A risk-benefit assessment of vigabatrin in the treatment of neurological disorders

Behavioural abnormalities and retention rates of anti-epilepsy drugs during long-term treatment of epilepsy: a clinical perspective

Vigabatrin is among the most promising of the new anti-epilepsy drugs, but two unrelated complications have been noted in patients receiving vigabatrin for chronic refractory epilepsy. These are, transient behavioural abnormalities and falling numbers of patients continuing to take vigabatrin (decreasing retention rate) during long-term treatment. Psychotic reactions have been carefully documented both in patients receiving standard and new anti-epilepsy drugs, and in up to 6% of patients after epilepsy surgery. As many psychotic episodes are associated with a dramatic cessation of seizures (i.e. high efficacy of treatment), it is not surprising that behavioural abnormalities are more often seen in patients receiving higher, more effective doses of vigabatrin, particularly those taking more than 3 g/day. A gradual dose increase and slow withdrawal is recommended for possible prevention of behavioural abnormalities, at least in some patients. During treatment with standard anti-epilepsy drugs, approximately 50% of patients remain on randomized treatment with the same drug for several years. For oxcarbazepine, a new drug, the figure is 60%, and for vigabatrin it is about 50%. Although comparative trials are not available, the retention rate for vigabatrin does not appear to be strikingly different to that reported for conventional anti-epilepsy drugs. In summary, behavioural abnormalities and falling retention rates appear to be general features of chronic epilepsy, and are certainly not exclusively associated with the use of vigabatrin. Controlled trials are required to establish the specific contribution, if any, of vigabatrin in development of these complications of intractable epilepsy.

Screening electroencephalograms in autism spectrum disorders: evidence-based guideline

The purpose of this study was to establish guidelines for the use of screening electroencephalograms (EEGs) in autism spectrum disorders to identify subclinical epileptiform activity. MEDLINE and EMBASE were searched for relevant articles. The evidence was reviewed using the methodology of the Canadian Task Force on Preventive Health Care. A priori criteria were established for article selection and for grading the quality and strength of the evidence. Seizures are common, occurring in 20 to 30% of patients based on the majority of studies. Epileptiform EEG abnormalities are present in 10.3% to 72.4% of patients and subclinical abnormalities in 6.1% to 31%. Evidence for the effectiveness of anticonvulsants and corticosteroids in reducing seizures and/or autistic symptoms is based primarily on case series and case reports, with only one published randomized trial. There is currently insufficient evidence to recommend for or against the use of screening EEGs in autistic patients. Given the frequency of seizure disorders in this patient population, a high index of clinical suspicion should be maintained for subtle symptoms of seizures.

Therapeutics in pediatric epilepsy, Part 1: The new antiepileptic drugs and the ketogenic diet

Epilepsy is one of the most common and challenging neurologic disorders affecting children. Although various modalities exist to treat pediatric-onset seizures, seizures in 25% of children who are diagnosed as having epilepsy remain refractory to available therapies. Of the 8 new antiepileptic drugs (AEDs) (felbamate, gabapentin, lamotrigine, topiramate, tiagabine, levetiracetam, oxcarbazepine, and zonisamide), all but 2 (zonisamide and levetiracetam) have received Food and Drug Administration approval for adjunctive use in the pediatric population. However, most of the new AEDs used in adults have also been used in children, beyond the AEDs' approved indications. The ultimate goal of patient management is to choose the therapeutic option that provides the best chance of improving the patient's quality of life. Issues that relate to treatment choice include the likelihood of seizure recurrence, type and severity of seizures, available AED efficacies and toxicities, need for hematologic monitoring, ease of dosing, underlying medical conditions, medication interactions, urgency of initiating therapy, and cost. In this review, we discuss these issues for each of the 8 new AEDs; we also discuss the ketogenic diet and briefly review the older AEDs. Knowledge of the available AEDs will enable the practitioner to choose the best drug or drugs for individual patients.

The potential for vigabatrin-induced intramyelinic edema in humans

PURPOSE

Vigabatrin (Sabril, Hoechst Marion Roussel) is an antiepilepsy drug (AED) presently marketed in 64 countries for the treatment of partial and secondarily generalized seizures. Vigabatrin (VGB) is marketed in a subset of these countries for the treatment of infantile spasms. Clinical experience in humans has shown that VGB provides effective seizure control with a wide margin of safety. However, animal toxicity studies raised concern when prolonged administration of VGB was shown to induce intramyelinic edema (IME) in some laboratory animal species.

