Anticonvulsant or Antiepileptic Drugs. Munir Gharaibeh, MD, PhD, MHPE School of Medicine, The University of Jordan March, 2018

Transcription

1 Anticonvulsant or Antiepileptic Drugs Munir Gharaibeh, MD, PhD, MHPE School of Medicine, The University of Jordan March, 2018

2 Anticonvulsant or Antiepileptic Drugs Seizure: an abnormal electrical activity, not necessarily to result in a convulsion. Convulsion (Fit): the attack itself. Epilepsy: a disease characterized by recurrent attacks of convulsions.

3 Neuronal Mechanisms involved in Seizures ÚSuppression of Inhibition Onset ÚPost-tetanic Potentiation Spread and Maintenance ÚReinstitution of Inhibition---Termination ÚPattern related to anatomical site of the focus. 3

4 Pathophysiological Conditions Enhancing Convulsions Ú Low PO2 Ú High ph Ú Increased Intracranial Pressure Ú Low Ca++ Ú Low Glucose Ú Overhydration Ú Fatigue Ú Emotional State 4

5 Causes of Convulsions Ú Poisons Ú Trauma Ú Infection Ú Space Occupying Lesions Ú Fever Ú Drugs Ú Epilepsies 5

6 Classification of Epilepsies ÚGrand Mal or Major Epilepsy or Tonic- Clonic Epilepsy: Ú Ú Ú Ú Ú Aura Cry-Loss of consciousness Tonic Phase: Rigid violent muscle contraction with limbs fixed. Clonic Phase: Repetitive muscle jerks Post-ictal depression and incotinence 6

7 Classification of Epilepsies Petit Mal or Minor Epilepsy or Absence States: Psychomotor Epilepsy: Ú Ú Ú Automatic movements Clouded dreamy feeling Aggressiveness 7

8 Classification of Epilepsies ÚStatus Epilepticus ÚParietal Lobe Epilepsy ÚInfantile Myospasm Úetc... 8

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11 Provocative Procedures ÚPentylene tetrazole "Metrazole" ÚHyperventilation ÚPhotic stimulation - Flicker Fusion 11

12 Principles of Epilepsy Treatment Ú Seizures are self-limiting. Ú One drug at a time( Monotherapy): Lower incidence of adverse reactions. Avoidance of drug interactions. Improved patient compliance. Lower medication cost. Ú Start with a small dose. Ú Monitor serum level. 12

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15 Barbiturates ÚPhenobarbital ÚMephobarbital ÚMethabarbital ÚPrimidone 15

16 Barbiturates Ú Oldest but still used. Ú Relatively safe, but sedating. Ú Effective in Grand mal and partial seizures. Ú Might worsen patients with other types. Ú Bind to GABA receptor, to prolong opening of Clchannels. Ú Also, at high doses, block Na+ and Ca++ channels (L and N type). Ú Also block Glutamate receptors. 16

17 Adverse Effects: Ú Ú Ú Ú Ú Ú Barbiturates Sedation Allergies Anemia Drug Interactions Enzyme Induction Withdrawal!! Additive to CNS depressants. 17

18 Phenytoin(1938) ÚGeneralized tonic - clonic seizures ÚPartial seizures with complex symptomatology ÚAntipsychotic ÚAntiarrhythmic ÚMany others ÚRevolutionary 18

19 Mechanism of Action: Phenytoin Acts on several physiologic systems. Major action is sodium channel blockade, arising from preferential binding to and prolongation of the inactivated state of the Na + channel. Also, inhibits Ca++ influx, membrane potential, as well as, the concentrations of amino acids, NE, ACh, and GABA. Blocks sustained high-frequency repetitive firing of action potentials. 19

20 ÚPharmacokinetics: Slow absorption 90% bound Metabolized: Interactions: Phenytoin Zero order in high doses used in epilepsy, so, no SSL achieved. Protein binding. Enzyme induction. 20

21 Phenytoin Adverse Effects: Ú Skin rashes, fever Ú Blood: megaloblastic anemia, agranulocytosis, lymphadenopathy. Ú Gingival hyperplasia (50%) Ú Hirsutism Ú "Hydantoin Facies" Ú Peripheral neuropathy Ú Cerebellar degeneration Ú Teratogenic Folate Deficiency 21

22 Phenytoin Overdose: Ú Nystagmus, Ú Ataxia, Ú Vertigo, Ú Diplopia Ú Loss of consciousness. 22

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24 Carbamazepine Ú Partial seizures Ú Generalized tonic - clonic Ú Not for petit mal Ú Initially marketed for Trigeminal Neuralgia. Ú Bipolar mood disorders, it is a tricyclic compound. Ú Peripheral Neuropathy Ú Migraine etc 24

25 Carbamazepine Mechanism of Action: Like phenytoin, blocks Na+ channels. 25

26 Carbamazepine ÚSlow and erratic absorption ÚT½ hr. ÚInduces liver enzymes = Autoinduction. ÚInteractions. ÚBlood monitoring is necessary. 26

27 Carbamazepine Adverse Effects: Vertigo, Ataxia, Diplopia appear early. ÚDrowsiness, nausea, headache, dizziness. ÚTolerance develops to the above effects. ÚSkin rashes, fever, hepatosplenomegaly, lymphadenopathy. ÚBlood dyscrasias: leukopenia, aplastic anemia, and agranulocytosis. 27

28 Oxacarbazepine. ÚLess capacity to induce enzymes. ÚT½ 1-2hr. ÚMay be safer. 28

29 Vigabatrin ÚGABA-Transaminase irreversible inhibitor, which breaks down GABA in the brain. ÚRenal elimination. ÚPartial seizures Not for absence or myoclonic ÚWell tolerated: drowsiness, dizziness, weight gain, visual field defects. 29

30 Lamotrigine ÚPartial and generalized seizures. ÚInhibits Na+ and Ca++ channels, also decreases release of glutamate. ÚCompletely absorbed. ÚGlucoronidated, so will not induce or inhibit enzymes. ÚSide Effects: Similar to carbamazepine. Skin rashes Cerebellovestibular symptoms. 30

31 ÚPartial Seizures Gabapentin and Pregabalin ÚGABA analogs, but work indirectly to increase GABA levels in the brain. ÚGood PK Properties. ÚEffective when combined with others. ÚSafe: somnolence, dizziness, ataxia. 31

32 Benzodiazepines ÚGABA mechanism, and, ÚNa+ channel inhibition in doses used in status epilepticus. 32

33 Benzodiazepines ÚDiazepam Status epilepticus ÚLorazepam Longer acting ÚClonazepam Petit mal, but causes sedation and drooling ÚNitrazepam Infantile Spasms 33

34 Valproic Acid (1969) ÚPetit mal and myoclonic epilepsy ÚMixed seizures. ÚBipolar disorder and migraine prophylaxis. 34

35 Valproic Acid ÚIncreases GABA levels by enhancing synthesis and inhibiting transaminase. ÚAlso, blocks NMDA receptors, Na+ channels and T-Ca++ channels. Ú90% bound to plasma proteins. 35

36 Valproic Acid Toxicity: ÚHepatotoxic ÚNeural tube defects Ú Thrombocytopenia. ÚAlopecia ÚGI. ÚInhibits metabolism of many drugs. 36

37 Ethosuximide (1960s) ÚPetit mal, still first choice. ÚBlocks transient Ca++ Currents ÚSafe. 37

38 Acetazolamide ÚHelpful in all types of seizures. ÚUsed as an adjunct to others in refractory seizures. ÚWorks by decreasing intracellular ph. ÚTolerance develops. ÚSpecial role for seizures at the time of menses. 38

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