Used For

Lamotrigine is an antiepileptic drug (AED) of the phenyltriazine class that is chemically unrelated to existing AEDs. The precise mechanism of action is unknown although it has been postulated that lamotrigine inhibits voltage-sensitive sodium channels thereby stabilizing neuronal membranes and consequently modulating presynaptic transmitter release of excitatory amino acids (eg, glutamate, aspartate). Lamotrigine is 55% bound to plasma proteins and is metabolized predominantly to an inactive 2-N-glucuronide conjugate. Peak plasma concentration occurs at 1.4 to 4.8 hours following oral administration.¹ The elimination half-life varies from 12 to 70 hours. The longer half-lives are observed in patients on concomitant valproic acid therapy. Accordingly, if lamotrigine is coadministered with valproic acid, the dose of lamotrigine must be reduced to less than half the normal dosage. The most common adverse reactions are associated with the use of lamotrigine in combination with other anticonvulsants, and include dizziness, diplopia, ataxia, blurred vision, nausea and vomiting, somnolence, headache, and rash. The anticonvulsants phenytoin, phenobarbital, primidone, and carbamazepine can reduce lamotrigine levels when coadministered.² Conversely, lamotrigine can reduce levels of levetiracetam when coadministered.³ In children, investigators⁴ have found large differences in lamotrigine plasma levels in patients with improvement in seizure frequency, but patients who were seizure-free had higher lamotrigine levels than other patients in the study.

Footnotes

1. ARK Lamotrigine Assay [package insert]. Fremont, CA: ARK Diagnostic Inc;1600-0179-00 Rev 04, Feb 2017.

2. Patsalos PN, Berry DJ, Bourgeois BDF, et al. Antiepileptic drugs--best practice guidelines for therapeutic drug monitoring: A position paper by the subcommission on therapeutic drug monitoring, ILAE Commission on Therapeutic Strategies. Epilepsia. 2008 Jul;49(7):1239-1276. PubMed 18397299

3. Morris RG, Black AB, Harris AL, Batty, AB, Sallustio BC. Lamotrigine and therapeutic drug monitoring: Retrospective survey following the introduction of a routine service. Br J Clin Pharmacol. 1998 Dec;46(6):547-551. PubMed 9862243

4. Johannessen SI, Battino D, Berry DJ, et al. Therapeutic drug monitoring of the newer antiepileptic drugs. Ther Drug Monit. 2003 Jun;25(3):347-363. PubMed 12766564