Carnitine deficiency associated with anticonvulsant therapy

Rational analysis of data from LC-MS/MS: new insights in acylcarnitines as biomarkers for brain disorders or neurotoxicity

Objective

LC-MS/MS-based metabolomics is an important tool for studying disease-related biomarkers. Conventionally, different strategies have been used to screen biomarkers. However, many studies for biomarker screening by different strategies have ignored the dose-response relationship between the biomarker level and exposure level, and no relevant studies have described and compared different strategies in detail. Phenobarbital (PHB) which belongs to the barbiturates, was selected as the typical representative of neurotoxins. Acylcarnitines have been promising candidates for diagnostic biomarkers for several neurological disorders and neurotoxicity. In this work, we aimed to use an acute PHB poisoning animal model to clarify PHB poisoning effects on plasma and brain acylcarnitine changes and how to rationally analyze data from LC-MS/MS.

Methods

The acylcarnitine profiles in plasma and brain regions in an actuate PHB poisoning animal model were utilized. The dose-response relationship between plasma PHB and carnitine and acylcarnitines (CARs) in plasma and brain were assessed by the variance analysis trend test and Spearman's rank correlation test. In different strategies, principal component analysis (PCA) and partial least squares discriminant analysis (OPLS-DA) screened the differential CARs, variable importance plots (VIPs) were utilized to select putative biomarkers for PHB-induced toxicity, and receiver operating characteristic (ROC) curve analysis then illustrated the reliability of biomarkers.

Results

Under the first strategy, 14 potential toxicity biomarkers were obtained including eight downregulated CARs with AUC >0.8. Under the second strategy, 11 potential toxicity biomarkers were obtained containing five downregulated CARs with AUC >0.8. Only when the dose-response relationship was fully considered, different strategies screen for the same biomarkers (plasma acetyl-carnitine (C2) and plasma decanoyl-carnitine (C10)), which indicated plasma acylcarnitines might serve as toxicity biomarkers. In addition, the plasma CAR level changes showed differences from brain CAR level changes, and correlations between plasma CARs and their brain counterparts were weak.

Conclusion

We found that plasma C2 and C10 might serve as toxicity biomarkers for PHB poisoning disorders, and PHB poisoning effects on changes in plasma CARs may not be fully representative of changes in brain CARs.

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.

Factors associated with blood carnitine levels in adult epilepsy patients with chronic valproic acid therapy

AIMS

Valproic acid (VPA) is a widely used antiepileptic drug for the treatment of epilepsy, seizures, and bipolar and psychiatric disorders. A deficiency of carnitine, a compound involved in energy production, is associated with chronic VPA use. However, the clinical factors affecting blood carnitine levels and their pathophysiology remain unclear. Hence, we aimed to identify the factors that correlated with serum carnitine levels in epilepsy patients receiving chronic VPA therapy.

METHODS

This observational study included 138 epilepsy patients receiving chronic VPA therapy. Serum total and free carnitine levels, routine blood tests and drug concentrations were assessed. The correlation between carnitine levels and other factors were calculated using Spearman's rank correlation coefficients, and a principal component analysis (PCA) and a multiple linear regression analysis were performed.

RESULTS

Overall, serum free carnitine levels showed significant negative correlations with epilepsy duration, VPA treatment duration, daily VPA dose, and blood VPA concentration. A significant positive correlation was observed with erythrocyte count, hemoglobin levels, and creatinine levels. Of the 138 patients, 21 (15.2 %) with serum free carnitine levels of <20 μmol/L had significantly longer disease duration, a higher daily VPA dose, and lower blood clobazam concentrations. In the 48 VPA monotherapy patients, serum free carnitine levels showed a significant negative correlation with disease duration and duration of VPA therapy. Furthermore, in the 2.1 % patients receiving VPA monotherapy, serum free carnitine levels were <20 μmol/L. PCA resulted in seven factor solution (eigenvalue >1; 71.67 % explained variance). Component 1 clearly revealed the maximal loading for serum free carnitine level (.792) and the most negative loading for disease duration of epilepsy (-.595). A linear regression analysis revealed that the duration of epilepsy, serum creatinine level, and daily dose of VPA were significant (p < .01) factors that affected serum free carnitine levels.

CONCLUSIONS

The effects of combination therapy with VPA and other anti-epileptic drug(s) on carnitine levels are higher than that of VPA monotherapy. Additionally, epilepsy duration may affect serum free carnitine level.

[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.

