitoring and to guide the management of VPA-associated hyperammonemia.

Blood Levels of Ammonia and Carnitine in Patients Treated with Valproic Acid: A Meta-analysis

Objective

Long-term valproic acid (VPA) administration is associated with adverse metabolic effects, including hyperammonemia and hypocarnitinemia. However, the pathogeneses of these adverse events remain unclear, and not enough reviews have been performed. The aim of this study was to conduct a meta-analysis of studies examining blood levels of ammonia and carnitine in patients treated with VPA.

Methods

We conducted database searches (PubMed, Web of Science) to identify studies examining blood levels of ammonia and carnitine in patients treated with VPA. A meta-analysis was performed to conduct pre- and post-VPA treatment comparisons, cross-sectional comparisons between groups with and without VPA use, and estimations of the standardized correlations between blood levels of ammonia, carnitine, and VPA.

Results

According to the cross-sectional comparisons, the blood ammonia level in the VPA group was significantly higher than that in the non-VPA group. Compared to that in the non-VPA group, the blood carnitine level in the VPA group was significantly lower. In the meta-analysis of correlation coefficients, the blood VPA level was moderately correlated with blood ammonia and blood free carnitine levels in the random effects model. Furthermore, the blood ammonia level was moderately correlated with the blood free carnitine level.

Conclusion

Although the correlation between ammonia and free carnitine levels in blood was significant, the moderate strength of the correlation does not allow clinicians to infer free carnitine levels from the results of ammonia levels. Clinicians should measure both blood ammonia and free carnitine levels, especially in patients receiving high dosages of VPA.

The correlation between carbamazepine and valproic acid monotherapy with serum adiponectin and carnitine

Antiepileptic drugs may cause systemic and metabolic side effects. The aim of our study was to investigate the effects of valproic acid and carbamazepine monotherapy used in the treatment of epilepsy patients on serum adiponectin and carnitine levels. The study included 60 patients, of which 30 patients receiving valproic acid monotherapy and 30 patients receiving carbamazepine monotherapy, who were followed up by the epilepsy outpatient clinic with the diagnosis of idiopathic epilepsy, and 30 healthy volunteers. Patients, who used drugs for at least 6 months, were selected. Venous blood samples were collected from the patients and healthy volunteers after their consent was obtained. Serum carnitine and adiponectin levels in the collected samples were measured using the ELISA method. Serum carnitine levels were 5166.55 ng/ml (± 1954.92) in patients receiving carbamazepine, 4224.56 ng/ml (± 2055.54) in patients using valproic acid, and 5802.64 ng/ml (± 3422.57) in the control group. Serum adiponectin levels were 13,606.51 ng/ml (± 5915.92) in patients using carbamazepine, 11,986.58 ng/ml (± 5367.82) in patients receiving valproic acid, and 14,033.43 ng/ml (± 5646.34) in the control group. In both groups, both serum carnitine and serum adiponectin levels were lower than the control group. There was a negative but insignificant correlation between the duration and dose of carbamazepine and valproic acid drug use and serum adiponectin and carnitine levels. There is a need for more extensive studies with larger sample size to investigate the effect of antiepileptic drugs used on serum adiponectin and carnitine levels.

An Examination of Serum Acylcarnitine and Amino Acid Profiles at Different Time Point of Ketogenic Diet Therapy and Their Association of Ketogenic Diet Effectiveness

Background: This study aimed to identify metabolic parameters at different time points of ketogenic diet therapy (KDT) and investigate their association with response to KDT in pediatric drug-resistant epilepsy (DRE). Methods: Prospectively, twenty-nine patients (0.67~20 years old) with DRE received classic ketogenic diet with non-fasting, gradual KD initiation protocol (GRAD-KD) for 1 year were enrolled. A total of 22 patients remaining in study received blood examinations at baseline, 3rd, 6th, 9th, and 12th months of KDT. β-hydroxybutyrate, free carnitine, acylcarnitines, and amino acids were compared between responders (seizure reduction rate ≥ 50%) and non-responders (seizure reduction rate < 50%) to identify the effectiveness of KDT. Results: The 12-month retention rate was 76%. The responders after 12 months of KDT were 59% (13/22). The free carnitine level decreased significantly at 9th months (p < 0.001) but increased toward baseline without symptoms. Propionyl carnitine (C3), Isovaleryl carnitine (C5), 3-Hydroxyisovalerylcarnitine (C5:OH) and methylmalonyl carnitine (C4-DC) decreased but 3-hydroxybutyrylcarnitine (C4:OH) increased significantly at 12th months of KDT. The glycine level was persistently higher than baseline after KDT. KDT responders had lower baseline C3 and long-chain acylcarnitines, C14 and C18, as well as lower C5, C18, and leucine/isoleucine. Conclusions: KDT should be avoided in patients with non-ketotic hyperglycemia. Routine carnitine supplementation is not recommended because hypocarnitinemia was transient and asymptomatic during KDT. Better mitochondrial βoxidation function associates with greater KDT response.

[The decreased level of plasma carnitine in patients with epilepsy]

Antiepileptic drugs (AEDs) have long been known to affect carnitine metabolism, dropping the plasma free carnitine. Valproate (VPA) was considered to be the strongest carnitine-reducing agent. VPA-induced hyperammonemic encephalopathy and hepatotoxicity are well known, and pre-existing carnitine deficiency can be a predisposing factor, especially in congenital metabolic disorders. Several studies have shown that carnitine supplementation in patients receiving VPA to result in subjective and objective improvements and to prevent VPA-induced hepatotoxicity and encephalopathy, in parallel with increases in carnitine serum concentrations. Level of free plasma carnitine <20 micromol/l (syn. carnitine deficiency) in patients with epilepsy (in 15-30% of cases) may occur not only with administration of VPA but with administration of other AEDs (phenobarbital, phenytoin, carbamazepine) and low nutritional intake of carnitine. Some findings indicate that the number of AEDs used is a risk factor for carnitine deficiency. It was established that body weight, height and multidrug therapy are significantly associated with low level of free plasma in epileptic patients. Carnitine deficiency can have severe consequences; but most epileptic patients suffering from it are asymptomatic. Although carnitine deficiency is not uncommon among patients receiving AEDs, it seems not necessary to routinely monitor carnitine levels in epileptic ambulatory patients, this is reasonable only in groups of risk. L-carnitine supplementation is clearly indicated in case of VPA-induced hepatotoxicity (i.v. administration) VPA overdose (i.v. administration), primary carnitine-transporter defect and is strongly recommended in specific secondary carnitine deficiency syndromes, symptomatic VPA-associated hyperammonemia, infants and young children receiving VPA, especially those younger than 2 years, patients with a complex neurologic disorder, who are receiving multiple AEDs, patients who have risk factors for hepatotoxicity and carnitine insufficiency. In the absence of double blind trials, clinical practice is based on empiric observation, clinical experience, and theory. Well-designed studies of specific and general uses of L-carnitine replacement therapy in patients with epilepsy are needed.

