Topiramate-induced metabolic acidosis: report of two cases

Topiramate for Seizures in Preterm Infants and the Development of Necrotizing Enterocolitis

Neonatal seizures represent a significant health burden on the term and preterm neonatal population and are linked to poor long-term neurodevelopmental outcomes. Currently, there are no US Food and Drug Administration-approved antiepileptic drugs for neonates, and authors of the medical literature have yet to reach a consensus on the most adequate approach to neonatal seizures. Topiramate is readily used in the adult and older pediatric population for the management of migraines and partial-onset seizures. Topiramate continues to gain favor among pediatric neurologists who often recommend this medication as a third-line treatment of neonatal seizures. We report our recent experience with 4 preterm neonates, born between 2015 and 2017, who developed radiographic signs of necrotizing enterocolitis after receiving topiramate for seizures. Each was given oral topiramate for the treatment of electrographic and clinical seizures and developed the subsequent diagnosis of necrotizing enterocolitis, with abdominal distention, hemoccult-positive stools, and radiographic signs of intestinal distention and pneumatosis. More research regarding the risk factors of topiramate use in premature infants is needed.

The effect of antiepileptic drugs on the kidney function and structure

INTRODUCTION

Long-term use of antiepileptic drugs (AEDs) is associated with number of somatic conditions. Data from experimental, cross-sectional and prospective studies have evidence for the deleterious effect of some AEDs on the kidney. Areas covered: This review summarized the current knowledge of the effect of AEDs on the kidney including evidence and mechanisms. Fanconi syndrome was reported with valproate (VPA) therapy in severely disabled children with epilepsy. Renal tubular acidosis and urolithiasis were reported with acetazolamide, topirmate and zonisamide, drugs with carbonic anhydrase inhibition properties. Increased levels of urinary N-acetyl-beta-D-glucosaminidase (NAG) to urinary creatinine (U-NAG/UCr), urinary excretion of α1-micrglobulin, β-galactosidase activity; and urinary malondialdehyde to creatinine (MDA/Cr), markers of renal glomerular and tubular injury, were reported with chronic use of some AEDs (VPA, carbamazepine and phenytoin). The mechanism(s) of kidney dysfunction/injury induced by AEDs is unknown. Experimental and clinical studies have shown that VPA induces oxidative stress, mitochondrial deficits, carnitine deficiency and inflammation and fibrosis in renal tissue in mice and in vitro studies. Expert commentary: It seems reasonable to monitor kidney function during treating patients with epilepsy at high risk of kidney injury (e.g. on combined therapy with more than one AED, severely disabled children, etc).

Epilepsy, Antiepileptic Drugs, and Aggression: An Evidence-Based Review

Antiepileptic drugs (AEDs) have many benefits but also many side effects, including aggression, agitation, and irritability, in some patients with epilepsy. This article offers a comprehensive summary of current understanding of aggressive behaviors in patients with epilepsy, including an evidence-based review of aggression during AED treatment. Aggression is seen in a minority of people with epilepsy. It is rarely seizure related but is interictal, sometimes occurring as part of complex psychiatric and behavioral comorbidities, and it is sometimes associated with AED treatment. We review the common neurotransmitter systems and brain regions implicated in both epilepsy and aggression, including the GABA, glutamate, serotonin, dopamine, and noradrenaline systems and the hippocampus, amygdala, prefrontal cortex, anterior cingulate cortex, and temporal lobes. Few controlled clinical studies have used behavioral measures to specifically examine aggression with AEDs, and most evidence comes from adverse event reporting from clinical and observational studies. A systematic approach was used to identify relevant publications, and we present a comprehensive, evidence-based summary of available data surrounding aggression-related behaviors with each of the currently available AEDs in both adults and in children/adolescents with epilepsy. A psychiatric history and history of a propensity toward aggression/anger should routinely be sought from patients, family members, and carers; its presence does not preclude the use of any specific AEDs, but those most likely to be implicated in these behaviors should be used with caution in such cases.

The frequency and severity of metabolic acidosis related to topiramate

Objective

We planned a cross-sectional analysis to determine the frequency and severity of metabolic acidosis in patients taking topiramate while awaiting craniotomy.