Assessment of Subclinical Pancreatitis in Epileptic Children With Different Treatment Modalities

Acute pancreatitis differ in pediatrics and adults. Drug-induced pancreatitis is one of the common causes of pancreatitis in children. This case–control study aimed to assess subclinical pancreatitis in patients with epilepsy treated with different drug regimens. Eighty known patients with epilepsy were enrolled. Forty patients were treated with monotherapy (group I) and 40 were treated with multitherapy (group II) regimens. Twenty age- and sex-matched healthy children were enrolled as control (group III). Serum lipase and amylase were assayed in all included children. Significant differences were found between groups I and III and between groups II and III regarding serum amylase and lipase (P < .001 for all). Significant difference were found between groups I and II (P = .024) and between groups II and III (P = .01) regarding pancreatic duct and body diameters. Significant difference were found between patients with controlled and uncontrolled fits regarding serum amylase (P = .008). In conclusion, subclinical pancreatitis can complicate the treatment with different antiepileptic regimens.

Levocarnitine and Dialysis: A Review

Among the various metabolic abnormalities documented in dialysis patients are abnormalities related to the metabolism of fatty acids. Aberrant fatty-acid metabolism has been associated with the promotion of free-radical production, insulin resistance, and cellular apoptosis. These processes have been identified as important contributors to the morbidity experienced by dialysis patients. There is evidence that levocarnitine supplementation can modify the deleterious effects of defective fatty-acid metabolism. Patients receiving hemodialysis and, to a lesser degree, peritoneal dialysis have been shown to be carnitine deficient, as manifested by reduced levels of plasma free carnitine and an increase in the acyl:free carnitine ratio. Cardiac and skeletal muscles are particularly dependent on fatty-acid metabolism for the generation of energy. A number of clinical abnormalities have been correlated with a low plasma carnitine status in dialysis patients. Clinical trials have examined the efficacy of levocarnitine therapy in a number of conditions common in dialysis patients, including skeletal-muscle weakness and fatigue, cardiomyopathy, dialysis-related hypotension, hyperlipidemia, and anemia poorly responsive to recombinant human erythropoietin therapy (rHuEPO). This review examines the evidence for carnitine deficiency in patients requiring dialysis, and documents the results of relevant clinical trials of levocarnitine therapy in this population. Consensus recommendations by expert panels are summarized and contrasted with present guidelines for access to levocarnitine therapy by dialysis patients.

Effects of Valproate on Acylcarnitines in Children with Epilepsy Using ESI-MS/MS

PURPOSE

To determine the influence of valproate (VPA) treatment on acylcarnitines in children with epilepsy.

METHODS

Determination of acylcarnitines (including free carnitine and acylcarnitines from C2 to C18) in dried blood spot specimens using tandem-mass spectrometry. Longitudinal study of changes in acylcarnitines in children under VPA treatment without pretreatment (group 1) or with pretreatment with other antiepileptic drugs (group 2) before the start of VPA treatment at an early and a late treatment interval (12-66, 90-260 days after the beginning of treatment, respectively). Cross-sectional comparison of these two VPA groups and of a group receiving carbamazepine monotherapy (group 3) with controls.

RESULTS

Acylcarnitines in epileptic patients before VPA therapy did not differ from control values. In group 1, decreases of C0 (-26%), C2 (-12%), C16 (-31%), C18 (-41%), C(total) (-10%), increases of C5OH (+31%), C8 (+33%) in the early treatment interval, and decreases of C16 (-21%), C18 (-42%), and increases of C2 (+26%), C5OH (+44%) in the late treatment interval were significant. In group 2, both in the longitudinal and the cross-sectional study, only a decrease of C18 (-41%, -43%, respectively) in the late treatment interval was found. In group 3, no significant changes have been observed.

CONCLUSIONS

We could prove changes in acylcarnitine subspecies, which were associated with VPA treatment in children with epilepsy. The treatment interval with the most marked changes coincides with the interval of highest risk for VPA-induced hepatotoxicity. The observed specific acylcarnitine pattern might point to the impaired intermediary metabolism that is responsible for VPA-induced hepatotoxicity.

Interaction between Anticonvulsants and Human Placental Carnitine Transporter

PURPOSE

To examine the inhibitory effect of anticonvulsants (AEDs) on carnitine transport by the human placental carnitine transporter.

