Myoclonus gabapentin

Gabapentin-induced myoclonus may be more common than initially thought. In a retrospective survey, 13 of 104 consecutive patients developed myoclonus at gabapentin dosages of 800-3200 mg/day (11). Six of the patients had severe chronic static encephalopathy. Three had focal myoclonus, contralateral to the epileptic focus, and two had exacerbation of pre-existent myoclonus. In aU cases the myoclonus was mild and did not interfere with daily activities. The fact that in three patients the electroencephalogram did not show epileptiform discharges suggests that, at least in some cases, the myoclonus is non-epileptic in nature. 

Asconape J, Diedrich A, DellaBadia J. Myoclonus associated with the use of gabapentin. Epilepsia 2000 41(4) 479-81. 

Gabapentin has been used to treat morphine-induced myoclonus in a 54-year-old patient with gallbladder cancer (13). Effective pain control was maintained with morphine 300 mg, but after 24 hours the patient developed generalized muscular movements while asleep. Gabapentin 300 mg bd produced complete resolution of symptoms after 12 hours. In another case gabapentin 600 mg/day was used to treat a 1-month history of spontaneous jerking of both wrists after an increase in the dose of morphine to 120 mg/day the myoclonus disappeared over the next 24 hours (8,13). 

Mercadante S, Villari P, Fulfaro F. Gabapentin for opioid-related myoclonus in cancer patients. Support Care Cancer 2001 9(3) 205-6. 

Adverse effects of gabapentin are uncommon and not serious. The CNS effects include mild to moderate sedation, fatigue, ataxia, headache, dizziness, and diplopia. Gabapentin may exacerbate myoclonus, but the effect is mild and does not require discontinuance of the drug (53,74). It has been associated with the development of neuropsychiatric adverse events in children. 

Observational studies The usefulness of gabapentin in combination with opioids in 24 Japanese patients with neuropathic cancer pain has been assessed in an open prospective study [155 ]. Gabapentin was added to opioid therapy in an initial dose of 200 mg/day titrated to a maximum dose of 2400 mg/day over 15 days. Gabapentin reduced the score on a pain scale, but the reduction was of minimal clinical benefit. Four patients withdrew because of adverse events headache, myoclonus, heartburn, and an attack of bronchial asthma). Only a few patients reported somnolence or dizziness, and these symptoms did not require drug withdrawal. 

Gabapentin-induced myoclonus occurred in an elderly patient with no other medical conditions that could have caused it [113 ]. 

In a retrospective study in 162 patients with epilepsy taking gabapentin, pre-existing myoclonus was worsened in two cases within 2 weeks of starting gabapentin in another case it occurred de novo [116. Withdrawal of gabapentin or clonazepam add-on treatment resulted in resolution of myoclonus with no serious sequelae in aU three cases. 

A 46-year-old woman with a 6-year history of diabetes mellitus and previously normal renal function developed anuria, hearing loss, myoclonus, and confusion with hallucinations. She was taking lisinopril, hydrochlorothiazide, furose-mide, atorvastatin, omeprazole, salmeterol/fluti-casone and salbutamol by inhalation, metformin, insulin, oxycodone, alprazolam, ven-lafaxine, and gabapentin 300 mg tds. The gabapentin blood concentration was 17.6 mg/1. All her symptoms improved after one session of hemodialysis and had resolved at the time of discharge 4 days later. 

This patient previously had similar reversible confusion and myoclonus while taking gabapentin 300 mg tds. 

Ege F, Kogak Y, Titiz AP, Oztiirk SM, OztUrk S, Ozbakir S. Gabapentin-induced myoclonus case report. Mov Disord 2008 23(13) 1947-8. 

Koide Y, Ikeda H, Inoue Y. Development or worsening of myoclonus associated with gabapentin therapy. Rinsho Shinkeigaku 2009 49(6) 342-7. 

Healy DG, Ingle GT, Brown P. Pregaba-lin-and gabapentin-associated myoclonus in a patient with chronic renal failure. Mov Disord 2009 24(13) 2028-9. 

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