Methods

Eighty patients (18 – 65 years) taking topiramate to control seizures while awaiting elective craniotomy were enrolled. Any signs of metabolic acidosis or topiramate-related side effects were investigated. Blood chemistry levels and arterial blood gases, including lactate, were obtained. The severity of metabolic acidosis was defined according to base excess levels as mild or moderate.

Results

Blood gas analysis showed that 71% (n = 57) of patients had metabolic acidosis. The frequency of moderate metabolic acidosis was 56% (n = 45), while that of mild metabolic acidosis was 15% (n = 12). A high respiratory rate was reported in only 10% of moderately acidotic patients.

Conclusions

In patients receiving topiramate, baseline blood gas analysis should be performed preoperatively to determine the presence and severity of metabolic acidosis.

Diabetes and epilepsy in children and adolescents

Over the last years, there has been an increasing interest in the potential association between type 1 diabetes (T1D) and epilepsy. Both T1D and epilepsy are common conditions in children and adolescents, and therefore, their association might represent simply a coincidence or be related to common underlying mechanisms with a potential causal relationship. Few epidemiological studies have been performed in the pediatric population, and they have reached discordant conclusions, with some studies reporting an increased prevalence of epilepsy in children and adolescents with T1D, whereas others have not confirmed this finding. Several mechanisms could explain the occurrence of epilepsy in young people with T1D, such as metabolic abnormalities (hypo/hyperglycemia) and autoantibodies, along with a genetic predisposition and the presence of brain lesions/damage. Further studies are required to better define whether there is a causal relationship between the two conditions and to understand the underlying mechanisms.

Metabolic disturbances and renal stone promotion on treatment with topiramate: a systematic review

AIMS

The use of topiramate, which is prescribed for the management of epilepsy, for migraine headache prophylaxis and as a weight-loss agent, has been associated with the development of metabolic acidosis, hypokalaemia and renal stone disease. We systematically reviewed all the literature.

METHODS

The systematic review of the literature was realized using the principles underlying the UK Economic and Social Research Council guidance on the conduct of narrative synthesis and the Preferred Reporting Items for Systematic Reviews and Meta-Analyses statement.

RESULTS

Fourty-seven reports published between 1996 and 2013 were retained for the final analysis. Five case-control studies and six longitudinal studies addressed the effect of topiramate on acid-base and potassium balance. A significant tendency towards mild-to-moderate hyperchloraemic metabolic acidosis (with bicarbonate ≤21.0 mmol l(-1) in approximately every third case) and mild hypokalaemia (with potassium ≤3.5 mmol l(-1) in 10% of the cases) was noted on treatment with topiramate, which was similar in children and adults. A single study observed that topiramate causes mild hyperuricaemia in male adults. A tendency towards hypocitraturia, a recognized promoter of renal stone formation, was noted in all patients on topiramate.

CONCLUSIONS

Increasing evidence supports the use of topiramate. Topiramate is generally well tolerated, and serious adverse events are rare. Nonetheless, the present systematic review of the literature indicates that its use is linked with the development of acidosis, hypokalaemia, hyperuricaemia and hypocitraturia.

Topiramate for the treatment of epilepsy and other nervous system disorders

Initially synthesized as an oral hypoglycemic agent, topiramate was approved for use as an anticonvulsant in 1996. Its broad spectrum efficacy in epilepsy, including as monotherapy and in children, is well established. Topiramate has also been used in the management of nonepileptic neurologic and psychiatric conditions, including migraine prophylaxis (with firmly established efficacy), obesity (with some evidence of long-term maintenance of weight loss), substance dependence, bipolar disorder and neuropathic pain, and it has been investigated as a possible neuroprotective agent. Paresthesias and cognitive side effects are the most common troublesome adverse effects. Recent trends towards lower doses may help achieve the best combination of efficacy and tolerability.

Prevalence and spot urine risk factors for renal stones in children taking topiramate

INTRODUCTION

Topiramate (TPM), an anti-epileptic drug with >4 million users, increases renal stones in adults. We screened outpatient TPM-treated children without history of stones to estimate the prevalence of renal stones and to characterize urine stone-risk profiles.

