Davis MDCH 5210 - Anticonvulsants 2006 1 Selective CNS drugs (Depressants), used to treat epilepsy. These syndromes affect about 1% of the population.
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Davis MDCH 5210 - Anticonvulsants 2006 1 Selective CNS drugs (Depressants), used to treat epilepsy. These syndromes affect about 1% of the population. One would hope to have anticonvulsants that affect pathologically altered neurons of seizure foci, which would then prevent or reduce their excessive discharge. The way that anticonvulsants work is to reduce the spread of excitation from seizure foci and prevent detonation and disruption of function of the normal neurons. The underlying pathology is not affected. Idiopathic epilepsy: No visible pathology, yet abnormal neuronal firing takes place and spreads throughout the brain. The pattern of initiation and the extent of propagation determines the type and severity of the seizure. Anticonvulsants
Davis MDCH 5210 - Anticonvulsants 2006 2 Anticonvulsant tests: Strychnine – blocks glycine receptors Bicuculline – GABA antagonist Picrotoxin – Blocks GABA Cl - ion channels Maximal electroshock (MES) Pentylene tetrazole (sc MET) Two Major Seizure classes Partial Generalized Absence Note: Generalized tonic-clonic seizures respond to the same drugs as partial seizures. Anticonvulsant tests - Major Seizure classes :
Davis MDCH 5210 - Anticonvulsants 2006 3 Classification of Seizures
Davis MDCH 5210 - Anticonvulsants 2006 4 Valproate Lamotrigine Seizures and Drugs.
Davis MDCH 5210 - Anticonvulsants 2006 5 Mechanisms
Davis MDCH 5210 - Anticonvulsants 2006 7 Na and Ca Channels
Davis MDCH 5210 - Anticonvulsants 2006 8 Drugs effective against MES seizures: Inhibitors of MES induced seizures are indicative of action against partial seizures. These compounds don’t act at the seizure focus, but prevent the spread of seizures. Mechanism of action for MES inhibitors. Alter Na + and K + ion conductances, interact with ion channels in membranes. Some have a similar mechanism of action to local anesthetics. SAR of partial seizure/MES compounds: Phenyl ring(s) are necessary (first group). Example is phenobarbital. Valproate is an exception because it works for everything. Drugs: Carbamazepine Phenytoin Phenobarbital Primidone Valproate Gabapentin Lamotrigine Zonisamide MES Seizures
Davis MDCH 5210 - Anticonvulsants 2006 9 These drugs are effective against absence seizures. These act at the seizure focus and may also prevent spread of seizure. Interaction at Ca +2 channels. May also have some general membrane protein effect, or act at GABA receptors. Clonazepam is sometimes used. Drugs: Ethosuximide Clonazepam Valproate Lamotrigine? Drugs effective against scMET seizures:
Davis MDCH 5210 - Anticonvulsants 2006 10 Valproate Lamotrigine Seizures and Drugs.
Davis MDCH 5210 - Anticonvulsants 2006 11 Barbiturates and related compounds.- Phenobarbital has been widely used. Other barbiturates have no advantages, but the phenyl-substituted barbiturates are effective. SAR is the same as for sedative/hypnotic effects. Hydantoins. Na + channels SAR-
Davis MDCH 5210 - Anticonvulsants 2006 12 Succinimides. Ca +2 channels Benzodiazepines Clonazepam and Clorazepate are good for scMET induced seizures, not so good for MES seizures. Diazepam is used for status epilepticus. SAR-2
Davis MDCH 5210 - Anticonvulsants 2006 13 Carbamazepine (Tegretol, Carbatrol) – Ineffective against Met induced seizures, but is good for mixed seizure patients in the partial group. Na + channels. Lamotrigine (Lamictal) – Na + channels. Similar to phenytoin and carbamazepine. Valproate (Depakine) – Broadest activity of all antiepileptic agents. Affect Na + channel recovery and also increases GABA levels. May stimulate synthesis or inhibit degradation. Gabapentin (Neurontin) – Promotes GABA release. Was supposed to be a GABA agonist, but it doesn’t work that way. Baclofen may also work that way. -vinyl GABA (vigabatrin), (Sabril). – Inhibits GABA transaminase. There are a number of compounds that do this. Topiramate (Topamax) - Mechanism is still unclear. Affects GABA Cl- flux similar to BDZs, but is not inhibited by Fumazenil. Not like barbiturates either. Antagonizes non- NMDA glutamate receptors. Tiagabine (Gabitril) - GABA reuptake inhibitor. Interesting SAR Zonisamide (Zonegran) - Na+ channels or Ca+2 channels. Miscellaneous/Important mechanisms of action:
Davis MDCH 5210 - Anticonvulsants 2006 14 Structures
Davis MDCH 5210 - Anticonvulsants 2006 15 Zonisamide (Zonegran) More Stuctures
Davis MDCH 5210 - Anticonvulsants 2006 16 Synthesis of Novel GABA Uptake Inhibitors. 3. Diaryloxime and Diarylvinyl Ether Derivatives of Nipecotic Acid and Guvacine as Anticonvulsant Agents 1 Lars J. S. Knutsen, Knud Erik Andersen, Jesper Lau, Behrend F. Lundt, Rodger F. Henry, Howard E. Morton, Lars N ｾ rum, Hans Petersen, Henrik Stephensen, Peter D. Suzdak, Michael D. B. Swedberg, Christian Thomsen, and Per O. Srensen J. Med. Chem.; 1999; 42(18) pp 3447 - 3462; MedChem/Drug Design
Davis MDCH 5210 - Anticonvulsants 2006 17 Model for SAR of GABA Reuptake Inhibitors. The “linker” region has been proposed to interact with a positive region of the GABA transporter. MedChem/Drug Design-2
Davis MDCH 5210 - Anticonvulsants 2006 18 Electrostatic potential calculations 52 for molecules 11, 12, and 13. The most electronegative surface is represented by the red shading (the linker is indicated by the red arrows), graduating toward the electropositive via yellow and green to blue as the most electropositive. As proposed, the oxime 12 has a less electronegative region in the linker than the vinyl ether 13; both are significantly different from the pentenyl analogue 11 of tiagabine. This is reflected in their activities as inhibitors of [ 3 H]-GABA uptake in vitro, which are 335, 41, and 14 nM, respectively. MedChem/Drug Design-3
Davis MDCH 5210 - Anticonvulsants 2006 19 A special game for pharmacy students. - Based on Letterman’s “Know Your Current Events”. Also “Know Your Cuts of Meat.” Know your seizure classes! Know your seizure inducers (particularly MES, scMET) Know your mechanisms (Na, Ca, GABA) Know your main drug structures, know your phenyl rule Know your benzodiazepines Know your principles of medicinal chemistry drug design. Summary of Anticonvulsants - AED’s