Screening of carnitine and biotin deficiencies on tandem mass spectrometry

BACKGROUND

It is important to assess pediatric patients for nutritional deficiency when they are receiving specific interventions, such as enteral feeding. We focused on measurement of C0 and 3-hydroxyisovalerylcarnitine (C5-OH) with tandem mass spectrometry (MS/MS), which is performed as part of the newborn mass screening. The purpose of this study was to investigate the usefulness of MS/MS for screening carnitine and biotin deficiencies.

METHODS

Forty-two children (24 boys, 18 girls) were enrolled between December 2013 and December 2015. Blood tests, including measurement of serum free carnitine via the enzyme cycling method, and acylcarnitine analysis on MS/MS of dried blood spot (DBS), were performed for the evaluation of nutrition status.

RESULTS

Median patient age was 2 years (range, 2 months-14 years). Mean serum free carnitine was 41.8 ± 19.2 μmol/L. In six of the 42 patients, serum free carnitine was <20 μmol/L (range, 4.0-18.7 μmol/L). C0 and C5-OH measured on MS/MS of DBS were 33.8 ± 20.2 nmol/mL and 0.48 ± 0.22 nmol/mL, respectively. There was a strong positive correlation (r = 0.89, P < 0.001) between serum free carnitine and C0 measured on the same day. In one patient on hydrolyzed formula, C5-OH was >1.00 nmol/L. Therapy-resistant eczema was improved by treatment with additional biotin and a non-hydrolyzed formula.

CONCLUSION

C0 and C5-OH, measured on MS/MS of DBS, were useful for screening carnitine and biotin deficiencies.

Carnitine deficiency: Risk factors and incidence in children with epilepsy

BACKGROUND

Carnitine deficiency is relatively common in epilepsy; risk factors reportedly include combination antiepileptic drug (AED) therapy with valproic acid (VPA), young age, intellectual disability, diet and enteral or parenteral feeding. Few studies have examined the correlation between each risk factor and carnitine deficiency in children with epilepsy. We examined the influence of these risk factors on carnitine deficiency, and identified a formula to estimate plasma free carnitine concentration in children with epilepsy.

METHODS

Sixty-five children with epilepsy and 26 age-matched controls were enrolled. Plasma carnitine concentrations were measured using an enzyme cycling assay, and correlations were sought with patients' other clinical characteristics.

RESULTS

Carnitine deficiency was found in approximately 17% of patients with epilepsy and was significantly associated with carnitine-free enteral formula only by tube feeding, number of AEDs taken (independent of VPA use), body weight (BW), body height and Gross Motor Function Classification System (GMFCS) score. Stepwise multiple linear regression analysis indicated that carnitine concentration (in μmol/L) could be accurately estimated from a formula that does not require blood testing: 42.44+0.14×(BW in kg)-18.16×(feeding)-3.19×(number of AEDs), where feeding was allocated a score of 1 for carnitine-free enteral formula only by tube feeding and 0 for taking food orally (R(2)=0.504, P<0.001).

CONCLUSIONS

Carnitine-free enteral formula only by tube feeding, multiple AED treatment and low BW are risk factors for carnitine deficiency in children with epilepsy. l-carnitine should be administered to children at risk of deficiency to avoid complications. Treatment decisions can be informed using an estimation formula that does not require blood tests.

Metabolomics study with gas chromatography-mass spectrometry for predicting valproic acid-induced hepatotoxicity and discovery of novel biomarkers in rat urine

Three different doses of valproic acid (20, 100, and 500 mg/kg/d) are administered orally to Sprague-Dawley rats for 5 days, and the feasibility of metabolomics with gas chromatography-mass spectrometry as a predictor of the hepatotoxicity of valproic acid is evaluated. Body weight is found to decrease with the 100-mg/kg/d dose and significantly decrease with the 500-mg/kg/d dose. Mean excreted urine volume is lowest in the 500-mg/kg/d group among all groups. The plasma level of alpha-glutathione-S-transferase, a sensitive and earlier biomarker for hepatotoxicity, increases significantly with administration of 100 and 500 mg/kg/d; however, there is not a significant difference in alpha-glutathione-S-transferase plasma levels between the control and 20-mg/kg/d groups. Clusters in partial least squares discriminant analysis score plots show similar patterns, with changes in physiological conditions and plasma levels of alpha-glutathione-S-transferase; the cluster for the control and 20-mg/kg/d groups does not clearly separate, but the clusters are separate for 100- and 500-mg/kg/d groups. A biomarker of hepatotoxicity, 8-hydroxy-2'-deoxyguanosine and octanoylcarnitine, is identified from nontargeted and targeted metabolic profiling. These results validate that metabolic profiling using gas chromatography-mass spectrometry could be a useful tool for finding novel biomarkers. Thus, a nontargeted metabolic profiling method is established to evaluate the hepatotoxicity of valproic acid and demonstrates proof-of-concept that metabolomic approach with gas chromatography-mass spectrometry has great potential for predicting valproic acid-induced hepatotoxicity and discovering novel biomarkers.

Serum and muscle carnitine levels in epileptic children receiving sodium valproate

The purpose of this study was to determine whether children with epilepsy undergoing valproate therapy and who are otherwise healthy have lower levels of serum and muscle carnitine. A total of 50 patients with epilepsy, 3 to 14 years of age, who were treated solely with valproate and free of abnormal neurologic findings or nutritional problems were selected. The control group consisted of 30 healthy children. The total carnitine levels in serum were 28.1 +/- 10.3 and 55.6 +/-7.3 microg/mL, and the free carnitine levels in serum were 16.5 +/-10.2 and 44.6 +/-7.3 microg/mL, the total carnitine levels in muscle were 12.1 +/- 1.8 and 45.3 +/- 5.9 micromol/g noncollagen protein and the free carnitine levels in muscle were 5.6 +/- 1.6 and 39.3 +/- 6.0 micromol/g noncollagen protein in the valproic acid-treated and control groups, respectively (P < .05). In conclusion, valproate monotherapy depletes both muscle and serum carnitine levels in otherwise healthy epileptic children.