METHODS

Children taking TPM ≥1 month underwent an interview, renal ultrasound, and spot urine testing in this prospective study. Normal spot urine values were defined as: calcium/creatinine ratio ≤0.20 mg/mg (>12 months) or ≤0.60 mg/mg (≤12 months), citrate/creatinine ratio >0.50 mg/mg, and pH ≤ 6.7.

RESULTS

Of 41 patients with average age of 9.2 years (range 0.5-18.7), mean TPM dose of 8.0 mg/kg/day (range 1.4-23.6), and mean treatment duration of 27 months (range 1-112), two (4.9%) had renal stones. The majority of children taking TPM had lithogenic abnormalities on spot urine testing, including 21 (51%) with hypercalciuria, 38 (93%) with hypocitraturia, and 28 (68%) with pH ≥ 6.7. Hypercalciuria and hypocitraturia were independent of TPM dose and duration; urine pH increased with dose. 24-h urine parameters improved in 1 stone-former once TPM was weaned.

CONCLUSIONS

Asymptomatic stones were found in 2/41 (4.8%) children taking TPM. Risk factors for stones were present in the spot urine of most children, including hypocitraturia (93%) and hypercalciuria (51%), independent of TPM dose and duration. High urine pH, found in 68%, correlated with TPM dose. Pediatric specialists should be aware of increased risks for stones, hypercalciuria, hypocitraturia, and alkaline urine in children taking TPM.

Association of epilepsy and type 1 diabetes mellitus in children and adolescents: is there an increased risk for diabetic ketoacidosis?

OBJECTIVE

To estimate the prevalence of epilepsy and possible risk factors in children and adolescents with diabetes mellitus.

STUDY DESIGN

We conducted an observational cohort study based on the Diabetes Patienten Verlaufsdokumentation database including data from 45 851 patients (52% male) with type 1 diabetes mellitus, age 13.9 ± 4.3 years (mean ± SD) and duration of diabetes mellitus 5.4 ± 4.2 years. The database was searched for the concomitant diagnosis of epilepsy or epileptic convulsions and for antiepileptic medication.

RESULTS

A total of 705 patients with epilepsy were identified, giving a prevalence of 15.5 of 1000. A total of 375 patients were treated with antiepileptic medication, and 330 patients were without anticonvulsive therapy. Patients with epilepsy were younger at onset of diabetes mellitus and shorter than patients without epilepsy, and their weight and body mass index were comparable. No difference could be demonstrated for metabolic control, type of insulin treatment, insulin dose, and prevalence of B-cell specific autoantibodies. The frequency of severe hypoglycemia was lower in patients treated with antiepileptic medication. The risk for diabetic ketoacidosis was almost double in patients with epilepsy compared with patients with type 1 diabetes mellitus alone (P < .01).

CONCLUSION

Children and adolescents with diabetes mellitus show an increased prevalence of epileptic seizures. For unknown reasons, there is an association between epilepsy and diabetic ketoacidosis in children with type 1 diabetes mellitus.

Long-term open-label study of adjunctive topiramate in infants with refractory partial-onset seizures

Data from 2 studies (phase 1 and phase 3) in infants <2 years old (N = 284; mean [SD] age, 12[6.3] months) with refractory partial-onset seizures were pooled to assess the long-term safety up to 1 year (primary objective) and tolerability of adjunctive topiramate treatment (mean treatment duration = 282 days). Monthly seizure rate summaries were also assessed. During the open-label extensions of these studies, study medication was first titrated to a dose of 25 mg/kg/d with subsequent uptitration to the maximum dosage tolerated, or seizure freedom, or a maximum of 60 mg/kg/d, whichever occurred first. The most common treatment-emergent adverse events (≥30%) were fever (52%), respiratory tract infections (51%), anorexia (35%), and acidosis (31%). Mean (SD) changes from pretreatment baseline to endpoint in Z scores for growth parameters were as follows: -0.82 (1.19) (body weight), -0.45 (1.60) (body length), and -0.36 (1.02) (head circumference).Tolerability in infants was consistent with previous studies.

