In retigabine-treated patients in the pooled dataset, confusional state was reported in 9% of patients, hallucinations in 2% of patients and psychotic disorders in 1% of patients (see section 4.4). The majority of adverse reactions occurred in the first 8 weeks of treatment, and there was an apparent dose-relationship for confusional state only.

4.9 Overdose

 Symptoms and signs

There is limited experience of overdose with retigabine.

Retigabine overdoses in excess of 2,500 mg/day were reported during clinical studies. In addition to adverse reactions seen at therapeutic doses, symptoms of retigabine overdose included agitation, aggressive behaviour and irritability. There were no reported sequelae.

In a study in volunteers, cardiac arrhythmia (cardiac arrest/asystole or ventricular tachycardia) occurred in two subjects within 3 hours of receiving a single 900 mg retigabine dose. The arrhythmias spontaneously resolved, and both volunteers recovered without sequelae.

Treatment

In the event of overdose, it is recommended that the patient is given appropriate supportive therapy as clinically indicated, including electrocardiogram (ECG) monitoring. Further management should be as recommended by the national poisons centre, where available.

5. PHARMACOLOGICAL PROPERTIES

5.1 Pharmacodynamic properties

 Pharmacotherapeutic group: antiepileptics, other antiepileptics, ATC code: N03AX21.

Mechanism of action

Potassium channels are one of the voltage-gated ion channels found in neuronal cells and are important determinants of neuronal activity. In vitro studies indicate that retigabine acts primarily through opening neuronal potassium channels (KCNQ2 [Kv7.2] and KCNQ3 [Kv7.3]). This stabilises the resting membrane potential and controls the sub-threshold electrical excitability in neurons, thus preventing the initiation of epileptiform action potential bursts. Mutations in the KCNQ channels underlie several human inheritable disorders, including epilepsy (KCNQ2 and 3). The mechanism of action of retigabine on potassium channels has been well documented, however other mechanisms by which retigabine may assert an antiepileptic effect have yet to be fully elucidated.

In a range of seizure models, retigabine increased the threshold for seizure induction produced by maximal electroshock, pentylenetetrazol, picrotoxin and N-methyl-D-aspartate (NMDA). Retigabine also displayed inhibitory properties in multiple kindling models, for example, in the fully kindled state and in some cases during the kindling development. In addition, retigabine was effective in preventing status epilepticus seizures in rodents with cobalt-induced epileptogenic lesions, and inhibiting tonic extensor seizures in genetically susceptible mice. The relevance of these models to human epilepsy, however, is not known.

Pharmacodynamic effects

In rats, retigabine increased the sleep time induced by thiopental sodium from approximately 4 min to 53 min, and the propofol-induced sleep time from approximately 8 min to 12 min. There was no effect on sleep time induced by halothane or methohexital sodium. Trobalt may increase the duration of anesthesia induced by some anaesthetics (for example thiopental sodium).

Clinical efficacy of adjunctive retigabine therapy in partial