Increase of valproate-induced hyperammonemia in normal subjects by carbohydrate intake

Risk factors for hyperammonemia associated with valproic acid therapy in adult epilepsy patients

Hyperammonemia is one of the side effects of treatment with valproic acid (VPA), but the risk factors and mechanisms involved remain obscure. This study analyzed the risk factors for hyperammonemia associated with VPA therapy in adult epilepsy patients. A retrospective analysis of 2724 Japanese patients (1217 males and 1507 females aged from 16 to 76years) treated with VPA between January 2006 and December 2010 were analyzed. The ammonia level increased markedly in a VPA dose-dependent manner, and was significantly elevated in patients who also used hepatic enzyme inducers such as phenytoin (PHT), phenobarbital (PB), carbamazepine (CBZ), and combinations of these drugs. When a blood ammonia level exceeding 200μg/dl was defined as hyperammonemia, the risk factors for hyperammonemia according to multiple regression analysis were a VPA dose >20mg/kg/day (odds ratio (OR): 4.1; 95% confidence interval (CI): 1.6-10.8) and concomitant use of PHT (OR: 11.0; 95% CI: 3.1-38.7), concomitant PB (OR: 4.3; 95% CI: 1.0-17.9), concomitant CBZ (OR: 2.8; 95% CI: 0.6-11.9), and concomitant topiramate (OR: 2.8; 95% CI: 1.2-6.5). Regimens containing multiple inducers were associated with an increased risk of hyperammonemia. Identification of risk factors for hyperammonemia associated with VPA therapy can help to minimize side effects during its clinical use.

Valproate-induced hyperammonemic encephalopathy

Valproic acid (VPA) is an effective anticonvulsant useful in many types of epilepsy and, although it is usually well tolerated, it has been associated with many neurological and systemic side effects. Among these, one of the most important is VPA-induced hyperammonemic encephalopathy (VHE): its typical signs are acute onset of impaired consciousness, focal neurologic symptoms, and increased seizure frequency. The pathogenesis of VHE is still unclear, but it has been suggested that hyperammonemia can produce encephalopathy via inhibition of glutamate uptake by astrocytes which may lead to potential neuronal injury and perhaps cerebral edema. Glutamine production is increased, whereas its release is inhibited in astrocytes exposed to ammonia. The elevated glutamine increases intracellular osmolarity, promoting an influx of water with resultant astrocytic swelling. This swelling could compromise astrocyte energy metabolism and result in cerebral edema with increased intracranial pressure. Moreover, VHE seems to be more frequently in patients with carnitine deficiency or with congenital urea cycle enzymatic defects.

Valproic Acid-Induced Hyperammonemic Encephalopathy

Objective

To review the relevant literature concerning the biochemical mechanism(s) of valproic acid (VPA)-induced hyperammonemia in an attempt to present a unifying pathogenetic hypothesis.

Data Sources

The MEDLINE database (1966–July 2001) was searched for English-language articles and abstracts on VPA-induced hyperammonemia. References cited in relevant primary articles were also reviewed.

Study Selection

More than 150 original and review articles were evaluated, and the most relevant were selected.

Data Extraction

Clinically significant hyperammonemia is a rare adverse effect of VPA therapy. The exact pathogenesis of VPA-induced hyperammonemia remains unclear, but is likely to involve a variety of contributing and possibly overlapping biochemical steps. These include VPA drug concentration, indirect inhibition of ureagenesis by valproyl coenzyme A (CoA), direct suppression of the urea cycle enzymes, depletion of mitochondrial acetyl CoA and decreased production of N-acetylglutamate, depletion of carnitine stores, and increased glutamate dehydrogenase activity.

Conclusions

Hyperammonemic encephalopathy is a rare, but clinically important, adverse effect of VPA therapy. The biochemical basis for this association remains unclear. Awareness of this adverse reaction by healthcare personnel is important in early recognition, treatment, and prevention.

Carnitine deficiency and hyperammonemia in children receiving valproic acid with and without other anticonvulsant drugs

Plasma ammonia and total and free carnitine were measured in 84 children requiring anticonvulsant drugs: 32 patients (group A) on valproic acid alone, 28 children (group B) on polytherapy including valproic acid, and 24 patients (group C) on polytherapy without valproic acid. The other anticonvulsant drugs used in groups B and C were carbamazepine and phenobarbital. Plasma ammonia concentrations were elevated in both group A and B compared with controls. Group B patients showed significantly higher hyperammonemia than group A (59.9 +/- 16.3 micrograms/dl vs. 36.7 +/- 12.4 micrograms/dl; P < 0.05). Group C patients had plasma ammonia levels similar to those of controls (31.1 +/- 14.7 micrograms/dl vs. 29.7 +/- 12.1 micrograms/dl; NS). In both group A and group B patients, plasma ammonia levels were correlated with the valproic acid dosage (r = 0.32, P < 0.01) and with serum concentrations of valproic acid (r = 0.41, P < 0.001). Moreover, a significant correlation between plasma ammonia and duration of valproic acid therapy was found in the patients as a whole (r = 0.31, P < 0.01). Plasma total and free carnitine concentrations were significantly reduced in groups A and B (total carnitine 36.9 +/- 6.9 mumol/l vs. 32.9 +/- 9.7 mumol/l; free carnitine 28.9 +/- 5.1 mumol/l vs. 25.7 +/- 4.3 mumol/l, respectively) compared with group C patients who did not receive valproic acid and in whom values were similar to controls (total carnitine 46.1 +/- 9.0 mumol/l vs. 47.7 +/- 10.1 mumol/l; free carnitine 40.1 +/- 7.1 mumol/l vs. 42.9 +/- 8.0 mumol/l, respectively). Twenty-eight patients (18 of group A and 10 of group B) were re-evaluated and showed a complete normalization of plasma ammonia, and total and free carnitine levels which were similar to controls. Our data suggest that hyperammonemia is an important problem in patients receiving valproic acid, particularly in association with other anticonvulsant drugs. This increase of plasma ammonia and the concomitant reduction of carnitine seem to be transient and completely reversible.