Chronic impact of topiramate on acid-base balance and potassium in childhood

Topiramate, which is commonly prescribed for seizure disorders and migraine prophylaxis, sometimes causes metabolic acidosis and hypokalemia. Since the effects of topiramate on acid-base balance and potassium levels have not been well explored in children, acid-base balance, anion gap and potassium were assessed in 24 patients (8 females and 16 males) aged between 4.6 and 19 years on topiramate for more than 12 months and in an age-matched control group. Plasma bicarbonate (21.7 versus 23.4 mmol/L; P<0.03), carbon dioxide pressure (39.7 versus 43.2mm Hg; P<0.05), and potassium (3.7 versus 4.0 mmol/L; P<0.03) were on the average lower and chloride (109 versus 107 mmol/L; P<0.03) higher in patients treated with topiramate than in controls. Blood pH, plasma sodium and the anion gap were similar in patients on topiramate and in controls. In patients on topiramate no significant correlation was observed between the dosage of this agent and plasma bicarbonate or potassium as well as between topiramate blood level and the mentioned electrolytes. In conclusion long-term topiramate treatment is associated with a mild, statistically significant tendency towards compensated normal anion gap metabolic acidosis and hypokalemia.

Use of second-generation antiepileptic drugs in the pediatric population

Epilepsy is common in the pediatric population. Nine second-generation antiepileptic drugs have been approved in the US for use in epilepsy over the past 15 years: felbamate, gabapentin, lamotrigine, topiramate, tiagabine, levetiracetam, oxcarbazepine, zonisamide, and pregabalin. Their use in pediatric patients is fairly widespread, despite most of these agents not having US FDA indications for use. Felbamate and gabapentin were the first two second-generation antiepileptic drugs to be approved in the US. Felbamate use has been limited because of the occurrence of hepatotoxicity and aplastic anemia. Although gabapentin is a fairly well tolerated antiepileptic drug, its use has also been limited as a result of inconsistent efficacy and concern about seizure exacerbation. Lamotrigine and topiramate are broad-spectrum antiepileptic drugs with efficacy in a wide variety of seizure types. Both agents have some tolerability concerns: rash with lamotrigine and neuropsychiatric events with topiramate. There are very little data on tiagabine use in children, but this agent appears to be effective and to have a good tolerability profile. Levetiracetam is a second-generation antiepileptic agent that is available intravenously. Considering its good efficacy, fast onset of action, and low incidence of serious adverse effects, its use in the acute setting could potentially increase. Oxcarbazepine and zonisamide have been relatively well studied in pediatric seizure patients, including use as monotherapy. Both agents have demonstrated good efficacy and tolerability for patients as young as 1 month old. Vigabatrin and rufinamide are currently not available in the US, but have been shown to have some success in other countries. Pregabalin is the newest antiepileptic agent, but lacks pediatric data currently.

Hyperventilation and cerebrospinal fluid acidosis caused by topiramate

OBJECTIVE

To report a case of hyperventilation caused by topiramate therapy and propose a pathophysiologic mechanism for this disorder.

CASE SUMMARY

A 52-year-old woman with refractory seizure disorder was admitted to the burn care unit with burns over 10% of her body. Her seizure medications, unchanged and well tolerated for several months, included carbamazepine 1200 mg, lamotrigine 500 mg, phenobarbital 80 mg, and topiramate 150 mg per day. During hospitalization, despite a relatively normal arterial pH, the woman developed persistent hyperventilation, with respiratory rates up to 50 breaths/min. Alkalinization did not reduce the hyperventilation. Thoracic contrast-enhanced computed tomographic scan ruled out pulmonary embolism and persistent pneumonia. Salicylate and biguanide screening were negative; results of repeated thyroid and liver function tests were normal. Cerebral magnetic resonance imaging excluded a cerebral pathology. After cerebrospinal fluid (CSF) analysis showed acidosis (pH 7.14), topiramate was withdrawn and the patient's general condition rapidly improved. Forty-eight hours later, the CSF pH had increased to 7.26. The woman was discharged from the burn care unit on the 42nd hospital day.

