Presynaptic antiseizure medications - basic mechanisms and clues for their rational combinations.

Among clinically highly efficient antiseizure medications (ASMs) there are modifiers of the presynaptic release machinery. Of them, levetiracetam and brivaracetam show a high affinity to the synaptic vesicle protein type 2 A (SV2A), whereas pregabalin and gabapentin are selective ligands for the α2δ1 subunits of the voltage-gated calcium channels. In this paper, we present recent progress in understanding the significance of presynaptic release machinery in the neurochemical mechanisms of epilepsy and ASMs. Furthermore, we discuss whether the knowledge of the basic mechanisms of the presynaptically acting ASMs might help establish a rational polytherapy for drug-resistant epilepsy.

A Phase 2 Randomized Controlled Trial of the Efficacy and Safety of Cannabidivarin as Add-on Therapy in Participants with Inadequately Controlled Focal Seizures.

Objective: We assessed the efficacy, safety, and tolerability of cannabidivarin (CBDV) as add-on therapy in adults with inadequately controlled focal seizures. Materials and Methods: One hundred and sixty-two participants (CBDV n=81; placebo n=81) were enrolled. After a 4-week baseline, participants titrated from 400 to 800 mg CBDV twice daily (b.i.d.) (or placebo) over 2 weeks, followed by 6 weeks stable dosing (at 800 mg b.i.d.) and a 12-day taper period. The primary endpoint was the change from baseline in focal seizure frequency during the 8-week treatment period. Secondary endpoints included additional efficacy measures relating to seizures, physician- and participant-reported outcomes, change in the use of rescue medication, cognitive assessments, and safety. Results: Median baseline focal seizure frequencies were 17-18 per 28 days in both groups, and similar reductions in frequency were observed in the CBDV (40.5%) and placebo (37.7%) groups during the treatment period (treatment ratio [% reduction] CBDV/placebo: 0.95 [4.6]; confidence interval: 0.78-1.17 [-16.7 to 21.9]; p=0.648). There were no differences between the CBDV and placebo groups for any seizure subtype. There were no significant treatment differences between CBDV and placebo groups for any of the secondary efficacy outcome measures. Overall, 59 (72.8%) of participants in the CBDV group and 39 (48.1%) in the placebo group had ≥1 treatment-emergent adverse event (AE); the 3 most common were diarrhea, nausea, and somnolence. The incidence of serious AEs was low (3.7% in the CBDV group vs. 1.2% in the placebo group). There was little or no effect of CBDV on vital signs, physical examination, or electrocardiogram findings. Elevations in serum transaminases (alanine aminotransferase or aspartate aminotransferase) to levels >3×upper limit of normal occurred in three participants taking CBDV (two discontinued as a result) and one taking placebo; however, none met the criteria for potential Hy's Law cases. Conclusion: It is likely the 40.5% seizure reduction with CBDV represents an appropriate pharmacological response in this population with focal seizures. The placebo response was, however, high, which may reflect the participants' expectations of CBDV, and a treatment difference from placebo was not observed. CBDV was generally well tolerated. Clinical Trial Registration number: NCT02365610.

Safety and tolerability of short-term preventive frovatriptan: a combined analysis.

