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Antiepileptisc
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Central nervous system
Dr . Shadab Khan
The brain
The spinal cord
Anatomical classification Cerebral hemispheres Diencephalon
Thalamus Hypothalamus
Brain stem Midbrain Pons Medulla
Cerebellum
Spinal cord
Cerebrum
hypothalamus
thalamus
mid-brain
pons varolii
medulla oblongata
cerebellum
spinal cord
cerebral cortex
cerebrum
Acknowledgement: Picture of model from Mentone Educational Centre C15
The functional areas of the cerebrum sensory areas interpret impulses
from receptors. motor areas control muscular
movements. association areas are involved with
intellectual and emotional processes.
Functional areas of the cerebral cortex
Motor area for speech
Primary auditory area
Auditory association area
Primary sensory area
Primary motor area
Speech
Primary visual areaVisual
association area
Acknowledgement: Picture of model from Mentone Educational Centre C15
functions of cerebrum
thinking reasoning learning memory intelligence sense of responsibility perception of the senses initiation and control of voluntary
muscle contraction
simplified…
Back of brain: perception Top of brain: movement Front of brain: thinking
Hypothalamus
hypothalamus
thalamus
mid-brain
pons varolii
medulla oblongata
cerebellum
spinal cord
cerebral cortex
cerebrum
Acknowledgement: Picture of model from Mentone Educational Centre C15
The hypothalamus regulates: heart rate body temperature movement of food through the alimentary
canal food and water intake patterns of waking and sleeping contraction of the urinary bladder sexual cycles sensory information from internal organs associated with fear and anger the release of hormones from the pituitary
gland
BASAL GANGLIA
Include:• Caudate nucleus• Globus pallidus• Putamen• Amygdaloid
ClaustrumPartly
• Substancia nigra• Subthalamic nucleus
Brain Stem
Midbrain Pons Medulla
oblongata
The medulla oblongata regulates: heartbeat through its
cardiovascular centre
breathing rhythm through its respiratory centre
the diameter of blood vessels through its vasomotor centre
Cerebellum Two major hemispheres: three lobes each
• Anterior• Posterior• Floculonodular
Vermis: midline lobe connecting hemispheresSeparated from brain stem by 4th ventricle
Functions of cerebellum
Smooths, coordinates & fine tunes bodily movements
Helps maintain body posture Helps maintain equilibrium Also some role in cognition
Damage: ataxia, incoordination, wide-based gait, overshooting, proprioception problems
Spinal cord
http://www.apparelyzed.com/spinalcord.html
Spinal nerves
Divided based on vertebral locations 8 cervical 12 thoracic 5 lumbar 5 sacral 1 coccygeal Cauda equina (“horse’s tail”): collection
of nerve roots at inferior end of vertebral canal
The action of the spinal cordSensory neurons pick up signals from
theskin and transfer that information toconnector neurons in the spinal cord
and/orbrain.This information is relayed on to the
motorneurons in the spinal cord to illicit aresponse.
Major fiber tracts in white matter of spinal cord
Damage: to motor areas – paralysis
sensory motor
Ascending pathways:
sensory information by multi-neuron chains from body up to more rostral regions of CNS Dorsal column Spinothalamic tracts Spinocerebellar tracts
Descending pathways: motor instructions from brain to more caudal
regions of the CNS Pyramidal (corticospinal) most important to
know All others (“extrapyramidal”)
Blood-Brain Barrier
Tight junctions between endothelial cells of brain capillaries, instead of the usual permeability
Highly selective transport mechanisms Allows nutrients, O2, CO2 Not a barrier against uncharged and
lipid soluble molecules; allows alcohol, nicotine, and some drugs including anesthetics
Drugs Acting on the Central nervous System
ANTIEPILEPTIC DRUGS
Dr Shadab Khan
What is Epilepsy?
Epilepsy is a collective term for a group of disorders characterised by paroxysmal cerebral dysrthmia, menifesting as brief episodes (seizures) of loss or disturbance of conciousness with or without characteristic body movements(convulsions)sensory or psychiatric phenomina
Convulsion – Involuntary spasmodic contractions of any or all voluntary muscles throughout the body, including skeletal and facial muscles.