METHODS

Uptake of radiolabeled carnitine by human placental brush-border membrane vesicles was measured in the absence and presence of tiagabine (TGB), vigabatrin (VGB), gabapentin (GBP), lamotrigine (LTG), topiramate (TPM), valproic acid (VPA), and phenytoin (PHT). The mechanism of the inhibitory action of TGB was determined.

RESULTS

Most of the AEDs inhibited placental carnitine transport. Kinetic analyses showed that TGB had the greatest inhibitory effect [50% inhibitory concentration (IC50, 190 microM)], and the order of inhibitory potency was TGB > PHT > GBP > VPA > VGB, TPM > LTG. Further studies showed that TGB competitively inhibited carnitine uptake by the human placental carnitine transporter, suggesting that it may be a substrate for this carrier.

CONCLUSIONS

Although the involvement of carnitine deficiency in fetal anticonvulsant syndrome requires further evaluation, potential interference with placental carnitine transport by several AEDs was demonstrated. Despite the higher inhibitory potency of TGB, given the therapeutic unbound concentrations, the results for VPA and PHT are probably more clinically significant.

Carnitine transport: pathophysiology and metabolism of known molecular defects

Early-onset dilatative and/or hypertrophic cardiomyopathy with episodic hypoglycaemic coma and very low serum and tissue concentrations of carnitine should alert the clinician to the probability of the plasmalemmal high-affinity carnitine transporter defect. The diagnosis can be established by demonstration of impaired carnitine uptake in cultured skin fibroblasts or lymphoblasts and confirmed by mutation analysis of the human OCTN2 gene in the affected child and obligate heterozygote parents. The institution of high-dose oral carnitine supplementation reverses the pathology in this otherwise lethal autosomal recessive disease of childhood, and carnitine therapy from birth in prospectively screened siblings may altogether prevent the development of the clinical phenotype. Heterozygotes may be at risk for cardiomyopathy in later adult life, particularly in the presence of additional risk factors such as hypertension and competitive pharmacological agents. OCTN2 belongs to a family of organic cation/carnitine transporters that function primarily in the elimination of cationic drugs and other xenobiotics in kidney, intestine, liver and placenta. The high- and low-affinity human carnitine transporters, OCTN2 and OCTN1, are multifunctional polyspecific organic cation transporters; therefore, defects in these transporters may have widespread implications for the absorption and/or elimination of a number of key pharmacological agents such as cephalosporins, verapamil, quinidine and valproic acid. A third organic/cation carnitine transporter with high specificity for carnitine, Octn3, has been cloned in mice. The juvenile visceral steatosis (jvs) mouse serves as an excellent clinical, biochemical and molecular model for the high-affinity carnitine transporter OCTN2 defect and is due to a spontaneous point mutation in the murine Octn2 gene on mouse chromosome 11, which is syntenic to the human locus at 5q31 that harbours the human OCTN2 gene.

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.

Effect of long-term valproic acid administration on the efficiency of carnitine reabsorption in humans

To elucidate the etiology of valproic acid-induced carnitine deficiency, we tested the hypothesis that long-term valproic acid administration decreases the rate of carnitine reabsorption. Thirteen healthy men participated in a 34-day protocol in which carnitine clearance was measured before and after 28 days of valproic acid administration. During valproic acid administration (days 6 to 33), plasma free and total carnitine concentrations decreased (18% and 12%, respectively, P<.05) by 16 days, but returned to pretreatment concentrations by 28 days. From day 14 to day 30, the rate of free carnitine excretion was 50% lower than at baseline (day 4, P<.05). Free and total carnitine clearance, indexed to the glomerular filtration rate, was lower after valproic acid administration (P<.01). Contrary to our hypothesis, after 28 days of valproic acid administration, the rate of carnitine reabsorption was enhanced independent of the glomerular filtration rate and filtered load. Changes in the plasma concentration, rate of excretion, and clearance were specific for carnitine and were not generalized in magnitude or direction to the other amino acids. We conclude that the kidney adapts to conserve carnitine during valproic acid administration and therefore does not cause valproic acid-induced carnitine depletion in adults.

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.

Hatred of the hemiparetic limbs (misoplegia) in a 10 year old child

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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.