DISCUSSION

Hyperchloremic normal anion gap metabolic acidosis, which can lead to hyperventilation, has been reported as an adverse effect of topiramate treatment. However, our patient had respiratory alkalosis. Concurrent etiologies of peripheral hyperventilation were excluded, leaving central neurogenic hyperventilation as the remaining etiology. Such central neurogenic hyperventilation associated with topiramate has previously been reported in intensive care. Our case report demonstrates CSF acidosis. Withdrawing topiramate reduced both CSF acidosis and hyperventilation. The mechanism of topiramate-induced CSF acidosis remains unclear. According to the Naranjo probability scale, the relationship of hyperventilation to administration of topiramate in our patient was probable.

CONCLUSIONS

Normal doses of topiramate may provoke central neurogenic hyperventilation, as a result of CSF acidosis. The acid-base status of critically ill patients receiving topiramate should be monitored carefully.

Molecular pharmacodynamics, clinical therapeutics, and pharmacokinetics of topiramate

Topiramate (TPM; TOPAMAX) is a broad-spectrum antiepileptic drug (AED) that is approved in many world markets for preventing or reducing the frequency of epileptic seizures (as monotherapy or adjunctive therapy), and for the prophylaxis of migraine. TPM, a sulfamate derivative of the naturally occurring sugar D-fructose, possesses several pharmacodynamic properties that may contribute to its clinically useful attributes, and to its observed adverse effects. The sulfamate moiety is essential, but not sufficient, for its pharmacodynamic properties. In this review, we discuss the known pharmacodynamic and pharmacokinetic properties of TPM, as well as its various clinically beneficial and adverse effects.

Canadian Network for Mood and Anxiety Treatments (CANMAT) guidelines for the management of patients with bipolar disorder: update 2007

In 2005, the Canadian Network for Mood and Anxiety Treatments (CANMAT) published guidelines for the management of bipolar disorder. This update reviews new evidence since the previous publication and incorporates recommendations based on the most current evidence for treatment of various phases of bipolar disorder. It is designed to be used in conjunction with the 2005 CANMAT Guidelines. The recommendations for the management of acute mania remain mostly unchanged. Lithium, valproate and several atypical antipsychotics continue to be recommended as first-line treatments for acute mania. For the management of bipolar depression, new data support quetiapine monotherapy as a first-line option. Lithium and lamotrigine monotherapy, olanzapine plus selective serotonin reuptake inhibitors (SSRI), and lithium or divalproex plus SSRI/bupropion continue to remain the other first-line options. First-line options in the maintenance treatment of bipolar disorder continue to be lithium, lamotrigine, valproate and olanzapine. There is recent evidence to support the combination of olanzapine and fluoxetine as a second-line maintenance therapy for bipolar depression. New data also support quetiapine monotherapy as a second-line option for the management of acute bipolar II depression. The importance of comorbid psychiatric and medical conditions cannot be understated, and this update provides an expanded look at the prevalence, impact and management of comorbid conditions in patients with bipolar disorder.

New Anticonvulsants—New Adverse Effects

Ongoing refinements in pharmacology continue to provide new medications for the treatment of seizure disorders and other neurologic conditions. The authors present the cases of two children who developed relatively uncommon adverse effects to new anticonvulsant medications, including metabolic acidosis with topiramate and hyponatremia with oxcarbazepine. In one of our two patients, intraoperative acidosis related to topiramate was noted. Appropriate investigation with documentation of normal serum lactate resulted in the exclusion of other potentially serious causes of acidosis and in the identification of topiramate as the causative agent. In our second patient, hyponatremia and status epilepticus resulted from therapy with oxcarbazepine. Prompt recognition of hyponatremia, fluid restriction, and cessation of oxcarbazepine therapy resulted in prompt correction of the hyponatremia. We review previous reports of these adverse effects with topiramate and oxcarbazepine, describe the pathophysiology of these metabolic alterations, provide treatment strategies, and make suggestions for monitoring patients during therapy with these anticonvulsant medications.

