Topiramate and its clinical applications in epilepsy

Effect of topiramate on acid-base balance: extent, mechanism and effects

Topiramate is licensed for the treatment of epilepsy and for migraine prophylaxis, but is also used off-licence for a wide range of indications. With the increasing use of topiramate, reports have emerged that topiramate can cause metabolic acidosis in some patients. It does this by impairing both the normal reabsorption of filtered HCO(3)(-) by the proximal renal tubule and the excretion of H(+) by the distal renal tubule. This combination of defects is termed mixed renal tubular acidosis (RTA). The mechanism involves the inhibition of the enzyme carbonic anhydrase, which is consistent with the fact that genetic deficiency of carbonic anhydrase is associated with mixed RTA. Topiramate-induced RTA can make patients acutely ill, and chronically, can lead to nephrolithiasis, osteoporosis and, in children, growth retardation. There is no proven method for predicting or preventing the effect of topiramate on acid-base balance, but patients with a history of renal calculi or known RTA should not receive topiramate. The utility of regular monitoring of HCO(3)(-) levels has not been proven and is not routine practice currently. For patients with persistent RTA, topiramate should usually be discontinued as alternative agents are available.

Topiramate concentrations in neonates treated with prolonged whole body hypothermia for hypoxic ischemic encephalopathy

PURPOSE

Therapeutic hypothermia reduces mortality and neurologic impairment in neonates with hypoxic-ischemic encephalopathy. Topiramate exerts a neuroprotective effect in asphyxiated neonatal animal models. However, no studies have investigated the association of hypothermia and topiramate, because topiramate pharmacokinetics during hypothermia and the optimal administration schedule are unknown. The influence of hypothermia on topiramate pharmacokinetics was evaluated in asphyxiated neonates treated with prolonged whole-body hypothermia and topiramate.

METHODS

Thirteen term newborns were treated with mild or deep whole body hypothermia for 72 h; all received oral topiramate, 5 mg/kg once a day for the first 3 days of life, and seven had concomitant phenobarbital treatment. Topiramate concentrations were measured on serial dried blood spots.

RESULTS

Topiramate concentrations were within the reference range in 11 of 13 newborns, whereas concentrations exceeded the upper limit in 2 of 13, both newborns on deep hypothermia. Topiramate concentrations reached a virtual steady state in nine newborns, for whom pharmacokinetic parameters were calculated. Values of topiramate maximal and minimal concentration, half-life, average concentration, and area under the time-concentration curve resulted in considerably higher values than those reported in normothermic infants. With respect to normothermic infants, time of maximal concentration was mildly delayed and apparent total body clearance was lower, suggesting slower absorption and elimination. Pharmacokinetic parameters did not differ significantly between infants on deep versus mild hypothermia and in those on topiramate monotherapy versus add-on phenobarbital.

CONCLUSION

Most neonates on prolonged hypothermia treated with topiramate 5 mg/kg once a day exhibited drug concentrations within the reference range for the entire treatment duration.

Rapid assay of topiramate in dried blood spots by a new liquid chromatography-tandem mass spectrometric method

Topiramate (TPM) is a new antiepiletic drug with efficacy in several types of seizures. Therapeutic drug monitoring of TPM is essential for effective patient management. The aim of this study was to evaluate the use of dried blood spot (DBS) specimens to determinate the TPM levels during the treatment. Advantages of DBS include short collection time, low invasiveness, ease and low cost of sample collection, transport and storage. Performance comparison between this method and the commercially available fluorescence-polarization immunoassay (FPIA) was made. The analysis was performed in selected reaction monitoring (SRM) mode. The calibration curve in matrix using D(12)-topiramate was linear in the concentration range of 0.0166-1.66mg/L (0.5-50mg/L in DBS) of topiramate with correlation coefficient value of 0.9985. In the concentration range of 0.5-50mg/L, the coefficients of variation in DBS were in the range 2.13-11.85% and the accuracy ranged from 93.93% to 110.67%. There was no significant differences between the concentrations (ranging 0.5-50mg/L) measured both FPIA on venous samples and LC-MS/MS assay on simultaneous DBS samples. The sensitivity and specificity of tandem mass spectrometry allow now high throughput topiramate analysis (the improvement was three times in comparison with FPIA). This new assay has favourable characteristics being highly precise and accurate. FPIA also proved to be precise and accurate, but is not always suitable for the sample collection in neonates in whom obtaining larger blood samples is not convenient or possible.