Vigabatrin, lamotrigine, topiramate and serum carnitine levels

Clinical studies indicate a decrease in free and total carnitine in children treated with old-generation antiepileptic drugs (especially valproate). Here, we studied the effect of new-generation antiepileptic drugs on serum carnitine levels. Serum carnitine levels were measured in 91 children: 24 treated with vigabatrin, 28 treated with lamotrigine, and 21 treated with topiramate. These drugs were given as monotherapy (54 children) or polytherapy (19 children). Eighteen additional children treated with valproate served as control subjects. Reduced mean serum carnitine level was evident only in children treated with valproate, with mean free and total carnitine level of 26.9 +/- 8.6 micromol/L and 29.1 +/- 10.4 micromol/L, respectively. In contrast, the mean serum carnitine levels of children treated with vigabatrin, lamotrigine, or topiramate were similar and normal. In these children, the free carnitine levels were 38.5 +/- 7.8 micromol/L, 37.2 +/- 7.7 microg/mL, and 40.4 +/- 8.7 micromol/L, respectively, and total carnitine levels were 43.5 +/- 8.8 micromol/L, 44.4 +/- 9.2 micromol/L, and 45.5 +/- 9.8 micromol/L (+/-S.D.), respectively. Only 4 children (treated with valproate) exhibited considerably lower serum carnitine levels. None of these children had significant clinical adverse effects attributable to carnitine deficiency. In conclusion, these new-generation antiepileptic drugs probably do not cause carnitine deficiency. In contrast, valproate may induce carnitine deficiency, but most cases are asymptomatic.

Valproate as a mainstay of therapy for pediatric epilepsy

This article reviews relevant pharmacologic and clinical information gathered for valproate since it was introduced into clinical practice 37 years ago and the application of this information for the treatment of childhood epilepsy. Valproate is available for oral and parenteral use. Oral forms are almost completely bioavailable but the rate of absorption varies between formulations. The Chrono tablet formulation has not been adapted for children aged <6 years, in whom the oral solution or syrup, requiring two or three daily administrations, has been used until recently. A new formulation specifically adapted for children, Chronosphere, administrated once or twice daily, is a modified-release formulation of valproate that minimizes fluctuations in serum drug concentrations during a dosage interval. Plasma protein binding is 80-94% and tends to decrease with increasing drug concentration. Valproate elimination is markedly decreased in newborns compared with older children and adults. Elimination by glucuronidation only becomes fully effective by the age of 3-4 years. In children aged 2-10 years receiving valproate, plasma clearances are 50% higher than those in adults. Over the age of 10 years, pharmacokinetic parameters approximate those of adults. Valproate can increase plasma concentrations of concomitant drugs, such as phenobarbital and lamotrigine, by inhibiting their metabolism. As a result of its broad spectrum of efficacy in a wide range of seizure types and epilepsy syndromes, valproate is a drug of choice for children with newly diagnosed epilepsy (focal or generalized), idiopathic generalized epilepsy, epilepsies with prominent myoclonic seizures or with multiple seizure types, and photosensitive epilepsies. In the group of cognitive epilepsies, in which severe spike and wave discharges are accompanied by cognitive deterioration, valproate, ethosuximide, or both should be tested before using corticosteroids. In comparative trials with carbamazepine, phenytoin, and phenobarbital in focal epilepsy and with ethosuximide in absence epilepsy, valproate was as effective and showed a favorable tolerability profile, with minimal adverse cognitive and CNS effects. The low potential for paradoxical seizure aggravation and the long-term efficacy of the drug are additional important factors that contribute to its excellent profile. Intravenous valproate may be effective for the treatment of convulsive and non-convulsive status epilepticus that is refractory to conventional drugs. In infants, potential benefits should be carefully weighed against the risk of liver toxicity. Gastrointestinal intolerance is a relatively frequent, dose-related adverse effect of the drug in children. Bodyweight increase and tremor may be observed in older children and adolescents. Despite the challenge of newer drugs, valproate remains a gold standard antiepileptic drug for the treatment of children.

Effect of sodium valproate monotherapy on serum uric acid concentrations in ambulatory epileptic children: a prospective long-term study

PURPOSE

Hyperuricemia has been shown to be related to cardiovascular morbidity and mortality. There is controversial data about the effect of sodium valproate (VPA) monotherapy on serum uric acid concentrations. The purpose of this study was to investigate by a long-term, prospective method, whether treatment with VPA monotherapy may alter serum uric acid concentrations and liver function tests in ambulatory epileptic children.

MATERIAL AND METHODS

Serum uric acid concentrations were determined in 28 ambulatory epileptic children before and at 6, 12 and 24 months of VPA monotherapy. Serum concentrations of biochemical markers of liver and renal function, such as alanine aminotransferase (ALT), aspartate aminotransferase (AST), lactate dehydrogenase (LDH), gamma-glutamyltransferase (gamma-GT) and creatinine (Cr) were also measured before and at 6, 12 and 24 months of VPA monotherapy. Serum VPA concentrations remained within the therapeutic range (50-100 mg/L) during the period of study.

RESULTS

No statistically significant changes in serum uric acid concentrations were found at 6, 12 or 24 months of treatment. Serum ALT concentrations were significantly increased at 6 and 12 months of treatment, AST concentrations at 6 and 12 months of treatment and LDH concentrations at 12 months of treatment.

CONCLUSIONS

VPA monotherapy does not have a significant effect on serum uric acid concentrations in ambulatory epileptic children. Further studies are needed to definitively address whether it would be useful for physicians to routinely check for elevated serum uric acid levels in children treated with VPA.

Plasma free carnitine in epilepsy children, adolescents and young adults treated with old and new antiepileptic drugs with or without ketogenic diet

This study was performed to evaluate carnitine deficiency in a large series of epilepsy children and adolescents treated with old and new antiepileptic drugs with or without ketogenic diet. Plasma free carnitine was determined in 164 epilepsy patients aged between 7 months and 30 years (mean 10.8 years) treated for a mean period of 7.5 years (range 1 month-26 years) with old and new antiepileptic drugs as mono or add-on therapy. In 16 patients on topiramate or lamotrigine and in 11 on ketogenic diet, plasma free carnitine was prospectively evaluated before starting treatment and after 3 and 12 months, respectively. Overall, low plasma levels of free carnitine were found in 41 patients (25%); by single subgroups, 32 out of 84 patients (38%) taking valproic acid and 13 of 54 (24%) on carbamazepine, both as monotherapy or in combination, showed low free carnitine levels. A higher though not statistically significant risk of hypocarnitinemia resulted to be linked to polytherapy (31.5%) versus monotherapy (17.3%) (P=.0573). Female sex, psychomotor or mental retardation and abnormal neurological examination appeared to be significantly related with hypocarnitinemia, as well. As to monotherapy, valproic acid was associated with a higher risk of hypocarnitinemia (27.3%) compared with carbamazepine group (14.3%). Neither one of the patients on topiramate (10), lamotrigine (5) or ketogenic diet (11) developed hypocarnitinemia during the first 12 months of treatment. Carnitine deficiency is not uncommon among epilepsy children and adolescents and is mainly linked to valproate therapy; further studies are needed to better understand the clinical significance of serum carnitine decline.