Topiramate as an Adjuvant Treatment With Atypical Antipsychotics in Schizophrenic Patients Experiencing Weight Gain

Schizophrenic patients commonly suffer weight gain, which is often associated with widely prescribed antipsychotic medicines. It is distressing to most patients who experience it and may affect their response to treatment of schizophrenia. Weight gain is also associated with treatment noncompliance and several medical conditions. This study explored the efficacy and tolerability of topiramate as an adjuvant treatment of patients with schizophrenia who were carrying excess weight. In this 12-week, randomized, placebo-controlled prospective study, 66 hospitalized patients with schizophrenia who were carrying excess weight were given topiramate at doses of 100 mg/day or 200 mg/day, or a placebo. The primary measures made were body weight, body mass index, waist measurement, hip measurement, and waist-to-hip ratio. Safety measures included physical examinations and the monitoring of adverse effects, clinical laboratory data, and vital signs. The Clinical Global Impression-Severity of Illness scale (CGI-S) and the Brief Psychiatric Rating Scale (BPRS) were used to quantify changes in schizophrenic symptoms and signs. In the 200-mg/day topiramate group, body weight, body mass index, waist measurement, and hip measurement decreased significantly compared with the 100-mg/day topiramate and placebo groups over 12 weeks. However, the waist-to-hip ratio did not change in any group. Scores on the CGI-S and BPRS decreased significantly over the 12-week period in both topiramate groups, but the decrease was not clinically meaningful. These results suggest that a higher dose of topiramate is efficacious as an adjuvant treatment of patients with schizophrenia experiencing excess weight gain. Further clinical research is required to establish guidelines for the use of topiramate as an antiobesity agent in schizophrenic patients.

Topiramate and severe metabolic acidosis: case report

Topiramate infrequently induces anion gap metabolic acidosis through carbonic anhydrase inhibition on the distal tubule of the nephron - a type 2 renal tubular acidosis. We report on a 40 years old woman previously healthy that developed significant asymptomatic metabolic acidosis during topiramate therapy at a dosage of 100mg/day for three months. Stopping medication was followed by normalization of the acid-base status within five weeks. This infrequent side effect appears unpredictable and should be given careful attention.

Carbonic anhydrase inhibitors. Zonisamide is an effective inhibitor of the cytosolic isozyme II and mitochondrial isozyme V: solution and X-ray crystallographic studies

The antiepileptic drug zonisamide was considered to act as a weak inhibitor of the zinc enzyme carbonic anhydrase (CA, EC 4.2.1.1) (with a K(I) of 4.3 microM against the cytosolic isozyme II). Here we prove that this is not true. Indeed, testing zonisamide in the classical assay conditions of the CO2 hydrase activity of hCA II, with incubation times of enzyme and inhibitor solution of 15 min, a K(I) of 10.3 microM has been obtained. However, when the incubation between enzyme and inhibitor was prolonged to 1 h, the obtained K(I) was of 35.2 nM, of the same order of magnitude as that of the clinically used sulfonamides/sulfamates acetazolamide, methazolamide, ethoxzolamide and topiramate (K(I)s in the range of 5.4-15.4 nM). The inhibition of the human mitochondrial isozyme hCA V with these compounds has been also tested by means of a dansylamide competition binding assay, which showed zonisamide and topiramate to be effective inhibitors, with K(I)s in the range of 20.6-25.4 nM. The X-ray crystal structure of the adduct of hCA II with zonisamide has also been solved at a resolution of 1.70 A, showing that the sulfonamide moiety participates in the classical interactions with the Zn(II) ion and the residues Thr199 and Glu106, whereas the benzisoxazole ring is oriented toward the hydrophobic half of the active site, establishing a large number of strong van der Waals interactions (<4.5 A) with residues Gln92, Val121, Phe131, Leu198, Thr200, Pro202.

Topiramate and metabolic acidosis: a case series and review of the literature

Topiramate is a new anticonvulsant drug recommended for treatment of partial and generalized seizures in children and adults. It has been found to cause a nonanion gap metabolic acidosis in some patients, which is related to carbonic anhydrase inhibition. This adverse reaction is more common in children than adults and is rarely symptomatic. Clinicians need to be aware of this potential side effect especially in children undergoing major surgery. Children who are treated with topiramate should have a careful history taken preoperatively looking for signs of a metabolic acidosis and baseline blood chemistries should be measured prior to surgery to detect an asymptomatic metabolic acidosis.

Intentional Topiramate Ingestion in an Adolescent Female

OBJECTIVE:

To describe an intentional topiramate ingestion by an adolescent and warn of the potential for topiramate abuse.

