Published: November 2009

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Lamotrigine - reduced dose required in patients taking sodium valproate

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Prescriber Update 30(14): 24
November 2009

Prescribers are reminded to adhere to the recommended dose guidelines when prescribing lamotrigine to patients already taking sodium valproate. Adhering to these dosing guidelines reduces the risk of serious skin reactions.

The CARM database contains reports of toxic epidermal necrolysis (TEN) and Stevens Johnson’s syndrome (SJS) in patients taking concomitant lamotrigine and sodium valproate. It has been identified that risk factors included exceeding the recommended starting dose of lamotrigine or the rate of dose escalation.

The incidence of serious skin reactions (including TEN and SJS) in clinical trials using recommended lamotrigine dosing is approximately 1 in 500 epilepsy patients and 1 in 1000 patients with bipolar disorder. The incidence of serious skin reactions is greater in children with estimates ranging from 1 in 300 to 1 in 100 children. Serious skin reactions generally occur within 8 weeks of commencing lamotrigine therapy; the risk is increased by high initial doses of lamotrigine, exceeding recommended doses, rapid dose escalation and concomitant use of sodium valproate.

Lamotrigine is approved in New Zealand as adjunctive therapy in adults and children with epilepsy, and for the prevention of mood disorders in adults with bipolar disorder. In adult patients already taking sodium valproate the starting dose of lamotrigine is 12.5mg/day (or 25mg on alternate days) for 14 days, increased to 25mg/day for a further 14 days. The dose of lamotrigine can thereafter be increased by 25–50mg/day every 7 –14 days.

Further information on the use of lamotrigine and dose regimens for children can be found in data sheet on the Medsafe website:
www.medsafe.govt.nz/Medicines/infoSearch.asp