Temporal lobe tumoral epilepsy: characteristics and predictors of surgical outcome

OBJECTIVE

To review the clinical and neurophysiologic features and surgical outcome in patients with intractable temporal lobe tumoral epilepsy.

METHODS

Patients with intractable temporal lobe epilepsy who underwent resection of temporal lobe tumors, confirmed by surgical pathology, seen between 1985 and 2000 at Yale University School of Medicine Epilepsy Center, were selected. Medical records were reviewed for age at diagnosis, age at onset of seizures, delay between seizure onset and tumor diagnosis, types and frequencies of seizures, EEG results, use of anticonvulsants, extent of surgery, and pathologic diagnosis.

RESULTS

Sixty-eight patients were identified, 94.1% of them with low-grade tumors. Complex partial seizure was the most common seizure type. All patients underwent at least one surgical procedure with average follow-up of 9 years after surgical intervention. Eighty-seven percent of patients had significant postoperative seizure improvement (Engel's classes I and II). Gross total tumor resection predicted postoperative seizure freedom (p = 0.002), whereas patients with early surgical intervention, auras, and simple partial seizures had a tendency toward better seizure outcome.

CONCLUSIONS

Long-term follow-up of patients with intractable temporal lobe tumoral epilepsy suggests good response of seizures to surgery, which is unrelated to age at diagnosis, EEG, or pathology. Extent of tumor resection was significantly predictive of outcome, whereas early intervention and presence of simple partial seizures showed trends as predictive factors.

Hypouricemia in severely disabled children: influence of valproic acid and bed-ridden state

Although hypouricemia does not directly elicit clinical symptoms, it is a sensitive indicator for detecting renal tubular involvement. To determine the influence of valproic acid (VPA) and a non-ambulatory state on the serum uric acid level in epileptic children, we performed a cross-sectional study of laboratory data including serum and urinary uric acid levels and renal tubular function levels in epileptic children. We studied 93 patients in our outpatient clinic. They were divided into four groups according to two factors; VPA administration and the ambulatory state: non-ambulatory patients taking VPA (24 cases), non-ambulatory patients not taking VPA (18 cases), ambulatory patients taking VPA (29 cases), and ambulatory patients not taking VPA (22 cases). The laboratory data including uric acid levels and renal tubular function in each group were analyzed statistically using analysis of variance. Both VPA (P<0.05) and a non-ambulatory state (P<0.01) significantly decreased the serum uric acid levels with its increased urinary excretion of uric acid. However, in ambulatory patients, the uric acid level was not decreased. Serum uric acid levels was significantly decreased in non-ambulatory, severely disabled children treated with VPA. It should be borne in mind that VPA-induced renal tubular dysfunction may be present in severely disabled children. However, further investigation is necessary to determine the factor in severely disabled children that causes hypouricemia

Pharmacological and therapeutic properties of valproate: a summary after 35 years of clinical experience

Thirty-five years since its introduction into clinical use, valproate (valproic acid) has become the most widely prescribed antiepileptic drug (AED) worldwide. Its pharmacological effects involve a variety of mechanisms, including increased gamma-aminobutyric acid (GABA)-ergic transmission, reduced release and/or effects of excitatory amino acids, blockade of voltage-gated sodium channels and modulation of dopaminergic and serotoninergic transmission. Valproate is available in different dosage forms for parenteral and oral use. All available oral formulations are almost completely bioavailable, but they differ in dissolution characteristics and absorption rates. In particular, sustained-release formulations are available that minimise fluctuations in serum drug concentrations during a dosing interval and can therefore be given once or twice daily. Valproic acid is about 90% bound to plasma proteins, and the degree of binding decreases with increasing drug concentration within the clinically occurring range. Valproic acid is extensively metabolised by microsomal glucuronide conjugation, mitochondrial beta-oxidation and cytochrome P450-dependent omega-, (omega-1)- and (omega-2)-oxidation. The elimination half-life is in the order of 9 to 18 hours, but shorter values (5 to 12 hours) are observed in patients comedicated with enzyme-inducing agents such as phenytoin, carbamazepine and barbiturates. Valproate itself is devoid of enzyme-inducing properties, but it has the potential of inhibiting drug metabolism and can increase by this mechanism the plasma concentrations of certain coadministered drugs, including phenobarbital (phenobarbitone), lamotrigine and zidovudine. Valproate is a broad spectrum AED, being effective against all seizure types. In patients with newly diagnosed partial seizures (with or without secondary generalisation) and/or primarily generalised tonic-clonic seizures, the efficacy of valproate is comparable to that of phenytoin, carbamazepine and phenobarbital, although in most comparative trials the tolerability of phenobarbital was inferior to that of the other drugs. Valproate is generally regarded as a first-choice agent for most forms of idiopathic and symptomatic generalised epilepsies. Many of these syndromes are associated with multiple seizure types, including tonic-clonic, myoclonic and absence seizures, and prescription of a broad-spectrum drug such as valproate has clear advantages in this situation. A number of reports have also suggested that intravenous valproate could be of value in the treatment of convulsive and nonconvulsive status epilepticus, but further studies are required to establish in more detail the role of the drug in this indication. The most commonly reported adverse effects of valproate include gastrointestinal disturbances, tremor and bodyweight gain. Other notable adverse effects include encephalopathy symptoms (at times associated with hyperammonaemia), platelet disorders, pancreatitis, liver toxicity (with an overall incidence of 1 in 20,000, but a frequency as high as 1 in 600 or 1 in 800 in high-risk groups such as infants below 2 years of age receiving anticonvulsant polytherapy) and teratogenicity, including a 1 to 3% risk of neural tube defects. Some studies have also suggested that menstrual disorders and certain clinical, ultrasound or endocrine manifestations of reproductive system disorders, including polycystic ovary syndrome, may be more common in women treated with valproate than in those treated with other AEDs. However, the precise relevance of the latter findings remains to be evaluated in large, prospective, randomised studies.

