Can Neurontin (gabapentin) cause syncope or ventricular tachycardia?/nAn 82-year-old man is treated

Fråga: Can Neurontin (gabapentin) cause syncope or ventricular tachycardia?

An 82-year-old man is treated with Neurontin (gabapentin) 400 mg four times daily due to severe pain. He is not epileptic. He has had several episodes of syncope during the summer and during the past few weeks he has also had ventricular tachycardia.

Other drugs are Ketodur (ketobemidone) 25 mg twice daily and Plendil (felodipine) 5 mg daily.

Sammanfattning: There are case reports suggesting that gabapentin can cause syncope and ventricular arrhythmias as adverse effects. However, there is no documentation in the literature supporting this.

Svar: Gabapentin is an anticonvulsant drug used as adjunctive therapy for the treatment of partial seizures in patients with epilepsy (1). Although gabapentin is an analogue of gamma-aminobutyric acid (GABA), it is neither a GABA agonist nor antagonist and its mechanism of action is unknown. The bioavailability is dose dependent. Gabapentin is not metabolised and is excreted unchanged in the urine with a half-life of about 5-7 hours (1,2).

We could not find any documentation in Drugline, Medline or common pharmacological handbooks indicating that gabapentin, ketobemidone or felodipine can cause syncope or ventricular arrhythmias as adverse effects.

The Swedish catalogue of approved medical products (FASS) does not contain any information that gabapentin can cause syncope or affect the cardiovascular system. For ketobemidone, bradycardia is mentioned as a common (>1/100) adverse effect. Syncope and tachycardia are stated as less common (1/100-1/1000) adverse effects, due to hypotension, with felodipine treatment (1).

However, the files of SADRAC (Swedish Adverse Drug Reaction Advisory Committee) contain one report concerning tachycardia and one report concerning palpitation, both of them classified as possible, with gabapentin treatment. Following ketobemidone treatment there is one case of bradycardia and one of asystole reported. No case of syncope has been reported for gabapentin or ketobemidone. After treatment with felodipine there are three cases of syncope, two of tachycardia, three of atrial fibrillation, five of palpitation and one case of atrioventricular block reported, all of them judged as possible (3).

In WHO´s adverse reactions database Intdis, there are 15 reports of syncope with gabapentin treatment and 56 reports associated with arrhythmias, thereof two reports of ventricular arrhythmia, one of atrioventricular block, twelve of tachycardia and twelve of palpitation. However, these reports are not evaluated due to the differences of the reporting systems in the participating countries (4).

If the time relationship between this patient´s syncope and ventricular tachycardia corresponds with the drug treatment and if other possible causes have been excluded we recommend this case be reported to SADRAC (The Swedish Adverse Drug Reaction Advisory Committee).