An update on the pharmacological management of post-herpetic neuralgia and painful diabetic neuropathy

Neuropathic pain is a persistent pain condition that develops secondary to nerve injury. The two most common types of peripheral neuropathic pain are post-herpetic neuralgia (PHN) and painful diabetic neuropathy (PDN). Amitriptyline, nortriptyline, desipramine and imipramine are TCAs that have been shown to be effective for the symptomatic relief of PHN and PDN. Serotonin noradrenaline reuptake inhibitors (SNRIs) such as venlafaxine and duloxetine have been shown to be very promising for the treatment of PDN with fewer adverse effects than TCAs. Selective serotonin reuptake inhibitors (SSRIs) were shown in a number of studies to have some efficacy in relieving PDN-related pain, yet other studies of the SSRIs have demonstrated conflicting outcomes. Most of the older antiepileptic studies were performed in patients with PDN; consequently, little is known about the efficacy of these drugs in patients with PHN. Carbamazepine, phenytoin and valproic acid were shown to be effective in ameliorating PDN-related pain. Other antiepileptic agents, including lamotrigine, oxcarbazepine and topiramate, have demonstrated some beneficial effects for the treatment of PDN, although they were also found to be ineffective in some PDN studies. alpha2delta Ligands such as gabapentin and pregabalin have been proven to be effective for the treatment of PHN and PDN in a number of large placebo-controlled trials. These drugs are useful not only in relieving pain but also in improving quality of life. Although the use of opioids for the treatment of neuropathic pain is controversial, a number of studies support the efficacy and safety of opioids in the treatment of neuropathic pain. Of these, oxycodone and tramadol have been shown to be superior to placebo for the treatment of PHN and PDN. A number of small studies have shown that dextromethorphan was effective in patients with PDN but not in patients with PHN. Topical agents such as lidocaine 5% patches and topical capsaicin are useful in ameliorating pain in patients with PHN but these agents are unsatisfactory for use as a sole agent. Although a number of drug treatments are available for the symptomatic relief of neuropathic pain symptoms, these agents do not provide satisfactory relief in all patients. For these patients, other treatment alternatives such as combination drug therapy that produces pain relief via distinctly different mechanisms may be successful. The purpose of this review is to compare the efficacy and limitations of currently available pharmacological treatments for the symptomatic relief of PHN and PDN, and to discuss the potential of combination therapy in PHN and PDN.

Spotlight on topiramate in epilepsy

Topiramate (Topamax) is a structurally novel broad-spectrum antiepileptic drug (AED) with established efficacy as monotherapy or adjunctive therapy in the treatment of adult and paediatric patients with generalized tonic-clonic seizures, partial seizures with or without generalized seizures, and seizures associated with Lennox-Gastaut syndrome. The incidence and severity of many adverse events, including CNS-related events, may be reduced through the use of slow titration to effective and well tolerated dosages. It is associated with few clinically significant interactions with other drugs, is effective when used with other AEDs, is not associated with drug-induced weight gain and, at lower dosages, does not interfere with the effectiveness of oral contraceptives. Therefore, topiramate is a valuable option as monotherapy or adjunctive therapy in the treatment of epilepsy in adult and paediatric patients.

Adiponectin receptor R1 is upregulated by valproic acid but not by topiramate in human hepatoma cell line, HepG2

Valproic acid (VPA) is an effective and widely used anticonvulsant, associated with metabolic adverse effects such as weight gain, hyperinsulinemia, hyperleptinemia and hypoadiponectinemia. The aim of this study was to evaluate the influence of VPA and topiramate (TPM) on adiponectin binding receptors, adipoR1 and adipoR2, in human liver cancer cells, HepG2. AdipoR1 but not adipoR2 gene expression was upregulated by VPA treatment. TPM did neither affect adipoR1 nor adipoR2 gene expression. Given the tight association between VPA treatment, metabolic side effects and the adipocytokine-axis, upregulation of adipoR1 possibly represents a favoured and insulin-sensitizing mechanism.