Characterization of plasma acylcarnitines in patients under valproate monotherapy using ESI-MS/MS

OBJECTIVES

The effect of administration of the antiepileptic drug valproate (VPA), on the composition of the plasma acylcarnitine profile (including free carnitine) was investigated.

DESIGN AND METHODS

Plasma samples were obtained from 18 individuals (13 males:5 females; 15-65 y) on long-term treatment with VPA (resulting in plasma levels of 14.6-135.0 mg/L; therapeutic conc.: 40-100 mg/L). Acylcarnitines (AC) in plasma were quantified by electrospray tandem mass spectrometry (ESI-MS/MS).

RESULTS

VPA was found to increase the levels (mean +/- SD, microM) of 3-hydroxy-isovalerylcarnitine (0.10 +/- 0.04; controls: 0.02-0.06), C14:2 acylcarnitine (0.11 +/- 0.05; controls: 0.02-0.08), propylglutarylcarnitine (0.06 +/- 0.05; controls: 0.00-0.04), and C18-0H-acylcarnitine (0.09 +/- 0.05; controls: 0.00-0.04). The free carnitine (C) (42.2 +/- 9.0; controls: 22.3-54.9) and the total carnitine (52.3 +/- 10.1; controls: 26.5-73.6) were not significantly altered by VPA. Other AC (C2-C18, monounsaturated and hydroxylated) were all within the control range and especially no increase of C8 (valproyl) carnitine was observed. A positive correlation was found between the ratios [AC] / [C] (p < 0.05) or [long-chain AC (C10-C18)] / [C] (p < 0.09) with the plasma VPA concentration.

CONCLUSIONS

The unequivocal increase in 3-hydroxy-isovalerylcarnitine is consistent with the increase of 3-hydroxy-isovaleric acid observed in urine of VPA treated patients. This finding suggests an interaction mechanism of VPA with specific enzymes, namely involved in leucine metabolism. Adult patients under VPA monotherapy do not suffer from carnitine deficiency; the effect of the accumulating acylcarnitines is ill-defined.

The role of carnitine supplementation during valproic acid therapy

OBJECTIVE

To review the pathophysiology and significance of valproic acid-induced carnitine deficiency; to present and evaluate the literature pertaining to carnitine supplementation in pediatric patients receiving valproic acid; and to present the consensus guidelines for carnitine supplementation during valproic acid therapy.

DATA SOURCES

A MEDLINE search (1966-December 1998) restricted to English-language literature, using MeSH headings of carnitine and valproic acid, was conducted to identify clinically relevant articles. Selected articles and references focusing on the pediatric population were included for review.

DATA EXTRACTION

Study design, patient population, methods, and clinical outcomes were evaluated.

DATA SYNTHESIS

Valproic acid, a widely used antiepileptic agent in the pediatric population, is limited by a 1/800 incidence of fatal hepatotoxicity in children under the age of two years. Carnitine is an essential amino acid necessary in beta-oxidation of fatty acids and energy production in cellular mitochondria. It has been hypothesized that valproic acid may induce a carnitine deficiency in children and cause nonspecific symptoms of deficiency, hepatotoxicity, and hyperammonemia. Relevant published case reports and trials studying this relationship are evaluated, and a consensus statement by the Pediatric Neurology Advisory Committee is reviewed.

CONCLUSIONS

Despite the lack of prospective, randomized clinical trials documenting efficacy of carnitine supplementation in preventing valproic acid-induced hepatotoxicity, the few limited studies available have shown carnitine supplementation to result in subjective and objective improvements along with increases in carnitine serum concentrations in patients receiving valproic acid. The Pediatric Neurology Advisory Committee in 1996 provided more concrete indications on the role of carnitine in valproic acid therapy, such as valproic acid overdose and valproic acid-induced hepatotoxicity. Carnitine was strongly recommended for children at risk of developing a carnitine deficiency. Although carnitine has been well tolerated, future studies are needed to evaluate the efficacy of prophylactic carnitine supplementation for the prevention of hepatotoxicity.

L-carnitine supplementation in childhood epilepsy: current perspectives

In November 1996, a panel of pediatric neurologists met to update the consensus statement issued in 1989 by a panel of neurologists and metabolic experts on L-carnitine supplementation in childhood epilepsy. The panelists agreed that intravenous L-carnitine supplementation is clearly indicated for valproate (VPA)-induced hepatotoxicity, overdose, and other acute metabolic crises associated with carnitine deficiency. Oral supplementation is clearly indicated for the primary plasmalemmal carnitine transporter defect. The panelists concurred that oral L-carnitine supplementation is strongly suggested for the following groups as well: patients with certain secondary carnitine-deficiency syndromes, symptomatic VPA-associated hyperammonemia, multiple risk factors for VPA hepatotoxicity, or renal-associated syndromes; infants and young children taking VPA; patients with epilepsy using the ketogenic diet who have hypocarnitinemia; patients receiving dialysis; and premature infants who are receiving total parenteral nutrition. The panel recommended an oral L-carnitine dosage of 100 mg/kg/day, up to a maximum of 2 g/day. Intravenous supplementation for medical emergency situations usually exceeds this recommended dosage.

Serum carnitine levels in epileptic children before and during treatment with valproic acid, carbamazepine, and phenobarbital

Serum levels of free, acyl, and total carnitine were determined in 32 patients with seizures, before and after 3, 6, and 12 months of treatment with valproic acid (17 patients), carbamazepine (10 patients), or phenobarbital (5 patients). In all three treated groups, both free and total carnitine levels showed a significant decline with respect to pretreatment levels. This decline was most marked and most consistent in patients treated with valproic acid. In 35% of the patients in this group, carnitine deficiency (ie, total carnitine < 30 micromol/L) was observed by month 12. In none of the three groups were serum carnitine levels significantly correlated with the serum concentration of the drug. These findings suggest a need to monitor serum carnitine levels in children treated with any of these drugs.