Early childhood hepatocerebral degeneration misdiagnosed as valproate hepatotoxicity

Four unrelated children were thought to have valproate-associated hepatotoxicity. They presented with recurrent partial secondarily generalized status epilepticus and epilepsia partialis continua followed by mental and motor regression. Despite treatment with multiple antiepileptic medications, they continued to have seizures. After initiation of valproic acid (VPA), all 4 manifested liver failure within 3 months. Two of these children each had 1 sibling who was not exposed to VPA, but who developed the same clinical picture including liver failure. At the time of autopsy, all 6 children had similar neuropathological findings with focal areas of spongiosis and neuronal loss, diffuse gliosis, and Alzheimer type II cells. One VPA-treated patient underwent a successful liver transplantation only to die from relentlessly progressive neurological deterioration. We propose that many of the reported patients with VPA-associated hepatotoxicity represent undiagnosed patients with early childhood hepatocerebral degeneration, the Huttenlocher variant of Alpers' syndrome. This disease manifests by obstinate partial seizures, recurrent partial secondarily generalized status epilepticus, epilepsia partialis continua, psychomotor deterioration, and hepatic dysfunction that is exacerbated by VPA administration. The accelerated demise from liver failure in the nontransplanted patients before the central nervous system pathology fully evolves makes the diagnosis of this rare condition difficult. The occurrence of disease in the unexposed siblings suggests recessive inheritance.

A child with valproic acid-associated carnitine deficiency and carnitine-responsive cardiac dysfunction

Valproic acid enhances renal losses of carnitine esters and leads to decreased plasma free carnitine concentrations in many patients receiving valproic acid therapy. However, decreased serum carnitine levels are of unclear pathologic significance, and most children manifest no symptoms of carnitine deficiency. We report a child with valproic acid-associated carnitine deficiency who had severe cardiac dysfunction develop that resolved with carnitine replacement therapy.

Carbamyl phosphate synthetase-1 deficiency discovered after valproic acid-induced coma

Valproic acid induced coma is presented in an adult patient without a history of metabolic disease. Liver biopsy revealed a reduction in activity of carbamyl phosphate synthetase-I, an enzyme obligated for transformation of ammonia to urea in the urea cycle. After recovery CT scan follow-up showed marked cerebral atrophy which did not exist prior to the state of coma. Risk factors are discussed.

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.

Short-term effects of administration of anticonvulsant drugs on free carnitine and acylcarnitine in mouse serum and tissues

1. The short-term evolution of concentrations of free carnitine and acylcarnitine was studied in the serum, liver, kidney, heart and skeletal muscle of mice after administration of single therapeutic doses of the anticonvulsant drugs, valproic acid (VPA), carbamazepine (CBZ), phenytoin (PHT) and phenobarbitone (PHB). 2. The effects of the drugs were immediate but transitory, control levels of free carnitine and acylcarnitine having been recovered or almost recovered in serum and in all tissues 8 h post administration (p.a.). 3. VPA was the only drug that significantly reduced free carnitine concentration in serum, which recovered control levels by 4 h p.a. 4. All the drugs studied brought about marked deficits of serum acylcarnitine, which had disappeared 2 h p.a. in the case of VPA and not until 8 h p.a. for CBZ, PHT or PHB. 5. The minimum concentrations of free carnitine and acylcarnitine in serum were invariably associated with the maximum concentration of drug in serum. 6. Free carnitine concentration was not affected by VPA in any tissue, PHT and PHB brought about significant deficits in heart and kidney, and CBZ a significant deficit in muscle. 7. Acylcarnitine concentration was significantly reduced in heart, kidney and muscle by CBZ, PHT and PHB, but in liver the effects of all drugs were very small. 8. These results are compatible with the hypothesis that the primary cause of anticonvulsant-induced alteration of carnitine metabolism is interference with renal reabsorption of carnitine.

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.

Effects of acute valproate administration on carnitine metabolism in mouse serum and tissues

Carnitine concentrations in serum, liver, kidney, muscle and heart were determined 30 min, 2 hr and 4 hr after administration of single 50 mg/kg doses of valproic acid (VPA) or octanoic acid (OTA) of fasting mice. Half an hour post-administration (p.a.) of VPA, free carnitine concentrations were smaller than in controls in serum, liver, kidney and heart. Four hr p.a., the effects of VPA had disappeared from all the carnitine sources, which now had concentrations that were not significantly different from those of controls. The effects of OTA are different from, and sometimes the opposite of, those of VPA, showing that the effects of VPA are specific to it. Hyperammonemia, on the other hand, was greatest 4 hr p.a. of VPA. These findings show that the effect of VPA on carnitine metabolism is immediate but transient, and accordingly suggest that the carnitine deficiency observed in patients under prolonged treatment with VPA-containing anticonvulsants must be due to a more complex mechanism than direct interaction between carnitine and VPA.