Topiramate and type 2 diabetes: an old wine in a new bottle

Topiramate, a marketed antiepileptic drug, has been used to treat seizures and allied neurological problems since 1999. Recently, a series of newer findings for the use of topiramate have cropped up, which include Type 2 diabetes and obesity. In a series of clinical studies, a subset of neurological patients with Type 2 diabetes mellitus (T2DM) serendipitously showed better glycaemic control when treated with topiramate. It has since been demonstrated that topiramate can act both as an insulin secretagogue and sensitiser in T2DM animal models. Pathogenesis of Type 2 diabetes involves both beta-cell dysfunction and insulin resistance. Therefore, an agent that has dual action (insulin secretagougue and sensitisation) is preferred for T2DM. Topiramate seems to act through multiple mechanisms to ameliorate diabetic symptoms, some of them unknown. Hence, it becomes imperative to discuss its probable modes of action. Topiramate raises new hope as an antidiabetic agent or a potential new chemotype with a better safety profile for the treatment of T2DM.

Topiramate in children and adolescents with epilepsy and mental retardation: a prospective study on behavior and cognitive effects

The aim of the present study was to assess the behavioral and cognitive effects following treatment with topiramate in children and adolescents with epilepsy with mild to profound mental retardation. The study group comprised 29 children, 16 males and 13 females, aged 3 to 19 years, affected by partial (4) and generalized (25) crypto/symptomatic epilepsy and mental retardation (7 mild, 5 moderate, 15 severe, 2 profound), who were administered topiramate (TPM) as add-on therapy to their baseline antiepileptic treatment. At baseline, 3 months, 6 months, and 12 months, parents or caregivers of each patient were administered a questionnaire based on the Holmfrid Quality of Life Inventory. After a 3-month follow-up, the add-on topiramate caused overall mild to moderate cognitive/behavioral worsening in about 70% of children and adolescents with mental retardation and epilepsy. After 6 and 12 months of follow-up, global worsening persisted in 31 and 20.1% of cases, respectively. In conclusion, this trial confirms that TPM can have significant adverse cognitive and behavioral side effects, even in mentally disabled children and adolescents.

Topiramate: a review of its use in the treatment of epilepsy

Topiramate (Topamax) is a structurally novel broad-spectrum antiepileptic drug (AED) with established efficacy as monotherapy or adjunctive therapy in the treatment of adult and paediatric patients with generalised tonic-clonic seizures, partial seizures with or without generalised seizures, and seizures associated with Lennox-Gastaut syndrome. The incidence and severity of many adverse events, including CNS-related events, may be reduced through the use of slow titration to effective and well tolerated dosages. It is associated with few clinically significant interactions with other drugs, is effective when used with other AEDs, is not associated with drug-induced weight gain and, at lower dosages, does not interfere with the effectiveness of oral contraceptives. Therefore, topiramate is a valuable option as monotherapy or adjunctive therapy in the treatment of epilepsy in adult and paediatric patients.

Epilepsy and kleptomania

Kleptomania, defined in the American Psychiatric Association's Diagnostic and Statistical Manua of Mental Disorders, Text Revision: DSM-IV-TR, as the inability to resist the impulse to steal objects that are not needed for personal use or for their monetary value, may reflect a form of obsessive-compulsive spectrum disorder and/or affective spectrum disorder. We report on a patient who developed kleptomania and left temporal lobe epilepsy around the same time; both disorders were completely resolved in this patient with topiramate.

Outcome and tolerability of topiramate in brain tumor associated epilepsy

Epilepsy in brain tumor patients is often refractory to pharmacological treatments and can complicate the therapeutic management of these patients. We conducted a prospective, observational study. The aim of this study was to investigate the efficacy and tolerability of topiramate (TPM) in brain tumor associated epilepsy. We studied 47 patients with brain tumors and epilepsy. The entire group was administered AEDs. TPM was the first therapeutic choice in 14 patients, while in the remaining 33 patients previous AEDs were modified and TPM was introduced due to side effects or inefficacy of the first drug. Follow-up ranged from 3 to 48 months (mean 16.5 months). Considering the final follow-up of each patient who assumed TPM for at least 3 months, we observed 45 patients: 25 were seizure free (55.6%), 9 had a reduction of seizure frequency (SF) higher than 50% (20%) and 11 were stable (24.4%). TPM responder rate was 75.6%. Three patients (6.4%) discontinued TPM for severe side effects (1 after 4 months and 2 after 1 month) and 4 (8.5%) had mild and reversible side effects. In the group of patients who had been in therapy with other AEDs prior to entering the study (n = 33), 19 patients had side effects (57.6%). During follow-up, the haematological parameters were in the normative ranges. Tumor-related seizures are difficult to control with AEDs; the precise reasons for this difficulty are not yet clear. Using TPM, we obtained good seizure control with a low incidence of side effects.

Tolerability and Safety of Topiramate in Chinese Patients with Epilepsy

OBJECTIVES

This study focused on (i) evaluating the long-term tolerability and safety of topiramate in Chinese patients with epilepsy, and (ii) comparing the tolerability and safety of topiramate monotherapy versus polytherapy in the same population.

METHODS

This was a prospective, open-label, long-term (36 months) clinical trial. 320 patients (275 adults and 45 children) with epilepsy were recruited into the study; of these, 156 patients had generalised seizures, 151 patients had partial seizures and 13 patients had unclassifiable seizures. All patients received topiramate approximately 200 mg/day either as monotherapy or as adjunctive therapy. At each visit, a physical examination and routine laboratory analysis were performed, and the adverse event (AE) profile was obtained by face-to-face interview.

RESULTS

268 patients received topiramate <or=100 mg/day and 52 patients received topiramate 100-200 mg/day. Topiramate-associated AEs occurred in 98 patients (30.6%). The most common AEs were weight loss in 18 patients (8.4%), paraesthesias in 17 (7.2%), poor memory in ten (3.8%), and dizziness in six (2.8%). Most AEs were mild to moderate and transitory; discontinuation of topiramate was observed in 13 patients (4.1%) as a result of AEs such as impaired memory (seven patients [54%]), paraesthesias (four patients [31%]), and weight loss and cutaneous reaction (each one patient [7.5% each]). The rate of AEs was significantly higher with use of topiramate as monotherapy than as adjunctive therapy (68 patients vs 30 patients [47.8% vs 16.4%], respectively).

CONCLUSION

Topiramate is well tolerated in Chinese patients with epilepsy in clinical practice. Compared with its use as adjunctive therapy, topiramate monotherapy is associated with a significantly higher frequency of adverse events.

Mechanisms of action of antiepileptic drugs

The management of seizures in the patient with epilepsy relies heavily on antiepileptic drug (AED) therapy. Fortunately, for a large percentage of patients, AEDs provide excellent seizure control at doses that do not adversely affect normal function. At the molecular level, the majority of AEDs are thought to modify excitatory and inhibitory neurotransmission through effects on voltage-gated ion channels (e.g., sodium and calcium) and gamma-aminobutyric acid (GABA)(A) receptors, respectively. In addition to these effects, two of the "second-generation" AEDs have been found to limit glutamate-mediated excitatory neurotransmission (i.e., felbamate and topiramate). Not surprisingly, those AEDs with broad spectrum clinical activity are often found to exert an action at more than one molecular target. Emerging evidence suggests that receptor and voltage-gated subunits are modified by chronic seizures. Thus, attempts to understand the relationship between target and effect continue to provide important information about the neuropathology of the epileptic network and to facilitate the development of novel therapies for the treatment of refractory epilepsy.