Effect of valproate on the pharmacokinetics of free and total plasma bilirubin in experimental hyperbilirubinemia in guinea pigs

The effects of valproate (VPA) on free and total bilirubin concentrations in plasma were studied in guinea pigs. Steady-state hyperbilirubinemia (around 2.5-3.0 mg/100 mL) was induced by constant intravenous (i.v.) infusion of bilirubin followed by an i.v. bolus dose of sodium valproate (VPA-Na) of 50 (n = 4) or 200 (n = 5) mg/kg. Steady-state plasma total bilirubin concentration was lowered by 40% and 55% and the unbound fraction (fu) increased by 1.9- and 4.9-fold at the respective doses of 50 mg/kg and 200 mg/kg VPA-Na. Free bilirubin was not significantly changed by 50 mg/kg VPA-Na, but did show a significant transient elevation with the 200 mg/kg dose. In another experiment, guinea pigs (n = 3) were given a constant i.v. infusion of VPA-Na to maintain a steady-state plasma concentration (58 micrograms/mL), followed by an i.v. bolus dose of bilirubin (2 mg/kg). A control study (n = 3) was performed simultaneously using normal saline instead of VPA. Free bilirubin was detectable only following induction of hyperbilirubinemia in either group. A higher volume of distribution and lower elimination rate constant of bilirubin were observed in the VPA-treated than in the control animals. The displacement effect of VPA on bilirubin-plasma binding in vitro was studied by adding serial concentrations of VPA-Na to bilirubin-plasma solution. VPA displaced bilirubin from the high-affinity plasma protein binding site, with a binding constant (KD) of 5.7 x 10(-2)/microM. Similar displacement of bilirubin plasma protein binding was observed in vivo. These results suggest that VPA reduces plasma protein binding and slows the elimination rate of bilirubin. The principal mechanism for decreased plasma concentrations of total bilirubin by administration of VPA is caused by decreased plasma binding, as opposed to metabolic induction.

Effects of long-term administration of the antiepileptic drug--sodium valproate upon the ultrastructure of hepatocytes in rats

Chronic intragastric application (1, 3, 6, 9 and 12 months) of the antiepileptic drug--sodium valproate (VPA; Vupral "Polfa") to rats in the effective dose of 200 mg/kg b.w./day exerts hepatotoxic effect after 9 and 12 months of the experiment. The first ultrastructural changes in hepatocytes were observed after 3 months of the drug administration. These became more intense in the subsequent stages of the experiment, to be most pronounced after 12 months. The most striking changes were in the mitochondria (significant swelling, an increase in their number, degeneration of matrix and cristae, disruption of the outer mitochondrial membrane) and in peroxisomes (proliferation, enlargement and the presence of distinct nucleoids). Further alterations in hepatocytes manifested themselves in: microvesicular fatty change with cholesterolosis (cholesterol clefts), damage to the cellular membrane of the sinusoidal pole with dilation of the perisinusoidal space of Disse, presence of cystern-like cytoplasmic vacuoles in the sinusoidal region, filled with plasma-like material and focal cytoplasmic necrosis. The changes in hepatocytes coexisted with the swelling and activation of sinusoidal cells, endothelial cells and Kupffer cells. The author suggests that mitochondria and peroxisomes considerably contribute to the morphogenesis of hepatocyte damage by VPA in the chronic experimental model.

The effects of long-term anticonvulsive treatment on serum lipid profile

Serum lipids were determined in 10 untreated patients with recently diagnosed epilepsy, 21 patients treated with carbamazepine (CBZ), 10 patients treated with valproate (VPA) and in 15 healthy children. In relation to the controls, patients receiving CBZ showed increased serum high-density lipoprotein cholesterol (HDLc), apolipoprotein A (Apo-A) and apolipoprotein B (Apo-B). Patients receiving VPA showed increased Apo-B levels. There were no significant differences in total cholesterol (TC), triglycerides (TG), low-density lipoprotein cholesterol (LDLc) or very low-density lipoprotein cholesterol (VLDLc) between all groups. The changes in lipid metabolism may be associated with the induction of liver enzymes during anti-epileptic drug metabolism. The CBZ-induced change in serum lipid levels was considered to be a possible factor against atherosclerosis and coronary heart disease in epileptic patients.

Physical activity, health-related fitness, and health experience in adults with childhood-onset epilepsy: a controlled study

PURPOSE

To show any possible associations between childhood-onset epilepsy and physical activity, health-related fitness, and health experience.

METHODS

A population-based cohort of 176 patients with epilepsy since childhood was monitored for a mean of 35 years. Patients with recurrent, unprovoked epileptic seizures with no associated initial neurologic impairment or disability, termed those with "epilepsy only" (n = 100), were compared with matched controls for self-reported physical activity, health experience, laboratory tests, body mass index, and muscle power tests.

RESULTS

On the basis of muscle tests, physical fitness proved to be significantly poorer in patients with "epilepsy only" than in matched controls. During the preceding year, 22% of patients and 24% of controls had reduced their physical activities because of some illness; only 2% reduced their physical activities because of epilepsy. No significant difference was found in blood status, except for a lower serum creatinine level in the patients. Current antiepileptic drug (AED) therapy appeared significantly associated with lower hemoglobin and creatinine levels and higher high-density lipoprotein values. The patients perceived their health status to be comparable with that of controls, irrespective of physical inactivity, continued seizures, or AED monotherapy. However, patients receiving AED polytherapy perceived their health as rather poor or very poor significantly more often than did controls.

CONCLUSIONS

Based on objective muscle tests, adults with childhood-onset "epilepsy only" have poorer physical fitness than do matched controls, but they have a feeling of good personal health.

