Mechanism of action of antiepileptic and antimyoclonic drugs. 1995

M R Pranzatelli, and N S Nadi
Department of Pediatrics, George Washington University, Washington, DC 20010, USA.

Most drugs used to treat myoclonus are also antiepileptic. The main drugs are the benzodiazepines, valproate, and barbituates. Advances in the understanding of antiepileptic drug mechanisms of action have revealed two main patterns: increasing inhibition either through GABA or glycine, or decreasing excitation due to glutamate. Anticonvulsants such as the benzodiazepines, barbiturates, vigabatrin, tiagabine, or progabide act through GABA. New prototype anticonvulsants such as dizocilpine and remacemide target glutamate receptors or associated ion channels. For some antimyoclonic drugs such as piracetam, many effects are reported but no mechanism of action has been established. Many newer anticonvulsants have not been tested in human myoclonic disorders but efficacy against PTZ-induced seizures suggests antimyoclonic activity. Our ability to improve the treatment of myoclonus requires greater knowledge of the molecular mechanisms of myoclonus and more exact delineation of its relation to epilepsy. Better drugs also will result from refinements from prototype drugs and new concepts about brain function. Most of the discussion has been focused on the use of drugs as symptomatic treatment, but drugs such as glutamate blockers are already having a role in the treatment of degenerative neurological disorders, an important cause of some myoclonic disorders. It also may be possible to improve treatment by focusing on selective regional effects of drugs or drug delivery. The CNS penetration of drugs is often no uniform. For many antimyoclonic and antiepileptic drugs, regional studies have not been performed, especially in humans. Lack of efficacy could therefore be due to lack of drug delivery to myoclonic generators or suppression structures. It is conceivable that drug effects in different brain regions also may be opposing, such as in forebrain and hindbrain structures. Stimulation of the same receptor subtype may have different implications for myoclonus if the sites are pre- or postsynaptically located (as in 5-HTIA sites), or predominantly cerebellar versus hippocampal (as in BDZ I vs II sites). Molecular genetic abnormalities in neurological disease may affect neurotransmission and the action of drug either directly at the receptor site or in other ways such as transduction, translation, or expression. Further insights into these abnormalities may provide new targets for pharmacotherapy. Most antiepileptic and antimyoclonic drugs developed to date have aimed at broad-spectrum treatment of the symptoms, rather than treatment of regional problems such as in the forebrain or the hindbrain. Because of this, the currently available drugs have broad side effects such as cognitive impairment, tremors, teratogenicity, etc. To develop more region-specific and more efficacious drugs, we need to develop a better understanding of local central nervous system problems in myoclonus and epilepsy. The development and application of molecular biological techniques have increased our knowledge of receptors and transporters immensely. It is conceivable that in the near future we will be able to determine whether small mutations affect the structure and function of these molecules. In addition, the glimpses into the process of cell death and sprouting by remaining neurons in the epileptic brain, and perhaps the myoclonic brain, raise the possibility of designing regionally oriented drugs with greater efficacy and fewer side effects. The current developments in the understanding of the central neurons should allow for the development of exciting new pharmacotherapies in the future.