METHODS

Animal and human data were reviewed with respect to the potential for VGB-induced IME. Surveillance of patients receiving VGB in clinical trials or by prescription has been conducted for >15 years to identify patients developing clinical abnormalities that might be IME related.

RESULTS

The histologic lesions of VGB-induced IME in animals are reliably reproduced and correlate with changes in multimodality evoked potentials (EPs) and magnetic resonance imaging (MRI). Numerous studies of the effects of VGB on EP and MRI in epilepsy patients have demonstrated no clear-cut IME-related changes in these modalities. Additionally, autopsy and surgical brain samples from VGB-treated patients have been scrutinized for potential IME histopathology. In an estimated 350,000 patient-years of VGB exposure (approximately 175,000 patients exposed for 2 years at an average dose of 2 g/day), no definite case of VGB-induced IME has been identified.

CONCLUSIONS

Comprehensive review of a variety of sources of data failed to identify any definite case of IME in humans treated with VGB.

Vigabatrin in the treatment of infantile spasms

Infantile spasms (IS) have been conventionally treated with adrenocorticotropic hormone (ACTH), which is often associated with significant side effects. This study assessed the efficacy of vigabatrin (VGB) as an alternative in the treatment of IS and compared the efficacy of VGB in symptomatic vs cryptogenic patients. The study retrospectively reviewed 25 infants with IS (19 symptomatic, six cryptogenic) who were treated with VGB. Of the symptomatic group, 13 (68.4%) of 19 had clinical improvement, and 15 (78.9%) had electroencephalographic improvement. Three (50%) of six in the cryptogenic group had clinical improvement, and two (33%) had electroencephalographic improvement. Overall, three patients demonstrated clinical spasm control but electroencephalographic deterioration or persistence of hypsarrhythmia coupled with further cognitive decline. Four of the six partial clinical responders had deterioration of spasms with additional VGB dosage increases. VGB is comparable with ACTH in effectiveness for treatment of symptomatic IS. Higher doses of VGB may sometimes cause deterioration rather than further improvement, and therefore an optimum dosage of VGB needs to be titrated for every patient. Persistent electroencephalographic abnormalities and even electroencephalographic deterioration despite clinical control have been observed with VGB treatment; electroencephalographic monitoring during VGB treatment is recommended.

Obstructive sleep apnoea following rapid weight gain secondary to treatment with vigabatrin (Sabril)

A case of a patient with medically intractable epilepsy, who developed obstructive sleep apnoea (OSA), and an increase in seizure frequency, as a consequence of weight gain following treatment with vigabatrin is described. The relationship between exacerbation of epilepsy and sleep disruption secondary to OSA is discussed. Recommendations regarding the choice of anticonvulsants in patients at risk of developing OSA are made.

Utility of the lethargic (lh/lh) mouse model of absence seizures in predicting the effects of lamotrigine, vigabatrin, tiagabine, gabapentin, and topiramate against human absence seizures

PURPOSE

Traditional methods of preclinical screening have predicted the effects of a putative antiepileptic drug (AED) against human absence seizures by testing its efficacy against clonic seizures in the high-dose pentylenetetrazole (PTZ) model. This high-dose PTZ model correctly predicted the efficacy of ethosuximide (ESM), benzodiazepines, and valproate (VPA) and the lack of efficacy of phenytoin (PHT) and carbamazepine (CBZ). However, the high-dose PTZ model erred in predictions for (a) phenobarbital (PB) (PTZ: efficacy; human: nonefficacy); (b) lamotrigine (LTG) (PTZ: nonefficacy; human: efficacy); (c) vigabatrin (VGB) (PTZ: nonefficacy; human: proabsence effect); and (d) tiagabine (TGB) (PTZ: efficacy; human: possible proabsence). It also appears to have erred in predictions for gabapentin (GBP) (PTZ: efficacy) and topiramate (TPM) (PTZ: efficacy). Because the lh/lh genetic model of absence seizures correctly predicted effects of ESM, clonazepam, VPA, PHT, CBZ, and PB against human absence seizures, we performed this study to test the predictive utility of the lh/lh model for LTG, VGB, TGB, GBP, and TPM.

METHODS

Bipolar recording electrodes were implanted bilaterally into frontal neocortex of 8-week-old male lh/lh mice. With the exception of VGB, vehicle or drugs were administered intraperitoneally (i.p.) on alternating days, and an EEG was used to record effects on seizure frequency. With VGB, vehicle was administered i.p. on day 1, and gradually increasing doses of VGB were administered on successive days. Drug and vehicle effects were compared in corresponding 15-min epochs of the 150-min period after administration.