Seizures – Brief episode of abnormal electrical activity in the nerve cells of the brain -- detected on EEG
Epilepsy – Chronic, recurrent pattern of seizures
• Generalized
• Partial
Classification
1.Generalised tonic clonic seizures (GTCS) Grand mal epilepsy• Major epilepsy1-2 min• Commonest• Aura –cry –unconciousness –tonic
spasm of all body muscles-tonic jerking
• Prolongrd sleep and depression of all CNS functions
Generalised seizures
2.Absence SeizuresMinor epilepsy, petit mal •½ minute•Children•Apparent freezing•EEG: 3 cycle per second spike and wave pattern
3. Atonic SeizuresAkinetic Epilepsy ,Drop Attack
•Sudden loss of postural tone •Unconciousness•Excessive inhibitory discharges
4.Myoclonic seizures
Shock like momentary contraction of muscles of a limb or the whole body
5. Infantile Spasms
Hypsarrhythmias
Partial seizures
1.Simple partial seizures
2.Complex Partial seizures
3. Simple Partial or complex partial seizures secondarily generalized
Classification:
1. Drugs used to abolish seizures(anticonvulsants)
2. Drugs to prevent seizures (prophylaxis)
Classification:
1. Drugs used to abolish seizures(anticonvulsants)
2. Drugs to prevent seizures (prophylaxis)
Chemical Classification1. Barbiturate: phenobaritone2. Deoxybarbiturate : Primidone3. Hydantoin: Phenytoin4. Iminostillbene : Carbama zepine5. Succinimide: Ethosuximide6. Aliphatic Carboxylic acid: Valproic acid7. Benzodiazepines: Clonazepam , Diazepam8. Phenyltriazine : Lamotrigine9. Cyclic GABA analogue: Gabapentine 10.Newer Drugs: vigabatrine ,Zonisamide
ION Theory – movement of K+, Na+, Ca+, Mg+:
Stabilizes neurons: from becoming hyperexcited prevents excessive impulses to adjacent neurons
1. Increase threshold of activity in the motor cortexMakes it more difficult to excite; reduces response
2. Depress the seizure discharge from its originSuppress transmission of impulses from one nerve to the next
3. Decrease the speed of nerve impulse conduction within a given neuron
Mechanism of Action
•Prevention or control of seizure activity•Long-term maintenance treatment of epilepsy•Acute treatment of convulsions and status epilepticus
Status epilepticus: common seizure disorder –
life-threatening emergency characterized by tonic-clonic convulsions that occur in succession. Loss of consciousness, hypotension, hypoxia, cardiac dysrhythmias – brain damage and death may quickly resultOnce controlled, long term therapy is begun to prevent future seizures
•Brain Surgery - Head injuries = prophylactic AED Therapy
Indications
First efficatious antiepileptic 1912 Mechanism: GABA receptor mediated synaptic
inhibition Raises seizure threshold as well as limits spread
and suppresses kindled seizures Long plasma t1/2 (80-120 hrs)
Drawback :
• Sedative action
• Behaviouralar abnormalities
• Diminution of intelligence
• Impairment of learning
• Hyperactivity in children
• Mental confusion in older people
Phenobarbitone
Uses:
Generalised tonic Clonic seizuresSimple partial Seizures Complex partial Seizures
Gardinal ,syr Luminal
Phenytoin (Diphenylhydantoin)Synthesised in 1908 as a barbiturate analogue
Mechanism of Action•The drug slows the recovery of voltage-dependent sodium channels(stabilising effect) on all neuronal membranes including the peripheral nerves as well as on all non-excitable & excitable membranes •It inhibits the spread of seizure discharges in the brain & shortens the duration of after discharge•It reduces the neuronal sodium concentration leading to a reduction in PDS•Decreases post tetanic potentiation which is responsible for the spread of seizure activity
Pharmacokinetics
•Slowly absorbed from the gut •Plasma peak level 3-12 hrs after ingestion•70-95% albumin bound•Metabolised mainly by parahydroxylation in the liver•About 94% of a single dose is excreted in urine in 48 hrs•The dose increments must be smaller with increasing dosage since plasma concentration rises dispropotionately to the dose increment
Adverse Effects
At therapeutic level:
a) Gum Hypertrophy:Commonestb) Hirsutism,Acne,coarsening of facial
hairc) Hypersensitivity reactionsd) Megaloblastic Anemiae) Osteomalaciaf) Hyperglycemiag) During pregnancy: fetal hydantoin
syndromeHypoplastic phalangesCleft palate Hare lipMicrocephaly
At High plasma levels
a)Cerebellar & vestibular menifestationsb)Drowsiness, behavioral alterations,mental
confiusion,hallucinations,disorientations and rigidity
c) Epigastric pain,nausea and vomitingd)IV injections – local vascular injury• Intimal damage ang thrombosis of vein• Edema and discoloration of the injected limb• Rate of injection should not exceed 50mg/min • Fall in BP and cardiac arrhythmias
Interactionsa. Phenobarbitone inhibits phenytoin metabolismb. Carbamazepine and phenytoin increase each
others metabolismc. Valproate decreases its metabolismd. Chloramphenicol,
isoniazid,cemitidine,dicumaroland warfarin inhibit phenytoin metabolism
e. It inhibits warfarin metabilismf. Inceases degradation of
steroids,digitixin,doxycycline,theophyllineg. Sucralfate decrease it absorption
Uses
a) Generalised tonic-clonic,simple and complex partial seizure 100 mg BD max 400mg /day 5-8 mg /kg/day for children b) Status epilepticusc) Trigeminal neuralgia
DILACTIN ,EPTON,EPSOLIN , SYR FENTOIN –ER
Fosphentoin:
• Water soluble prodrug of phenytoin• To overcome the difficulties in I.V administration of
phenytoin in status epilepticus• Few vascular complications• Can be injected at a faster rate• Can be injected with both saline and glucose
FOSOLIN 50mg /ml in 2ml, 10 ml injection
Carbamazepine1960 mechanism of action similar to that of phenytoinPharmacological actions
Specific for trigeminal neuralgiaEffective in differentiation pain in diabetic neuropathy,cancer and multiple sclerosis
Pharmarmacokinetic:
Oral absorption slowMetabolised by liver (98%)Potent hepatic microsomal enzyme inducer
Adverse Effects
1. Nausea, sedation,dizziness,vertigo,diplopia anorexia2. Coma, convulsions and cardiovascular collapse3. Hypersensitivity reactions4. Agranulocytosis and aplastic anemia5. Water retention and hyponatremia in elderly6. Minor fetal malformations
Interactions
a)Reduces efficacy of haloperidol,oral contraceptives,lamotrigine and topiramate
b)Metabolism of carbamazepines induced by phenobarbitone,phenytoin,valproate and vice versa.