UI MeSH Term Description Entries
D004831 Epilepsies, Myoclonic A clinically diverse group of epilepsy syndromes characterized either by myoclonic seizures or by myoclonus in association with other seizure types. Myoclonic epilepsy syndromes are divided into three subtypes based on etiology: familial, cryptogenic, and symptomatic. Idiopathic Myoclonic Epilepsy,Myoclonic Absence Epilepsy,Myoclonic Encephalopathy,Myoclonic Epilepsy,Symptomatic Myoclonic Epilepsy,Benign Infantile Myoclonic Epilepsy,Cryptogenic Myoclonic Epilepsy,Doose Syndrome,Dravet Syndrome,Early Childhood Epilepsy, Myoclonic,Early Childhood, Myoclonic Epilepsy,Encephalopathy, Myoclonic,Epilepsy, Early Childhood, Myoclonic,Epilepsy, Myoclonic, Early Childhood,Epilepsy, Myoclonic, Infantile,Epilepsy, Myoclonic, Infantile, Benign,Epilepsy, Myoclonic, Infantile, Severe,Epilepsy, Myoclonus,Infantile Severe Myoclonic Epilepsy,Myoclonic Astatic Epilepsy,Myoclonic Epilepsy, Benign Infantile,Myoclonic Epilepsy, Early Childhood,Myoclonic Epilepsy, Infantile,Myoclonic Epilepsy, Infantile, Benign,Myoclonic Epilepsy, Infantile, Severe,Myoclonic Epilepsy, Severe Infantile,Myoclonic Epilepsy, Severe, Of Infancy,Myoclonic Seizure Disorder,Severe Infantile Myoclonic Epilepsy,Severe Myoclonic Epilepsy Of Infancy,Severe Myoclonic Epilepsy, Infantile,Astatic Epilepsies, Myoclonic,Astatic Epilepsy, Myoclonic,Cryptogenic Myoclonic Epilepsies,Dravet Syndromes,Encephalopathies, Myoclonic,Epilepsies, Cryptogenic Myoclonic,Epilepsies, Idiopathic Myoclonic,Epilepsies, Infantile Myoclonic,Epilepsies, Myoclonic Absence,Epilepsies, Myoclonic Astatic,Epilepsies, Symptomatic Myoclonic,Epilepsy, Cryptogenic Myoclonic,Epilepsy, Idiopathic Myoclonic,Epilepsy, Infantile Myoclonic,Epilepsy, Myoclonic,Epilepsy, Myoclonic Absence,Epilepsy, Myoclonic Astatic,Epilepsy, Symptomatic Myoclonic,Idiopathic Myoclonic Epilepsies,Infantile Myoclonic Epilepsies,Infantile Myoclonic Epilepsy,Myoclonic Absence Epilepsies,Myoclonic Astatic Epilepsies,Myoclonic Encephalopathies,Myoclonic Epilepsies,Myoclonic Epilepsies, Cryptogenic,Myoclonic Epilepsies, Idiopathic,Myoclonic Epilepsies, Infantile,Myoclonic Epilepsies, Symptomatic,Myoclonic Epilepsy, Cryptogenic,Myoclonic Epilepsy, Idiopathic,Myoclonic Epilepsy, Symptomatic,Myoclonic Seizure Disorders,Myoclonus Epilepsies,Myoclonus Epilepsy,Seizure Disorder, Myoclonic,Seizure Disorders, Myoclonic,Symptomatic Myoclonic Epilepsies
D005680 gamma-Aminobutyric Acid The most common inhibitory neurotransmitter in the central nervous system. 4-Aminobutyric Acid,GABA,4-Aminobutanoic Acid,Aminalon,Aminalone,Gammalon,Lithium GABA,gamma-Aminobutyric Acid, Calcium Salt (2:1),gamma-Aminobutyric Acid, Hydrochloride,gamma-Aminobutyric Acid, Monolithium Salt,gamma-Aminobutyric Acid, Monosodium Salt,gamma-Aminobutyric Acid, Zinc Salt (2:1),4 Aminobutanoic Acid,4 Aminobutyric Acid,Acid, Hydrochloride gamma-Aminobutyric,GABA, Lithium,Hydrochloride gamma-Aminobutyric Acid,gamma Aminobutyric Acid,gamma Aminobutyric Acid, Hydrochloride,gamma Aminobutyric Acid, Monolithium Salt,gamma Aminobutyric Acid, Monosodium Salt
D006801 Humans Members of the species Homo sapiens. Homo sapiens,Man (Taxonomy),Human,Man, Modern,Modern Man
D000818 Animals Unicellular or multicellular, heterotrophic organisms, that have sensation and the power of voluntary movement. Under the older five kingdom paradigm, Animalia was one of the kingdoms. Under the modern three domain model, Animalia represents one of the many groups in the domain EUKARYOTA. Animal,Metazoa,Animalia
D000927 Anticonvulsants Drugs used to prevent SEIZURES or reduce their severity. Anticonvulsant,Anticonvulsant Drug,Anticonvulsive Agent,Anticonvulsive Drug,Antiepileptic,Antiepileptic Agent,Antiepileptic Agents,Antiepileptic Drug,Anticonvulsant Drugs,Anticonvulsive Agents,Anticonvulsive Drugs,Antiepileptic Drugs,Antiepileptics,Agent, Anticonvulsive,Agent, Antiepileptic,Agents, Anticonvulsive,Agents, Antiepileptic,Drug, Anticonvulsant,Drug, Anticonvulsive,Drug, Antiepileptic,Drugs, Anticonvulsant,Drugs, Anticonvulsive,Drugs, Antiepileptic
D001463 Barbiturates A class of chemicals derived from barbituric acid or thiobarbituric acid. Many of these are GABA MODULATORS used as HYPNOTICS AND SEDATIVES, as ANESTHETICS, or as ANTICONVULSANTS.
D014635 Valproic Acid A fatty acid with anticonvulsant and anti-manic properties that is used in the treatment of EPILEPSY and BIPOLAR DISORDER. The mechanisms of its therapeutic actions are not well understood. It may act by increasing GAMMA-AMINOBUTYRIC ACID levels in the brain or by altering the properties of VOLTAGE-GATED SODIUM CHANNELS. Dipropyl Acetate,Divalproex,Sodium Valproate,2-Propylpentanoic Acid,Calcium Valproate,Convulsofin,Depakene,Depakine,Depakote,Divalproex Sodium,Ergenyl,Magnesium Valproate,Propylisopropylacetic Acid,Semisodium Valproate,Valproate,Valproate Calcium,Valproate Sodium,Valproic Acid, Sodium Salt (2:1),Vupral,2 Propylpentanoic Acid
D016194 Receptors, N-Methyl-D-Aspartate A class of ionotropic glutamate receptors characterized by affinity for N-methyl-D-aspartate. NMDA receptors have an allosteric binding site for glycine which must be occupied for the channel to open efficiently and a site within the channel itself to which magnesium ions bind in a voltage-dependent manner. The positive voltage dependence of channel conductance and the high permeability of the conducting channel to calcium ions (as well as to monovalent cations) are important in excitotoxicity and neuronal plasticity. N-Methyl-D-Aspartate Receptor,N-Methyl-D-Aspartate Receptors,NMDA Receptor,NMDA Receptor-Ionophore Complex,NMDA Receptors,Receptors, NMDA,N-Methylaspartate Receptors,Receptors, N-Methylaspartate,N Methyl D Aspartate Receptor,N Methyl D Aspartate Receptors,N Methylaspartate Receptors,NMDA Receptor Ionophore Complex,Receptor, N-Methyl-D-Aspartate,Receptor, NMDA,Receptors, N Methyl D Aspartate,Receptors, N Methylaspartate

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