Valproate-induced hyperammonemia of renal origin. Effects of valproate on glutamine transport in rat kidney mitochondria

The antiepileptic sodium valproate (VPA) systematically induces an asymptomatic hyperammonemia of renal origin in fasting normal human volunteers and in fasting rats, accompanied by an increased renal glutamine uptake. Fasting rats were injected with VPA and their mitochondria isolated, or isolated mitochondria of fasting rats were incubated with VPA. Transmembranal mitochondrial glutamine uptake and activities for five mitochondrial and three cytosolic enzymes involved in ammoniagenesis were measured. In VPA-incubated mitochondria, glutamine transport increased for VPA concentrations between 10(-3) and 10(-5) M; enzyme activities did not change. In mitochondria of VPA-treated rats, Km and Vmax were unaffected. These findings reflect membrane effects of VPA observed in other experimental settings.

Valproic acid induction of coma in rats: synergism with NH4+ and pentobarbital

Dose-response curves for the incidence of coma after intraperitoneal injections of various doses of valproic acid (VP) and octanoic acid (OA) showed that, mole for mole, valproic acid was less toxic than octanoic acid. However, a simultaneous subcoma dose of pentobarbital (PB) enhanced the toxicity of VP more than that of OA. The dose-response curve for NH4Cl was affected by simultaneous subcoma doses of VP and OA but not by PB. VP enhanced the toxicity of the NH4+ by 52%; OA enhanced the toxicity by 12%. PB added significantly to the toxicity of VP and NH4+ when the three were given simultaneously. Doses of 0.7 mmol NH4+ and 0.5 mmol VP given separately had little or no encephalopathic effect, with blood ammonias of 250-1250 micrograms/dl. When given simultaneously they induced a deep coma and raised the blood ammonia threefold, to about 3600 micrograms/dl. Similar doses of OA and NH4+, induced a similar deep coma, but blood levels of ammonia were not as high. Simultaneous injections of 250 mg glucose did not alter the results. Thus VP toxicity is enhanced substantially by its synergistic interactions with PB and the NH4+.

Serum carnitine during valproic acid therapy

This study was initiated to examine the influence of valproic acid (VPA) on serum carnitine, as well as the possible etiological role of carnitine in VPA-induced fatal hepatotoxicity. Free, total, and short-chain acylcarnitine were measured in the serum of 21 pediatric patients receiving VPA therapy, 21 healthy matched controls, and 21 patients receiving various antiepileptic drugs other than VPA. The free carnitine level was lowest in the VPA group (p less than 0.05), and the short-chain acylcarnitine/free carnitine ratio was highest in the VPA group (p less than 0.01). Patients receiving VPA polytherapy had lower total carnitine values than patients receiving VPA monotherapy (p less than 0.05). No correlation was found between serum ammonia and VPA drug levels. A 3 1/2-year-old girl developed hepatic failure under VPA therapy. Her serum carnitine values were normal. Despite the oral intake of L-carnitine this patient died. In this case, apparently VPA-induced hepatotoxicity was not associated with carnitine deficiency. The reduction of carnitine in the serum of VPA-treated patients is most probably due to alterations of fatty acid metabolism. However, neither primary carnitine deficiency nor VPA-induced secondary carnitine deficiency can be the only reason for the VPA-induced fatal hepatotoxicity.

Nutritional influence on serum ammonia in young patients receiving sodium valproate

Hyperammonemia is a common side effect of valproic acid (VPA) therapy. This study was designed to investigate a potential nutritional influence on serum ammonia levels during VPA therapy. In 10 VPA-treated young patients (5 receiving monotherapy, 5 receiving VPA-primidone polytherapy), venous serum ammonia, triglycerides, and cholesterol were measured on 3 consecutive days as follows: (a) after a 13-h overnight fast; (b) 2 h after an oral fat load with butter (1.2 g fat/kg body weight); and (c) 2 h after an oral protein load with fresh cheese (1 g protein/kg body weight). Ten young adults served as controls. After protein load VPA patients had significantly higher serum ammonia levels than controls (mean: 194 vs. 75 micrograms/dl in controls; p less than 0.006). Ammonia values were higher after protein load than after fat load or after fasting (p less than 0.0001). Patients receiving polytherapy had higher ammonia levels than patients receiving monotherapy (not significant). There was no correlation to the height of serum VPA levels. Clinical symptoms attributable to hyperammonemia (vomiting, apathy) were found in only one patient, and her serum ammonia was as high as 426 micrograms/dl. Triglycerides and cholesterol did not show any VPA-induced differences. We assume that VPA alters the short-term regulation of ureasynthesis. We recommend the avoidance of high protein intake in patients receiving VPA therapy, especially in young patients receiving polytherapy or comedication, or in risk situations like serious infections.

Decrease of valproate-induced hyperammonemia in normal subjects by lipid ingestion

Sodium valproate (VPA), a branched short-chain fatty acid, always causes a hyperammonemia of renal origin in fasting man. The intake of medium-length, straight-chain fatty acids abolishes the VPA-induced hyperammonemia, and VPA free fraction increases concomitantly. Accordingly, fatty acids could be useful in preventing and treating hyperammonemia-accompanied stuporous states which are complications of VPA medication.