OBJECTIVE: To assess the safety and tolerability profile of the 5-HT(1B/1D) agonist frovatriptan (Frova(R), Endo Pharmaceuticals Inc., Chadds Ford, PA, USA) when used as a 6-day regimen for the short-term prevention of menstrual migraine scheduled over multiple perimenstrual periods. BACKGROUND: Two randomized controlled trials have established the efficacy of a 6-day regimen of frovatriptan for reducing the incidence and severity of menstrual migraine over 1 to 3 perimenstrual periods; long-term data are needed to further assess the safety and tolerability profile of this regimen. METHODS: Two multinational trials were included in the analysis: Study 1 was a randomized, placebo-controlled double-blind parallel trial (3 perimenstrual periods treated) with an open-label extension (3 additional perimenstrual periods treated), and Study 2 was a long-term (12 perimenstrual periods treated over 12-15 months) open-label study. Enrolled women experienced menstrual migraine defined as predictable migraine attacks that started -2 days to +3 (Study 1) or +4 (Study 2) days relative to the first day of menses and that occurred in at least 2 out of 3 menstrual cycles. Frovatriptan or placebo was given 2 days before anticipated menstrual migraine and continued for 6 days. Adverse events, serious adverse events, vital signs, cardiovascular events, electrocardiograms, and laboratory parameters were assessed and recorded periodically and summarized using descriptive statistics. Adverse event data from Study 1 and Study 2 were compared using event rates. RESULTS: The demographic characteristics of the 2 study populations were similar: the mean age was approximately 38 years, > or =94% of participants were white, and 85% reported menstrual migraine began on days -2 to +1 of the menstrual cycle. The mean reported history of menstrual migraine was approximately 11 years. A large percentage of the respective safety populations completed each study or study period: 87% (362/416) and 88% (273/309) completed the double-blind period and open-label periods of Study 1, respectively, and 59% (308/525) completed treatment of 12 perimenstrual periods in Study 2. Major reasons for discontinuation in Study 1 included adverse events (5%, double-blind period) and "other" (10% double-blind period and 5% open-label period). In Study 2, major reasons for discontinuation included patient request (17.3%) and adverse event (10.2%). The most common treatment emergent adverse events in the double-blind period of Study 1 (placebo vs frovatriptan twice daily) were upper respiratory infection (9% vs 9%), nausea (6% vs 8%), dizziness (7% vs 7%), fatigue (4% vs 7%), dysmenorrhea (3% vs 7%), influenza (3% vs 6%), neck pain (4% vs 6%), and migraine (4% vs 4%). With the exception of migraine (which was reported using a different method in each study), prevalence rates for Studies 1 and 2 were numerically similar. The most frequently reported cardiovascular adverse events during double-blind treatment (placebo vs frovatriptan twice daily) were chest discomfort (2% and 3%), chest pain (2% and 2%), and hypertension (0 and 2%). The corresponding adverse event rates in Study 2 were 2% (chest pain), 3% (chest discomfort), and 3% (hypertension). In both studies, most adverse events were of mild or moderate intensity and their incidence numerically declined with each perimenstrual period/cycle, as did the incidence of menstrual migraine. The observed rate of intercurrent migraine in Study 2 over 12 perimenstrual periods was 1.5 per month, compared with 1.7 at baseline. There was no observable increase in the first occurrence of migraine in the 5 days following the perimenstrual period, indicating a lack of rebound headache. CONCLUSIONS: During treatment of up to 12 perimenstrual periods over a 12- to 15-month period, the safety and tolerability of frovatriptan for short-term prevention of menstrual migraine was similar to that observed with acute use of triptans. Adverse events were generally mild or moderate in severity, there was no evidence of an increased risk of cardiovascular adverse events relative to acute treatment, and rebound headache was not evident. A short-term regimen with frovatriptan presents a safe and viable treatment option for preventing predictable migraine such as menstrual migraine.

Mechanisms of action of antiepileptic drugs.

Gamma-aminobutyric acid (GABA), one of the main inhibitory neurotransmitters in the brain, interacts with three types of receptors for GABA--GABA(A), GABA(B) and GABA(C). GABA(A) receptors, associated with binding sites for benzodiazepines and barbiturates in the form of a receptor complex, control opening of the chloride channel. When GABA binds to the receptor complex, the channel is opened and chloride anions enter the neuron, which is finally hyperpolarized. GABA(B) receptors are metabotropic, linked to a cascade of second messengers whilst the physiological meaning of ionotropic GABA(C) receptors, mainly located in the retina, is generally unknown. Novel antiepileptic drugs acting selectively through the GABA-ergic system are tiagabine and vigabatrin. The former inhibits neuronal and glial uptake of GABA whilst the latter increases the synaptic concentration of GABA by inhibition of GABA-aminotransferase. Gabapentin, designed as a precursor of GABA easily entering the brain, was shown to increase brain synaptic GABA. This antiepileptic drug also decreases influx of calcium ions into neurons via a specific subunit of voltage-dependent calcium channels. Conventional antiepileptics generally inhibit sodium currents (carbamazepine, phenobarbital, phenytoin, valproate) or enhance GABA-ergic inhibition (benzodiazepines, phenobarbital, valproate). Ethosuximide, mainly controlling absences, reduces calcium currents via T-type calcium channels. Novel antiepileptic drugs, mainly associated with an inhibition of voltage-dependent sodium channels are lamotrigine and oxcarbazepine. Since glutamate-mediated excitation is involved in the generation of seizure activity, some antiepileptics are targeting glutamatergic receptors--for instance, felbamate, phenobarbital, and topiramate. Besides, they also inhibit sodium currents. Zonisamide, apparently sharing this common mechanism, also reduces the concentration of free radicals. Novel antiepileptic drugs are better tolerated by epileptic patients and practically are devoid of important pharmacokinetic drug interactions.