9394. Lamotrigine

Lamotrigine is a widely used anticonvulsant medication that is actively used to treat epilepsy and bipolar disorder. Given the drug's high toxicity and the need for long-term treatment, it is important to select an effective yet safe dose. An effective way to determine the appropriate dose is to measure the drug's blood levels.

Pharmacotherapeutic Group

Antiepileptic drugs.

Pharmacodynamics

Mechanism of action:

• a) Selective blockade of voltage-gated Na⁺ channels in neurons that undergo slow inactivation, resulting in inhibition of neurons with high-frequency activity without affecting the activity of normally functioning neurons;
• b) inhibition of the release and synthesis of the main excitatory neurotransmitter, glutamate, which plays an important role in the development of nociceptive responses;
• c) blockade of voltage-gated Ca²⁺ channels in neurons of the hippocampus and striatum.

Pharmacokinetics

After oral administration, lamotrigine is rapidly and completely absorbed from the gastrointestinal tract. Cmax in plasma is reached approximately 2.5 hours after administration. Plasma protein binding is 55%. The drug undergoes extensive metabolism, producing its main metabolite, N-glucuronide. The mean elimination half-life (T½) in adults is 29 hours. It is excreted by the kidneys, predominantly as a metabolite; approximately 8% of the active substance is excreted unchanged. The elimination half-life (T½) in children is shorter than in adults.

Overdose

Single doses exceeding the maximum therapeutic doses by 10–20 times have been reported.

Symptoms: syncope, headache, drowsiness, vomiting, ataxia, nystagmus, and impaired consciousness progressing to coma.

• Monitoring the drug concentration in the blood.
• Assessment of drug interactions (when other anticonvulsants that affect the blood concentration of lamotrigine are prescribed concomitantly).
• Diagnosis of overdose.
• Detection of non-compliance with the prescribed dosing regimen.
• In the presence of physiological or pathological factors affecting pharmacokinetics – age-related characteristics, liver disease, kidney disease, or gastrointestinal disorders.
• When changing the brand name or manufacturer of the medication.

• Venous blood

In order to exclude factors that may affect the test results, we recommend to follow the preparation rules: