Cannabidiol is the major nonpsychoactive ingredient in cannabis. Cannabidiol demonstrates a range of effects that may be therapeutically useful, including anti-seizure, antioxidant, neuroprotective, anti-inflammatory, analgesic, anti-tumor, anti-psychotic, and anti-anxiety properties. Exact mechanism of action of cannabidiol is not known, but may include effects on the orphan G-protein-coupled receptor GPR55; the transient receptor potential of vanilloid type-1 channel; the 5-HT1a receptor; and the α3 glycine receptors. GW Pharmaceuticals successfully developed the world’s first prescription medicine derived from the cannabis plant, Sativex® (buccal spray containing delta-9-tetrahydrocannabinol and cannabidiol) now approved in over 29 countries outside of the United States for the treatment of spasticity due to Multiple Sclerosis. GW Pharmaceuticals is developing Epidiolex® (a liquid formulation of pure plant-derived cannabidiol) for certain rare and severe early-onset, drug-resistant epilepsy syndromes.

Stiripentol is an anticonvulsant drug used in the treatment of epilepsy. It recently proved to increase the GABAergic transmission in vitro in an experimental model of immature rat. Clinical studies were based on the fact that STP also acts as an inhibitor of CYP3A4, CYP1A2, and CYP2C19 in vivo in epileptic patients. Side effects are largely due to the increase in plasma concentrations of other anticonvulsants and can be reduced by lowering the dose of those drugs. Nausea and vomiting are particularly noted when used in combination with sodium valproate. It appears to increase the potency of phenobarbital, primidone, phenytoin, carbamazepine, clobazam and diazepam.

Brivaracetam (UCB 34714, trade name Briviact), the 4-n-propyl analog of levetiracetam, is a racetam derivative with anticonvulsant properties. Briviact is indicated as adjunctive therapy in the treatment of partial-onset seizures in patients 16 years of age and older with epilepsy. Brivaracetam is believed to act by binding to the ubiquitous synaptic vesicle glycoprotein 2A (SV2A), like levetiracetam, but with 20-fold greater affinity. There is some evidence that racetams including levetiracetam and brivaracetam access the luminal side of recycling synaptic vesicles during vesicular endocytosis. They may reduce excitatory neurotransmitter release and enhance synaptic depression during trains of high-frequency activity, such as is believed to occur during epileptic activity.

Eslicarbazepine acetate is a third generation antiepileptic drug indicated for the treatment of partial-onset seizures. Structurally, it belongs to the dibenzazepine family and is closely related to carbamazepine and oxcarbazepine. Eslicarbazepine acetate was developed by scientists in Portugal. Its main mechanism of action is by blocking the voltage-gated sodium channel. Eslicarbazepine acetate is a pro-drug that is rapidly metabolized almost exclusively into eslicarbazepine (S-licarbazepine), the biologically active drug. It has a favorable pharmacokinetic and drug-drug interaction profile. However, it may induce the metabolism of oral contraceptives and should be used with caution in females of child-bearing age.

Perampanel (trade name Fycompa) is an antiepileptic drug developed by Eisai Co. that acts as a selective non-competitive antagonist of AMPA receptors, the major subtype of ionotropic glutamate receptors. Although the mechanism of action through which perampanel exerts its antiepileptic effect has not been fully elucidated, this agent antagonizes the AMPA subtype of the excitatory glutamate receptor found on postsynaptic neurons in the central nervous system (CNS). This antagonistic action prevents AMPA receptor activation by glutamate and results in the inhibition of neuronal excitation, repetitive neuronal firing, and the stabilization of hyper-excited neural membranes. Glutamate, the primary excitatory neurotransmitter in the CNS, plays an important role in various neurological disorders caused by neuronal hyperexcitation. The drug is currently approved, for the control of partial-onset seizures, in those of both sexes who suffer from epilepsy and who are 12 years of age and older, by the Food and Drug Administration. Perampanel is also approved for the treatment of primary generalized tonic-clonic seizures in patients with epilepsy aged 12 years and older. It is designated as a Schedule III controlled substance by the Drug Enforcement Administration. Perampanel has been studied in other clinical indications including Parkinson's disease.