c) Erythromycin, flouxetine,isoniazid inhibit metabolism of carbamazepines
Uses
1.Grand mal & petit mal seizures2.Trigeminal and related neuralgias 3.Manic depressive illness and acute mania
Dose : 200-400mgTDS 15-30mg /kg/day
TEGRATOL,MAZETOL
OXCARBAZEPINE
•Newer congener of carbamazepine• better tolerated
OXETOL, OXCARB,OXEP 150,300,600MG TABS
ETHOSUCCIMIDE most frequently used succinimide Mechanism of ActionThe drug reduces the low threshold calcium currents in the thalamic neurones which are responsible for the generation of the absence seizures
Pharmacological actionsEffective only in petit mal epilepsy , does not induce liver enzymes
Pharmacokinetics
•Completely absorbed from GIT •20% excreted unchanged in urine •Rest metabolised by liver
Adverse Reactions:Anorexia, Nausea, Vomiting, Drowsiness, dizziness, skin rashes etc
Uses
Drug of Choice in petit mal epilepsy Dose 20-30mg /kg/day
ZARONTIN 250mg/5ml syr
Valproic Acid : Sodium Valproate Mechanism of Action •It’s a broad spectrum antiepileptic which probably acts at multiple sites •Actions similar to that of ethosuccimide and phenytoin•Inhibits the T type Ca++ current and also delays the recovery of the inactivated Na++ channels •It also inhibits GABA transaminase thus increasing the GABA
Pharmacokinetics•Rapidly and completely absorbed from the GI •More than 90% is metabolised in liver
Adverse Reactions
•Nausea, vomiting•Increases apetite and causes weight gain•Dose related hair loss•Hypoalbunemia•Hepatotoxicity with death
Uses
•Petit mal •Combined grand mal and petit mal•Myoclonic epilepsy•Partial epilepsy•Mania and bipolar illnesses
DIPROEX, VALANCE 125,250,500mg tabs
Clonazepam Benzodiazepine with prominent anticonvulsant properties Potentiate GABA induced Cl- influx to produce sedation and anticonvulsant properties
Pharmacokinetics Good oral absorptionCompletely metabolised in liver t1/2 24 hrs
Uses
Absence seizuresAdjuvant in myoclonic and akinetic epilepsyInfantile spasm Dose: A0.5-5mg tdsChildren: 0.02-0.2mg/kg/day
LONAZEP, CLONAPAX,RIVOTRIL 0.5, 1.0,2.0mg tab
CLOBAZAM 1,5 benzodiazepine
Uses
Adjuvant to other antiepileptic drugs
FRISIUM, LOBAZAM, CLOZAM 5,10,20,mg capsules
Diazepam
Drug of choice for emergency control of convulsions
•Status epilepticus•Tetanus •Eclampsia•Convulsant drug poisoning
Dose0.2-0.5mg/kg injected i.v slowly Maximum 100mg/day
Febrile convulsions in children : rectal instillation
Lorazepam :alternative to diazepam
Gabapentine
Lipophyllic GABA derivative
Mechanism of action
Crosses to the brain and enhances GABA release
Dose : start with 300mg OD & increase to 300-600 mg tds as required
NEURONTIN , GABANTIN
Uses
•Reduces seizurepartial seizures with or without generalization
•First line drug for pain due to diabetic neuropathy and post herpetic neuralgia• frequency in refractory Prophylactic effect in migraine
Vigabatrin
Inhibitor of GABA transaminase
•Anticonvulsant activity due to increase in synaptic GABA concentration •Effective in many cases of refractory epilepsy•Adjuvant medication
Adverse effects
•Behavioral changes•Depression •Psychosis
Dose : 2-4g daily
Children : 40-100mg /kg/day
Conclusion
Choice of drug and dose according to type of seizures and need of individual patients
Initiate treatment early starting with low dose and gradually increasing it
Treatment should be as simple as possible
All drug withdrawal should be gradual except in case of toxicity
Thank you