CASE SUMMARY:

A 17-year-old female intentionally ingested approximately eight 100-mg topiramate tablets for the purpose of “getting high.” Soon after ingestion, she was found at school obtunded and nonresponsive. Upon transfer to the emergency department, she became combative and aggressive with evolving neurologic abnormalities including incoherence, confusion, disorientation, and significant speech impairments including echolalia. Approximately 24 hours after ingestion, the patient had completely recovered without requiring specific treatment or experiencing sequelae.

DISCUSSION:

The clinical effects following acute topiramate intoxication appear consistent with the drug's known pharmacologic properties. There are few other reports of topiramate ingestions and most cases have had mild outcomes.

CONCLUSIONS:

Due to the multifactorial effects topiramate may have upon the central nervous system and its anorectic effect, abuse of this drug by adolescents should be considered upon presentation of an adolescent with mental status changes.

Side Effects of Antiepileptics- A Review

Older generation antiepileptic drugs like Phenobarbital (Luminal), carbamazepine (Tegretol), phenytoin (Dilantin), and valproic acid (Depakote) have several shortcomings such as suboptimal response rates, significant adverse effects, several drug interactions, and a narrow therapeutic index. New antiepileptic drugs have been developed in the last decade to overcome some of these problems. These newer generation antiepileptics like felbamate (Felbatol), gabapentin (Neurontin), lamotrigine (Lamictal), levetiracetam (Keppra), oxcarbazepine (Trileptal), tiagabine (Gabitril), topiramate (Topamax), and zonisamide (Zonegran) have better tolerability profiles, low interaction potential, and significantly less enzyme inducing or inhibiting properties. As the use of antiepileptic drugs has expanded to include treatment of neuropathic pain, newer side effects have been reported. In addition to the common side effects of antiepileptic drugs, like dizziness, drowsiness, and mental slowing; other side effects like weight gain, metabolic acidosis, nephrolithiasis, angle closure glaucoma, skin rash, hepatotoxicity, colitis, and movement and behavioral disorders, to name a few, have been brought to our attention. This review is an attempt to highlight the features and incidences of some of these side effects.

Acute topiramate toxicity

Topiramate (Topamax) is an anti-epileptic medication for which acute toxicity is infrequently reported. A 5-yr-old girl, not previously taking topiramate, developed neurological symptoms after acute ingestion of this medication. She was intermittently agitated, complained of "not being able to feel anything," demonstrated arching movements of the back, and perseverated upon questioning. Computerized tomography of the head and electroencephalography were both normal, and urine toxicology testing for drugs of abuse was negative. A serum topiramate level was 10.5 mcg/mL, confirming the ingestion. The patient was observed for 24 h, over which time her symptoms completely resolved.

Concomitant treatment with topiramate and ketogenic diet in pediatric epilepsy

PURPOSE

Topiramate (TPM) is widely used as add-on therapy for epilepsy. TPM inhibits carbonic anhydrase, which may result in metabolic acidosis from decreased serum bicarbonate. The ketogenic diet (KGD) predisposes patients to metabolic acidosis, especially during induction. In children with refractory epilepsy, cotreatment with TPM and KGD may be considered, but special attention should be paid to the combined risks for metabolic acidosis and nephrolithiasis. We report our experience in 14 children cotreated with TPM and the KGD.

METHODS

Medical records of 14 children cotreated with the KGD and TPM for medically refractory epilepsy were reviewed retrospectively. Bicarbonate levels were analyzed and correlated with clinical profiles, including duration of cotreatment, TPM dose, KGD ratio, and seizure control.

RESULTS

Nine children had a <20% decrease in bicarbonate levels, from 5.3 to 12.3 mEq/L (mean, 7.6 mEq/L). Cotreatment was continued in all patients for duration of 33 to 544 days (seven had remained on cotreatment at the end of the study period), although two children required bicarbonate supplements to continue the KGD. No patient had nephrolithiasis.

CONCLUSIONS

Although a large decrease in bicarbonate level occurred in the majority of children, the decrease appeared mostly at the time of KGD induction when added to prior TPM therapy. Bicarbonate levels should be monitored carefully with TPM and KGD cotreatment, and bicarbonate supplements given when symptomatic.