The effect of carnitine supplementation in valproate-induced hyperammonaemia

The aim of the study was to investigate the effect of carnitine supplementation of valproic acid (VPA) treated patients presenting with increased plasma ammonia concentrations. Plasma ammonia concentrations were recorded in 69 children and young adults on VPA monotherapy (25.6 +/- 9.2 mg VPA/kg per day; mean plasma VPA concentration 68.8 +/- 27.6 mg/l). Their mean plasma ammonia concentration was 80.2 +/- 32.1 micrograms/dl (median 73.1 microgram/dl). A total of 24 patients (35.3%) presenting with ammonia concentrations > 80 microgram/dl were considered hyperammonaemic. Of these, 15/24 (22.1%) showed ammonia concentrations > 100 microgram/dl, even up to 194 micrograms/dl. In 48/69 patients, plasma carnitine concentrations could be determined. The plasma total carnitine (TC) concentrations were rather low (26.9 +/- 8.8 mumol/1) compared to normal values obtained in our laboratory (40.9 +/- 7.2 mumol/1). The percentage of free carnitine was considered decreased (< 75% TC) in 13/48 samples (27%). Fourteen hyperammonaemic patients and one with a plasma ammonia level of 60 micrograms/dl agreed to be supplemented with L-carnitine (1 g/m2 per day divided into two equal doses). Their plasma ammonia and carnitine concentrations were re-evaluated after a mean of 9.1 +/- 4.0 days (median 9.0 days) and in 9 patients again after a mean of 79.6 +/- 30.1 days (median 75 days) of L-carnitine supplementation. Plasma ammonia concentrations decreased in all 15 patients. The decrease was 25.4 +/- 11.2% (median 28.3%) after a mean of 9.1 +/- 4.0 days and amounted to 46.0 +/- 17.2% (median 48%) after 79.6 +/- 30.1 days. L-Carnitine supplementation led to an increase in plasma free carnitine of 11.6 +/- 13.0% (median 15.6%) and to a further increase of 11.1 +/- 8.4% (median 11.5%) when re-evaluated a second time. The plasma ammonia concentrations were significantly correlated with the percentage of free plasma carnitine (r = -0.67; p < 0.0001). The results show that carnitine supplementation is a means of normalizing elevated plasma ammonia concentrations. However, we cannot conclude from our results whether this lowers the risk of developing a VPA-induced Reye's-like syndrome.

Reduced carnitine and antiepileptic drugs: cause relationship or co-existence?

Serum carnitine was measured longitudinally before and after therapy in 15 patients receiving valproic acid, 14 patients receiving carbamazepine and 8 patients receiving phenobarbital. The patients who received valproic acid showed a significant reduction in free (and total) serum carnitine (mean (SE) 37.6 (6.2) mumol/l without valproic acid, 29.1 (1.6) mumol/l with valproic acid (p < 0.001)). Such an effect was not found in patients receiving carbamazepine or phenobarbital.

Heterozygotes for plasmalemmal carnitine transporter defect are at increased risk for valproic acid-associated impairment of carnitine uptake in cultured human skin fibroblasts

One of the mechanisms by which chronic valproic acid (VPA) therapy induces serum and tissue depletion of carnitine in normal controls is through inhibition of plasmalemmal carnitine uptake (Tein et al 1993). To determine the effect of VPA on proven heterozygotes for the plasmalemmal carnitine transporter defect, we studied this system in cultured human skin fibroblasts with reduced Vmax for the carnitine transporter using L-[3H]carnitine. There was en exponential dose-dependent decrease in carnitine uptake with increasing VPA concentrations and the relative inhibitory effect was the same for all three carnitine concentrations for a given cell line. Importantly, the lower the maximal velocity of carnitine uptake of the heterozygote, the lower the number of carnitine transporters and the lower the carnitine uptake per given concentration of VPA. The degree of inhibition was also directly proportional to the time of VPA preincubation up to a specific maximal saturation time. The maximal effect of VPA exposure time was reached by 10 days in the control cell line and by 3 days in the two heterozygote lines, probably reflecting earlier saturation. We conclude that patients who are heterozygous for the plasmalemmal carnitine transporter defect are at increased risk for VPA-associated serum and tissue depletion of carnitine through inhibition of plasmalemmal carnitine uptake.

Plasma amino acid alterations in idiopathic generalized epilepsy: an investigation in probands and their first-degree relatives

Twenty-two plasma amino acids were determined by means of ion-exchange chromatography in 16 previously untreated patients with generalized idiopathic epilepsy and in some of their first-degree relatives (26 subjects), and the results were compared with those obtained from a group of 50 healthy controls. The patients were subsequently treated with valproic acid for one month and then reexamined. In the epileptic subjects, statistical analysis showed significant alterations in the plasma levels of a group of amino acids, including the four associated with neuro-transmission (aspartate, glutamate, glycine, taurine); aspartate, glutamate and glycine levels were also altered in the first-degree relatives. Valproic acid therapy did not affect amino acid levels. If further confirmed, these alterations might be considered possible neurochemical markers of epilepsy.

Therapeutic drug monitoring in pediatrics: a need for improvement

Therapeutic drug monitoring (TDM) is practiced for a number of frequently used drugs in infants and children. It is believed that monitoring drug levels will increase the probability of a therapeutic response and minimize the probability of adverse drug sequelae. Dose adjustments are based on measured drug levels interpreted relative to published therapeutic ranges which may or may not reflect the true relationship with either therapeutic or adverse effects. Potential errors derive from many sources, some amenable to solutions based on current knowledge, others awaiting improved understanding of the causes and consequences of unreliable therapeutic ranges.

Effects of valproate and E-2-en-valproate on functional and morphological parameters of rat liver. III. Influence of fasting

Valproate (VPA) therapy has been associated with a rare but fatal hepatotoxicity. Several possible biochemical mechanisms responsible for the hepatotoxicity have been proposed, but the matter has not been decided. There is some evidence that VPA-associated hepatotoxicity may represent the consequences of a VPA overload on a limited mitochondrial beta-oxidation capacity, causing abnormalities in metabolic pathways. If this assumption is true, fasting-induced increase of endogenous fatty acids, which compete with VPA for beta-oxidation, should enhance the hepatotoxic potential of VPA. Indeed, involuntary fasting because of anorexia, e.g., in children with febrile infections, has been discussed as one clinical risk pattern preceding VPA-associated hepatic fatalities. In the present experiments, the effects of fasting on functional and morphological parameters of the liver were studied in young male rats chronically treated with VPA. E-2-en-VPA (trans-2-en-VPA), a major active metabolite of the beta-oxidation pathway of VPA, was used for comparison. Both drugs were administered at doses of 250 mg/kg i.p. 3 times daily for 1 week. In control rats, a 40-h fasting period resulted in marked mobilization of liver lipid and glycogen stores, alterations in liver enzyme activities, and hyperammonemia. In rats treated with VPA, fasting reduced beta-oxidation of the drug, but seemed not to increase its hepatotoxic potential. Compared to experiments without fasting, alterations in liver enzymes and ammonia levels induced by VPA were less marked or absent in fasted rats, and histopathological examination of liver sections did not indicate degenerative liver lesions in response to drug treatment. Thus, compared to previous rat studies on VPA without fasting, fasting appeared to attenuate VPA's hepatotoxic potency, possibly as a result of fasting-induced increases in carnitine levels. In rats treated with E-2-en-VPA, no indication of hepatotoxicity was evident, and alterations in functional hepatic parameters were less pronounced than with VPA. The data do not indicate that fasting or poor nutrition are risk factors for VPA-associated hepatic injury.

