Pharmacokinetic Interactions Between Antiseizure and Psychiatric Medications

A case of lacosamide and mirtazapine self-poisoning

Lacosamide is a relatively new antiepileptic drug that exerts its anticonvulsant effect by selectively inactivating sodium channels. Since its launch, it has been used widely for the treatment of intractable epilepsy, but there are scant data on the toxic or lethal blood concentrations. Here, we report a case of drug poisoning following simultaneous high-dose self-administration of lacosamide and mirtazapine. We developed and validated an approach that uses liquid chromatography coupled with electrospray ionization-tandem mass spectrometry to determine the concentrations of lacosamide and mirtazapine in cadaveric blood, urine and liver. Calibration curves showed good linearity (r2 > 0.995), and our method enabled repeatable and accurate quantification, with intra- and inter-assay coefficients of variation not exceeding 10.9 % and 12.8 %, respectively, for each target drug. We used the method to measure the drug concentrations in the blood of a dead victim and found a lacosamide concentration of 91.9 μg/mL and a mirtazapine concentration of 12.0 μg/mL. The blood mirtazapine concentration was in the lethal range, and that of lacosamide was about 10 times the therapeutic range. The synergistically central nervous system depressive and cardiotoxic effects of these drugs may have contributed to the cause of death. We concluded that the cause of death in this case was lacosamide and mirtazapine poisoning.

Panic disorder in epilepsy

A 51-year-old woman showed structural epilepsy following an atypical, nontraumatic intracranial hemorrhage in the right frontal area. Despite successful seizure control with lamotrigine, she developed severe morning anxiety and panic attacks, leading to agoraphobia, social withdrawal, and psychogenic nonepileptic seizures. Neuropsychiatric and psychological assessments confirmed an anxiety disorder with no significant symptoms of depression. The patient received various psychopharmacological treatments with limited success. This case report illustrates that managing panic disorder in patients with structural epilepsy requires a comprehensive treatment approach that includes pharmacotherapy and psychotherapy. Differential diagnosis and accurate treatment are crucial because of the symptom overlap between panic attacks and peri-ictal fear. Screenings instruments such as the Panic and Agoraphobia Scale (PAS) can aid in assessing anxiety-related symptoms. First-line pharmacotherapy with selective serotonin reuptake inhibitors, especially sertraline, or venlafaxine can effectively reduce panic attacks and can be recommended in patients with epilepsy. Psychotherapy, particularly cognitive-behavioral therapy, is the treatment of choice. Referral to a psychiatrist is indicated when symptoms are severe or refractory to treatment.

Comorbid epilepsy and depression—pharmacokinetic and pharmacodynamic drug interactions

Background: Major depressive disorder may be encountered in 17% of patients with epilepsy and in patients with drug-resistant epilepsy its prevalence may reach 30%. This indicates that patients with epilepsy may require antidepressant treatment.

Purpose: Both pharmacodynamic and pharmacokinetic interactions between antiepileptic (antiseizure) and antidepressant drugs have been reviewed. Also, data on the adverse effects of co-administration of antiepileptic with antidepressant drugs have been added. This article was submitted to Neuropharmacology, a section of the journal Frontiers in Pharmacology.

Methods: The review of relevant literature was confined to English-language publications in PUBMED databases. Table data show effects of antidepressants on the seizure susceptibility in experimental animals, results of pharmacodynamic interactions between antiepileptic and antidepressant drugs mainly derived from electroconvulsions in mice, as well as results concerning pharmacokinetic interactions between these drugs in clinical conditions.

Conclusion: Antidepressant drugs may exert differentiated effects upon the convulsive threshold which may differ in their acute and chronic administration. Animal data indicate that chronic administration of antidepressants could reduce (mianserin, trazodone) or potentiate the anticonvulsant activity of some antiepileptics (fluoxetine, reboxetine, venlafaxine). There are also examples of neutral interactions (milnacipran).