RESULTS

LTG (4.8-144 micromol/kg) significantly (p < 0.04) reduced seizure frequency (by 65%) compared with vehicle. In contrast, VGB (0.35-11 mmol/kg) and TGB (0.27-27 micromol/kg) significantly increased seizure frequency (300-700%) and seizure duration (1,700-1,800%; p < 0.001). GBP (18 micromol/kg to 1.8 mmol/kg) and TPM (8.9-295 micromol/kg) had no significant effect on seizure frequency.

CONCLUSIONS

In contrast to the high-dose PTZ model, the lh/lh model correctly predicted the antiabsence effect of LTG, the possible proabsence effects of VGB and TGB, and the lack of effect of GBP and TPM. The lh/lh model appears to be superior to the high-dose PTZ model in predicting efficacy of putative AEDs against human absence seizures.

Vigabatrin-induced gingival overgrowth

Vigabatrin is a relatively new medication used in the treatment of epilepsia. The present report concerns the use of vigabatrin by a 19-year-old woman. The patient manifested marked gingival overgrowth compatible clinically and histologically with the overgrowth induced by phenytoin, cyclosporine and calcium channel blockers. This is the 1st report of vigabatrin-induced gingival overgrowth. Clinicians should be aware of similar lesions in patients using new anticonvulsants.

Alteration of cardiac function in patients with temporal lobe epilepsy: different roles of EEG-ECG monitoring and spectral analysis of RR variability

PURPOSE

Because several reports have described the relation between epilepsy and cardiac arrhythmias and suggest that changes in autonomic neural control of the heart could be involved in the pathogenesis of sudden unexplained death in patients with epilepsy, the aim of this study was to evaluate cardiac function in patients with temporal lobe epilepsy.

METHODS

Sixty-five patients with epilepsy were evaluated by simultaneous ambulatory 24-h EEG-ECG monitoring, and in 30 of these, power spectral analysis of relative-risk (RR) variability also was carried out, both in the supine position and in a passive tilt position at 60 degrees. The power spectrum of RR variability, the two major spectral components detectable at low frequency (LF) and at high frequency (HF), respectively, and the LF/HF ratio were calculated.

RESULTS

By EEG-ECG monitoring, we recorded six partial seizures, and in four cases, discharges were associated with sinus tachycardia. However, interictally the occurrence of ventricular and supraventricular arrhythmias was not different from that in normal subjects. The spectral analysis of RR variability, on the other hand, demonstrated in patients with epilepsy a significant decrease in the total RR variability and in both of its components (LF and HF) in the supine position, and of the LF/HF ratio in orthostatic position.

CONCLUSIONS

These findings suggest that the spectral analysis of RR variability may detect disorders of autonomic cardiac control in patients with epilepsy, even in the absence of abnormal findings during ECG monitoring. This alteration, which is more severe in cases with right EEG focus, could play a role in the pathogenesis of cardiac arrhythmias.

Concurrent illnesses in adults with childhood-onset epilepsy: a population-based 35-year follow-up study

PURPOSE

To ascertain the occurrence of concurrent illnesses in adults with epilepsy since childhood.

METHOD

After a mean follow-up of 35 years of a prospective, population-based long-term followed patient cohort with epilepsy since childhood, comorbidity was examined in 176 surviving (100 of them with epilepsy only) and 44 dead patients and in random and employee controls.

RESULTS

Somatic comorbidity varied from 84 to 95% in patients and from 67 to 74% in controls. No significantly increased risk of somatic diseases could be shown. Psychosomatic disorders were associated in 46-74% of patients and in 42-75% of controls, and psychiatric disorders were associated in 11-23% of patients and in 7% of controls. As compared with random controls, patients with epilepsy had only a 4.0- to 4.2-fold risk of psychiatric disorders or of combinations of somatic, psychosomatic, and/or psychiatric disorders. Patients received psychotropic drugs 8.6 times more frequently than employee controls. The risk for psychiatric and psychosomatic disorders was higher than expected in patients with childhood-onset epilepsy, regardless of whether or not they were still receiving antiepileptic drugs (AEDs).

CONCLUSION

Epilepsy per se, but not AEDs, has an apparent association with the occurrence of psychiatric and psychosomatic disorders. Risk for somatic comorbidity is not increased.