Valproate and palmitate binding to serum albumin in valproate-treated patients. Relation to obesity

Binding of valproate and palmitate to serum albumin was studied in 29 valproate-treated epileptic patients. The results were compared with similar observations in a reference group of 43 non valproate-treated individuals. The binding affinity for palmitate was decreased (P < 0.0001) resulting in increased availability of long-chain fatty acids (P = 0.008) due to competitive valproate binding in the valproate-treated patients. The findings support a hypothesis on the pathogenesis of obesity as a complication of valproate treatment of epilepsy.

Carnitine disposition before and during valproate therapy in patients with epilepsy

Free and total carnitine and acylcarnitine in plasma and urine samples was measured in 22 epileptic patients before and after 15 and 45 days of valproate (VPA) therapy and in 16 healthy volunteers on a single occasion. Carnitine plasma concentration and renal excretion observed in epileptic patients before VPA therapy did not differ from control values. After VPA was started, free and total plasma concentration decreased significantly (p < 0.05) from 49 +/- 17 to 35 +/- 16 at 15 days and to 35 +/- 13 nmol/ml at 45 days of therapy (free carnitine) and from 60 +/- 18 to 50 +/- 18 at 15 days and to 55 +/- 14 nmol/ml at 45 days of therapy (total carnitine), whereas acylcarnitine increased significantly (p < 0.05) from 10 +/- 8 to 14 +/- 8 at 15 days and to 18 +/- 16 nmol/ml at 45 days of therapy. Free carnitine urinary excretion decreased significantly (p < 0.05) from 200 +/- 135 to 115 +/- 76 and 118 +/- 75 mumol/24 h, whereas acylcarnitine urinary excretion increased significantly (p < 0.05) from 78 +/- 56 to 154 +/- 98 and 155 +/- 89 mumol/24 h after VPA therapy was started. As a consequence, acylcarnitine renal clearance increased significantly (+30%, p < 0.05) whereas free carnitine renal clearance did not change during VPA therapy. No difference was detected between 15 and 45 days of therapy. No patients experienced symptoms of VPA toxicity. Our results suggest that VPA in patients increases both formation and renal clearance of acylcarnitine.

Valproate hepatotoxicity syndrome: hypotheses of pathogenesis

Therapeutic use of the anticonvulsant valproate (VPA) has been associated with a rare, but severe and often fatal hepatotoxicity. Cases usually present with lethargy, anorexia, and vomiting with rapid progression to coma. Liver histopathology is characterized by steatosis with and without necrosis. In some instances only necrosis was present. Several hypotheses of pathogenesis have been postulated. These deal mainly with biochemical systems that are known to be affected by VPA, or with the possible idiosyncratic production of toxic VPA metabolites, especially delta 4-VPA. At present, no hypothesis entirely explains the diverse characteristics of the disorder.

Reduction of serum carnitine concentrations during anticonvulsant therapy with phenobarbital, valproic acid, phenytoin, and carbamazepine in children

We determined four carnitine constituents (total and free carnitine and short- and long-chain fatty acid carnitine esters) in serum from 471 patients treated for convulsions with phenobarbital, valproic acid, phenytoin, and/or carbamazepine. The 471 patients were in eight treatment groups; four were treated with monotherapy and four with polytherapy. The means of all four carnitine constituents were significantly reduced in all treatment groups (except for free carnitine in four groups). Total carnitine was reduced by 23% to 48%, free carnitine by 9% to 45%, short-chain fatty acid carnitine by 46% to 64%, and long-chain fatty acid carnitine by 6% to 29%. Patient frequency of reduction for total carnitine was 20% of all patients (10% for free carnitine), 23% of patients receiving valproate (9% for free carnitine), 36% of those receiving phenobarbital (21% for free carnitine), 12% of those receiving phenytoin (8% for free carnitine), and 8% of those receiving carbamazepine (1% for free carnitine). Only for phenobarbital was there an inverse correlation between the serum concentration of the drug and that of carnitine concentration. One patient receiving carbamazepine had a 59% reduction in the total and a 65% reduction in the free carnitine concentration and a fivefold increase in long-chain fatty acid carnitine, values similar to those seen in neonatal lethal carnitine palmitoyl transferase II deficiency. It remains to be determined whether a reduction in serum carnitine values in patients receiving anticonvulsant therapy is of clinical consequence, whether the reduction is present in some patients before the start of therapy, when and by what mechanism carnitine levels may become reduced during therapy, and whether the reduction exists in the solid tissues of these patients.

Effects of acute valproic acid administration on carnitine plasma concentrations in epileptic patients

Serial plasma samples collected after an acute administration of valproic acid, (VPA, 15 mg/kg as oral solution) in epileptic patients were selected for this study. The plasma samples were selected from three different groups of patients; patients on phenobarbital and phenytoin with clinical VPA intolerance (group A); patients on phenobarbital and phenytoin without clinical VPA toxicity (group B); and patients without phenobarbital and phenytoin and without clinical VPA toxicity (group C). Plasma samples from 6 patients per group were analyzed for carnitines and ammonia. Ammonia levels during acute study increased significantly (P less than 0.05) in patients who experienced VPA intolerance, while no changes were found in the other patients. After acute VPA administration, total carnitine was unchanged but free carnitine was decreased (P less than 0.05) and carnitine esters were increased (P less than 0.05) in all groups of patients studied. No difference in carnitine profiles was seen between patients with or without evidence of VPA administration has an important effect on carnitine metabolism. However, unlike the acute effect on ammonia metabolism, this acute effect does not seem to be correlated with any associated antiepileptic therapy, nor does it predict clinical VPA intolerance.

Carnitine, valproate, and toxicity

Carnitine is an important nutrient that is present in the diet (particularly in meat and dairy products) and is synthesized from dietary amino acids. It functions to assist long-chain fatty acid metabolism and to regulate the ratio of free coenzyme A to acylcoenzyme A in the mitochondrion. Carnitine deficiency occurs in primary inborn errors of metabolism, in nutritional deficiency, and in various other disorders including antiepileptic drug therapy. Valproate therapy is often associated with decreased carnitine levels and occasionally with true carnitine deficiency. Some experimental and clinical evidence links valproate-induced carnitine deficiency with hepatotoxicity, but this evidence is limited and inconclusive. Carnitine supplementation has been useful in some studies, but these data are also limited. Young children with neurologic disabilities taking multiple antiepileptic drugs may have the greatest risk for carnitine deficiency. Measurement of carnitine levels appears warranted in these patients and in patients with symptoms and signs of possible carnitine deficiency.