Vigabatrin is an anticonvulsant chemically unrelated to other anticonvulsants. Vigabatrin prevents the catabolism of GABA by irreversibly inhibiting the enzyme GABA transaminase. It is an analog of GABA, but it is not a receptor agonist. However, vigabatrin is not a potent inhibitor of GABA-T with a Ki of 10 mM. Vigabatrin increases brain concentrations of gamma-aminobutyric acid (GABA), an inhibitory neurotransmitter in the CNS, by irreversibly inhibiting enzymes that catabolize GABA (gamma-aminobutyric acid transaminase, GABA-T). Duration of action is determined by rate of GABA-T re-synthesis. Vigabatrin may also work by suppressing repetitive neuronal firing through inhibition of voltage-sensitive sodium channels. Although administered as a racemic mixture, only the S(+) enantiomer is pharmacologically active. Vigabatrin is sold under the trade name SABRIL, it is indicated as adjunctive therapy for adults and pediatric patients 10 years of age and older with refractory complex partial seizures who have inadequately responded to several alternative treatments and for whom the potential benefits outweigh the risk of vision loss.

Lacosamide is an anticonvulsant that is FDA approved for the treatment of partial-onset seizures. The precise mechanism by which lacosamide exerts its antiepileptic effects in humans remains to be fully elucidated. In vitro electrophysiological studies have shown that lacosamide selectively enhances slow inactivation of voltage-gated sodium channels, resulting in stabilization of hyperexcitable neuronal membranes and inhibition of repetitive neuronal firing Common adverse reactions include diplopia, headache, dizziness, nausea. Patients with renal or hepatic impairment who are taking strong inhibitors of CYP3A4 and CYP2C9 may have a significant increase in exposure to Lacosamide tablets.

Rufinamide is an anti-epileptic drug that is FDA approved for the treatment of lennox-gastaut syndrome (LGS). The principal mechanism of action of rufinamide is modulation of the activity of sodium channels and, in particular, prolongation of the inactive state of the channel. Hormonal contraceptives may be less effective with rufinamide. Patients on valproate should begin at a rufinamide dose lower than 10 mg/kg per day (pediatric patients) or 400 mg per day (adults). Common adverse reactions include headache, dizziness, fatigue, somnolence, and nausea.

Pregabalin, marketed under the brand name Lyrica among others. LYRICA is indicated for: Neuropathic pain associated with diabetic peripheral neuropathy (DPN) Postherpetic neuralgia (PHN); Adjunctive therapy for adult patients with partial onset seizures; Fibromyalgia; Neuropathic pain associated with spinal cord injury. It has been shown the clinical effects of pregabalin are likely due to direct and selective interactions with α(2)δ-1 and α(2)δ-2 subunits of voltage-gated calcium channels. While pregabalin is a structural derivative of the inhibitory neurotransmitter gamma aminobutyric acid (GABA), it does not bind directly to GABAA, GABAB, or benzodiazepine receptors, does not augment GABAA responses in cultured neurons, does not alter rat brain GABA concentration or have acute effects on GABA uptake or degradation. However, in cultured neurons prolonged application of pregabalin increases the density of GABA transporter protein and increases the rate of functional GABA transport. Pregabalin does not block sodium channels, is not active at opiate receptors, and does not alter cyclooxygenase enzyme activity. It is inactive at serotonin and dopamine receptors and does not inhibit dopamine, serotonin, or noradrenaline reuptake.

Zonisamide is an antiseizure drug chemically classified as a sulfonamide and unrelated to other antiseizure agents. The precise mechanism by which zonisamide exerts its antiseizure effect is unknown, although it is believed that the drug blocks sodium and calcium channels, which leads to the suppression of neuronal hypersynchronization (i.e. convulsions). Sonisamide has also been found to potentiate dopaminergic and serotonergic neurotransmission but does not appear to potentiate syanptic activity by GABA (gamma amino butyric acid). Zonisamide binds to sodium channels and voltage sensitive calcium channels, which suppresses neuronal depolarization and hypersynchronization. Zonisamide also inhibits carbonic anhydrase to a weaker extent, but such an effect is not thought to contribute substantially to the drug's anticonvulsant activity. Zonisamide is approved in the United States, United Kingdom, and Australia for adjunctive treatment of partial seizures in adults and in Japan for both adjunctive and monotherapy for partial seizures (simple, complex, secondarily generalized), generalized (tonic, tonic-clonic (grand mal), and atypical absence) and combined seizures.