The relevance of monitoring lamotrigine serum concentrations in chronic pain patients.

Lamotrigine is a novel anticonvulsant initially used in epilepsy treatment. Because of its physiological properties it has subsequently been introduced in pain management and has become an interesting co-analgesic, because it inhibits release of excitatory neurotransmitters, influences different sodium, calcium en potassium channels and elevates the GABA levels. A linear relationship appears to exist between serum concentrations, drug activity and clinical outcome. However, measurement of lamotrigine serum concentrations is very useful for daily dose adjustments in order to prevent toxic reactions. In most studies describing the neuropathic pain-relieving effects of lamotrigine, a daily oral dose of 300 to 400 mg was administered. Some of our patients received 800 mg lamotrigine with better results than when 400 mg doses were used. The serum concentrations in these patients were higher but still below the so-called dangerous level of approximately 15 mg/L. Lamotrigine itself is metabolized by conjugation to form inactive metabolites. Lamotrigine serum concentrations can be influenced by the intake of other drugs metabolized by the cytrochrome P450. As good pain relief depends on adequate lamotrigine serum concentrations and dangerous side effects should be avoided, we recommend to monitor individual concentration levels in relation to lamotrigine dosage. However, skin rash is an important adverse effect of lamotrigine and is independent from plasma concentration levels.