Drug-drug interactions between antiepileptics and cannabinoids.

About 40% of patients with epilepsy are associated with drug-resistant seizures, therefore there has been a continuous search for novel treatment approaches. In experimental studies, natural and synthetic cannabimimetic compounds alone or combined with antiepileptic drugs (AEDs) have been extensively studied and cannabidiol, a naturally occurring compound, has been involved in a number of clinical trials. Areas covered: The authors have performed a literature search (PubMed database up to December 2018) for studies evaluating interactions between AEDs and cannabinoid receptor ligands in experimental models of seizures. Clinical data relate to the add-on treatment with cannabidiol. Expert opinion: WIN55,212-2 mesylate (WIN, a non-selective agonist of CB₁ and CB₂ receptors) significantly potentiated the anticonvulsant activity of various AEDs in mice. Profound neurotoxic effects accompanied combinations of WIN with conventional AEDs. Among conventional and newer AEDs, ACEA (a selective CB₁ receptor agonist) enhanced the protective action of phenobarbital and levetiracetam without accompanying adverse effects or pharmacokinetic interactions. Cannabidiol proved effective in clinical trials, reducing seizure frequency and the most frequently observed adverse effects were diarrhea, somnolence, and poor appetite. The retention rate was within 14-24% (12-14 weeks - 1 year) but it reached the level of 35% after 2 years.