Review of controlled trials of gabitril (tiagabine): a clinician's viewpoint

The effects of valproate on serum leptin, insulin, and lipid levels in epileptic children

BACKGROUND

Weight gain is an important adverse effect of valproate (VPA) therapy. A number of mechanisms have been proposed for its pathophysiology. The aim of the present study is the evaluation of insulin, leptin and lipid levels in epileptic children on treatment with VPA.

METHODS

Thirty epileptic children treated with VPA, and 20 age-sex-matched healthy children, were enrolled in this study. Blood samples were taken and the body mass index was calculated for all of the subjects. Serum insulin, leptin, and lipid levels were compared between the two groups.

RESULTS

Leptin levels were significantly higher in the patient group (P = 0.009) whereas body mass index values were comparable. There was a positive correlation between leptin and body mass index among both patient (r = 0.464, P = 0.01) and control groups (r = 0.734, P = 0.0001). Total cholesterol and low-density lipoprotein (LDL) cholesterol levels were lower in VPA-treated epileptic children than the control group (P = 0.008; P = 0.003, respectively). No significant difference was determined in insulin levels between the two groups. A negative correlation was observed between plasma VPA level and total cholesterol and LDL cholesterol levels in the patient group (r = -0.380, P = 0.03, r = -0.474, P = 0.008, respectively).

CONCLUSION

This study demonstrated higher leptin levels in the patient group despite similar BMI values. Hence, it seems likely that VPA causes leptin resistance. Unlike other anti-epileptics, VPA does not produce an increase in serum cholesterol levels. On the contrary, lower levels of total and LDL cholesterol levels in VPA-receiving patients have been observed in our study.

Divergent effects of levetiracetam and tiagabine against spontaneous seizures in adult rats following neonatal hypoxia

Animal models are valuable tools for screening novel therapies for patients who suffer from epilepsy. However, a wide array of models are necessary to cover the diversity of human epilepsies. In humans, neonatal hypoxia (or hypoxia-ischemia) is one of the most common causes of epilepsy early in life. Hypoxia-induced seizures (HS) during the neonatal period can also lead to spontaneous seizures in adulthood. This phenomenon, i.e., early-life hypoxia leading to adult epilepsy - is also seen in experimental models, including rats. However, it is not known which anti-seizure medications are most effective at managing adult epilepsy resulting from neonatal HS. Here, we examined the efficacy of three anti-seizure medications against spontaneous seizures in adult rats with a history of neonatal HS: (1) phenobarbital (PHB), the oldest epilepsy medicine still in use today; (2) levetiracetam (LEV); and (3) tiagabine (TGB). Both LEV and TGB are relatively new anticonvulsant drugs that are ineffective in traditional seizure models, but strikingly effective in other models. We found that PHB and LEV decreased seizures in adult rats with a history of HS, whereas TGB exacerbated seizures. These divergent drug effects indicate that the HS model may be useful for differentiating the clinical efficacy of putative epilepsy therapies.

States of serum leptin and insulin in children with epilepsy: risk predictors of weight gain

BACKGROUND AND OBJECTIVES

Weight gain is an adverse metabolic effect in some children with epilepsy. The studies done to detect the effect of antiepileptic drugs and weight homeostatic hormones, insulin and leptin, were limited and controversial.

MATERIALS AND METHODS

We evaluated the serum leptin and insulin as predictors of weight gain in children receiving long-term treatment with valproate (VPA), carbamazepine (CBZ), lamotrigine (LTG). This study included 90 patients (treated: 70; untreated: 20). Serum lipid profile, insulin and leptin were measured.

RESULTS

BMI, serum leptin and insulin were significantly elevated in VPA compared with controls, untreated patients and those treated with CBZ, LTG and combined therapy with LTG. Girls on VPA had higher BMI and leptin levels than boys. With VPA, serum insulin was correlated with BMI (r=0.625, p<0.01), leptin (r=0.823, p<0.001), treatment duration (r=0.775, p<0.01) and VPA dose (r=0.975, p<0.0001). Serum leptin was correlated with age (r=0.980, p<0.0001), BMI (r=0.704, p<0.01), serum insulin (r=0.823, p<0.001), LDL-c (r=0.630, p<0.01), HDL-c (r=-0.880, p<0.001), treatment duration (r=0.770, p<0.01) and VPA dose (r=0.970, p<0.001). BMI is correlated with serum insulin, leptin, LDL-c (r=0.835, p<0.001) and HDL-c (r=-0.955, p<0.0001).

CONCLUSION

Hyperinsulinemia and hyperleptinemia are common with VPA and marked among epileptic children who gained weight suggesting states of insulin and leptin resistances. These alterations were not demonstrated with CBZ or LTG. The relationship between VPA, leptin and weight seems to be gender specific. Serum leptin may serve as a sensitive parameter for weight gain and reduction with intervention programs during follow-up of girls with epilepsy.

Weight change associated with the use of migraine-preventive medications

BACKGROUND

Medications administered long term, such as those used for migraine prophylaxis, are often associated with weight change as a side effect. Such effects may compromise general health status, exacerbate coexisting medical conditions, and affect medication adherence. Weight gain should be of particular concern in patients with migraine, as there is evidence that overweight and obese patients with migraine are at risk for an increased frequency and severity of migraine attacks.

OBJECTIVE

This article reviews weight-change data from recent clinical studies of migraine-preventive medications in children, adolescents, and adults with migraine.

METHODS

A PubMed search was conducted for English-language articles published between January 1970 and November 2007. Among the search terms were migraine prevention, migraine prophylaxis, migraine treatment, antidepressant drug, beta-adrenergic-receptor blockers, antiepileptic drug, anticonvulsant drug, weight gain, and weight loss. Studies that reported weight-change data (gain, loss, or neutral) were included. When available, double-blind, placebo-controlled studies were selected for review. Open-label, retrospective or prospective trials may also have been included.

RESULTS

Most of the migraine-preventive medications classified by the United States Headache Consortium as group 1 based on the high level of evidence for their efficacy--for instance, amitriptyline, propranolol, and divalproex sodium-have been associated with varying degrees of weight gain. The exceptions are timolol, which is weight neutral, and topiramate, which is associated with weight loss. Among the drugs that have been associated with weight gain, a higher incidence of weight gain was observed with amitriptyline and divalproex sodium than with propranolol.

CONCLUSION

Weight-change effects require careful consideration when selecting migraine-preventive medications, and weight should be monitored carefully over the course of any migraine treatment plan.

Leptin and insulin homeostasis in epilepsy: relation to weight adverse conditions

During managing patients with epilepsy, there is a great risk of weight changes, particularly weight gain with some antiepileptic medications. Weight gain is not only a cosmetic problem that leads to non-compliance to medications but also increases the risk for atherosclerosis and its related complications. The mechanisms underlying weight gain in epilepsy are multiple and controversial and have been attributed to the effect of epilepsy and more commonly the effect of antiepileptic medications on the central and peripheral mechanisms regulating weight homeostasis including the two main homeostatic hormones, leptin, a protein product of obesity gene secreted by adipocytes and insulin, a protein product of pancreatic beta-cells. Increased blood levels of leptin and insulin due to leptin and insulin resistance is observed in patients with epilepsy. Leptin forms an important link between weight gain, insulin resistance, epilepsy and atherosclerosis. The knowledge of the novel roles of leptin in patients with epilepsy will help identification of early markers for the related adverse weight changes, thus allowing proper characterization of suitable antiepileptic medication as initial step during management and follow up of patients.

Novel anticonvulsant drugs

Principles of complex mechanisms of action of anticonvulsants including latest reports concerning new antiepileptic drugs (AED) are considered. Different aspects of new anticonvulsant drugs (2nd generation) from preclinical and clinical testing, pharmacokinetics, and mono or combination therapy in children and adults are summarized. In the following condensed synopsis pharmacological and clinical characteristics of gabapentin (GBP), lamotrigine (LTG), levetiracetam (LEV), oxcarbazepine (OXC), pregabalin (PGB) and tiagabine (TGB) as well as topiramate (TPM) and zonisamide (ZNS) are discussed. In addition to the mechanisms of action, pharmacokinetics, interactions, indications and dosages as well as side effects are considered. Important data concerning the effect and tolerability of anticonvulsant drugs can be obtained from controlled studies. In comparison to drugs of the first generation (phenobarbital [PB], primidon [PRD], phenytoin [PHT], carbamazepine [CBZ] and valproic acid [VPA]) the potential for interactions and side effects due to enzyme induction or inhibition is reduced by most of the anticonvulsant drugs of the second generation. New anticonvulsant drugs increase the spectrum of treatment and represent further steps with regard to the optimization of an individual therapy of the epilepsies.

Weight Change and Antiepileptic Drugs

BACKGROUND

Antiepileptic drugs (AEDs) constitute a diverse class of agents with heterogeneous mechanisms of action and diverse side-effect profiles. Weight change, either gain or loss, is a common AED side effect, conferring multiple risks of additional morbidity.

REVIEW SUMMARY

The risks inherent in weight change, such as diabetes, coronary heart disease (CHD), and polycystic ovary syndrome (PCOS), may be exacerbated by the interaction of polypharmacy and comorbidities. Patients with epilepsy are more likely to be receiving multiple medications and are also more likely than the general population to suffer from morbidities related to both weight gain and weight loss. For certain patients, use of an AED associated with weight change, particularly weight loss, may be salubrious, although long-term weight change in these patients may ultimately become undesirable. Appropriate selection of an AED to minimize the risk of morbidity arising from weight change should be guided by a knowledge of patients' weight status, their comorbidities, and use of other medications. The potential for added risk in certain subpopulations, such as pediatric, elderly, and female patients, requires additional caution in selecting an AED.

CONCLUSIONS

Use of a weight-neutral AED is recommended to lessen the risk of dysfunction arising from weight change.

A randomised open-label study of tiagabine given two or three times daily in refractory epilepsy

Efficacy and tolerability of tiagabine was evaluated in patients with non-controlled partial seizures in a multicentre, open-label, parallel group study. Tiagabine was administered either two (b.i.d.) or three times daily (t.i.d.) as adjunctive therapy and titrated stepwise to a target of 40 mg/day during a 12-week, fixed-schedule titration period; this was followed by a 12-week flexible continuation period. The primary efficacy endpoint was the proportion of patients completing the fixed-schedule titration period. A total of 243 patients were randomised and received treatment, 123 to b.i.d. and 120 to t.i.d. dosing. Fewer patients in the b.i.d. (76 and 62%) than in the t.i.d. (87 and 72%) group completed the fixed-schedule titration period (OR: 0.562; 95% CI: 0.309-1.008; P=0.0532). The median percentage decrease in all types of seizure (excluding status epilepticus) during the fixed schedule titration period was 33.4% for the b.i.d. and 23.8% for the t.i.d. groups (P=0.9634; Van Elteren's test). The proportion of responders was similar for the b.i.d. and t.i.d. groups. There were no significant differences between dosage regimens in the change in median seizure rates from baseline. Adverse events were more frequent during the titration than the continuation period. Most events were mild and related to the central nervous system. Although their incidence was similar between treatment groups, severity was more frequent in the b.i.d. group. Our results suggest that during titration tiagabine is better tolerated with t.i.d. dosing, but during long-term maintenance, a t.i.d. schedule is as effective and well tolerated as b.i.d.

Valproic acid inhibits leptin secretion and reduces leptin messenger ribonucleic acid levels in adipocytes

Treatment of epilepsy or bipolar disorder with valproic acid (VPA) induces weight gain and increased serum levels for the satiety hormone, leptin, through an unidentified mechanism. In this study we tested the effects of VPA, a short-chain branched fatty acid (C8:0), on leptin biology and fatty acid metabolism in 3T3-L1 adipocytes. VPA significantly reduced leptin secretion in a dose-dependent manner. Because fatty acid accumulation has been hypothesized to block leptin secretion, we tested the effect of VPA on fatty acid metabolism. Using 14C-radiolabeled VPA, we found that the 14C was mainly incorporated into triacylglycerol. VPA did not alter lipogenesis from acetate, nor did it change the amount of intracellular free fatty acids available for triacylglycerol synthesis. Decreased leptin secretion was accompanied by a reduction in leptin mRNA, even though VPA treatment did not alter the protein levels for known transcription factors affecting leptin transcription including: CCAAT/enhancer binding protein-alpha, peroxisome proliferator-activated receptor-gamma, or steroid regulatory element binding protein 1a. VPA altered levels of leptin mRNA independent of de novo protein synthesis without affecting leptin mRNA degradation. This report demonstrates that VPA decreases leptin secretion and mRNA levels in adipocytes in vitro, suggesting that VPA therapy may be associated with altered leptin homeostasis contributing to weight gain in vivo.

Evaluation of GABA uptake in subcellular fractions of bovine frontal cortex and brainstem

GABA uptake as well as the distribution of GAT-1, GAT-2 and GAT-3 were investigated in bovine brain membrane fractions. GABA uptake was characterised by kinetic constants and IC50-values for a series of known inhibitors in subcellular fractions of frontal cortex and brainstem obtained by subsequent centrifugations on sucrose gradients. Additionally, the immunoreactivity for rGAT-1, rGAT-2 and rGAT-3 antibodies was studied in these fractions. The pharmacological profile for GABA uptake inhibition as well as results from immunoblotting indicated that GABA uptake in a selected subcellular fraction of frontal cortex (P2B) is almost exclusively due to GAT-1 whereas GABA uptake performed with a selected subcellular fraction of brainstem (P2A) in the presence of NNC 711 is mainly attributable to GAT-3.

Tiagabine in glial tumors

RATIONALE AND PURPOSE

Preliminary reports have suggested a possible 'aetiology-specific' efficacy of tiagabine (TGB) in patients with drug-resistant partial epilepsy (DRPE) related to cerebral glial tumors (GTs). This efficacy should be related to selective blocking of GAT-1 transporter by TGB. We presented our open-label, add-on TGB experience in a group of patients with GTs, compared with other symptomatic DRPEs of different aetiology.

MATERIAL AND METHODS

eleven patients with DRPE related to oligodendroglioma (six cases), astrocytoma (4) or multiform gliobastoma (1); 12 patients with DRPE related to a miscellanea of CNS lesions. TGB was added to previous AEDs, at dosage of 20-60 mg per die. Responders are defined by seizure frequency reduction >50% compared with baseline.

RESULTS

Seven patients are responders with three seizure-free (SF) in GTs group, a rate of efficacy much higher than in matching group (63.6 vs. 16.6%). Adverse events have been observed only rarely, not leading to discontinuation, in GTs group.

CONCLUSION

This preliminary observation seems to confirm the high efficacy and tolerability of TGB in DRPE related to GTs.

Special issues in the treatment of paediatric bipolar disorder

Paediatric bipolar disorder (PBD) is an increasingly diagnosed disorder affecting an estimated 1% of children and adolescents. Pharmacological treatment studies in PBD have lagged far behind those in adults. Children are currently treated with pharmacological agents, most of which have proven efficacy in adults. However, PBD is distinct from adult forms of bipolar disorder (BD) and may present unique treatment challenges. PBD often presents with rapid cycling and mixed manic states and a high co-morbidity with behavioural and attention disorders. Early onset depression may also be an early sign of PBD. Due to developmental considerations, the diagnosis of BD may be difficult to make in children without semi-structured interviews. This report discusses the special issues that should be considered when treating PBD and reviews the current literature regarding pharmacotherapy of this population. Mood stabilisers have been studied mostly in an open, uncontrolled fashion but there is growing evidence that lithium, divalproex and carbamazepine are effective in treating PBD. More recent treatment options include atypical antipsychotics and newer anticonvulsants. Other novel agents are currently being investigated in adult BD and may prove applicable to the paediatric form. Finally, based on the available data, a treatment algorithm for PBD is proposed.

Two different anticonvulsant actions of tiagabine in developing rats

PURPOSE

Our goal was to study the anticonvulsant action of tiagabine (TGB) at different levels of brain maturation in rats.

METHODS

Wistar rats in five age groups (7, 12, 18, 25, and 90 days old) were injected intraperitoneally with TGB at doses of 0.5-32 mg/kg. Thirty minutes later, motor seizures were induced by the subcutaneous adminstration of pentylenetetrazol (PTZ) in a dose of 100 mg/kg for all of the groups except the 18-day-old rat pups, which received a 90-mg/kg dose. The incidence and latency of two types of motor seizures, minimal clonic and generalized tonic-clonic seizures (GTCSs), were evaluated, and the seizure severity was scored. The time profile of TGB action at the 8-mg/kg dose was studied in the 12-and 25-day-old rats.

RESULTS

Minimal clonic seizures were reliably induced in rats 18 days old or older, and the seizures were suppressed by TGB in all of these age groups. Although TGB was very effective against this type of seizure in the 18-day-old rats, the efficacy of the drug decreased with the age of the animal. GTCSs were suppressed by TGB in the adult and 25-day-old rats, and a U-shaped dose-response curve was outlined in these two groups. The 18-and 12-day-old rat pups exhibited a selective suppression of the tonic phase of GTCSs. A mixture of these two effects was observed in the youngest group. TGB demonstrated a markedly longer action in the 12-day-old rats than in the 25-day-old rats.

CONCLUSIONS

TGB exhibits anticonvulsant action against both minimal seizures and GTCSs. Ontogenetic development of these two actions is markedly different.

Tiagabine in the treatment of epilepsy--a clinical review with a guide for the prescribing physician

Tiagabine is currently recommended mainly as add-on therapy in adults and children above 12 years with partial epilepsy not satisfactorily controlled with other antiepileptic drugs. Based on available evidence and our clinical experience, tiagabine should be used preferably in patients sharing one or more of the following additional features, (i) a history of drug-induced cutaneous adverse events; (ii) mild to moderate epilepsy allowing for a slow titration and gradual onset of anticonvulsant action over a few weeks; (iii) patients for whom it is particularly important to avoid a deterioration in cognitive performance; and, (iv) patients who failed to respond to previous treatment with sodium channel blocker agents as they may particularly benefit from the introduction of tiagabine, due to its GABAergic mechanism of action. Tiagabine can also be used successfully in other patients with refractory partial epilepsy. Tiagabine is not indicated for patients with generalized or unclassified epilepsies and for patients with severely impaired liver function.