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Anti-Epilepsy - Coggle Diagram
Anti-Epilepsy
Overview of Epilepsy
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Origin site of abnormal neuronal firing determines the symptoms
~ motor cortex = abnormal movements or generalized convulsion
~ parietal or occipital lobe = visual, auditory & olfactory hallucinations
Abnormal electrical activity may results in:
(1) loss of consciousness
(2) abnormal movements
(3) atypical behavior
(4) distorted perceptions
Epilepsy: a neurological condition characterized by recurrent seizures
Seizures: occur due to brief disturbances in the electrical functions of the brain
Triggers
Environmental factors - sleep deprivation, alcohol intake & stress
Physiologic factors - alteration in blood gases, pH, hormones, electrolytes & blood glucose
Etiology of Seizures
Structural/metabolic epilepsy - drug abuse, tumor, head injury, hypoglycemia, meningeal infection & rapid withdrawal of alcohol from an alcoholic can precipitate seizures
Unknown cause - most epilepsy cases are of unknown cause where it occurs when no specific anatomic cause found. Patients can be treated chronically with anti-epilepsy medications or vagal nerve stimulation (invasive)
Genetic epilepsy - results from inherited abnormality in CNS => genetic mutations have been identified in patients with epilepsy syndromes
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Management of Epilepsy
Drug selection depends on classification of seizures; **patients' age, comorbid medical conditions, lifestyle & personal preference, cost of drugs & drug interactions
Sometimes, > single medications are required to optimize seizure control
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Gabapentin
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Precise MOA for anti-epileptic action is not known. Possibly- via inhibition of α2δ-1 subunit on high voltage-activated Ca channel
Well tolerated by elderly population with partial seizurs due to relatively mild adverse effects (only few drug interactions)
Analog of GABA, but does not act at GABA receptors, neither enhance GABA actions nor is converted to GABA
Carbamazepine
Therapeutic Uses
Efefctive for focal, generalized tonic-clonic seizures, trigeminal neuralgia & bipolar disorder. Note; SHOULD NOT BE PRESCRIBED for patients with ABSENCE SEIZURES because it may cause increase in seizures
Side Effects
Hyponatremia in some patients, esp in elderly & may necessitate a change in anti-epilepsy medication
Mechanism of Action
Blocks voltage-gated Na channels => inhibits depolarization => prevent release of glutamate => inhibits generation of repetitive action potentials in epileptic focus & preventing their spread
Pharmacokinetics
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An inducer of CYP1A2, CYP2C8, CYP2C9 & CYP3A4 & UDP glucuronosyltransferase (UGT) enzymes, which increases clearance of other drugs
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Lamotrigine
Pharmacokinetics
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UGT inducers (eg: carbamazepine & phenytoin) increases lamotrigine clearance - lower [lamotrigine], reduce its half-life
UGT inhibitors (eg: divalproex & valproate) results in a significant decrease in lamotrigine clearance - higher [lamotrigine]. Therefore, dosage should be reduced when co-administered
Therapeutic Uses
Effective for various seizure types, including focal, generalized, absence seizures & Lennox-Gastaut syndrome
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Precaution
Slow titration (particularly when adding lamotrigine to a regimen includes valproate) due to risk of rash, which may progress to a serious, life-threatening reaction
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Benzodiazepines
Uses
Most BZDs are reserved for emergency or acute seizure treatment (eg: status epilepticus) due to tolerance that may developed with prolonged use of BZDs
Mechanism of Action
Binds to allosteric site on GABA inhibitory receptors => increases affinity of GABA to its receptor => increases frequency of Cl- channel openings causing hyperpolarization => reduces neuronal excitability (reduced firing rate)
Examples
Lorazepam, Clonazepam, Midazolam, Diazepam
Diazepam is available for rectal administration to avoid or interrupt "prolonged generalized tonic-clonic seizures" when oral administration is not possible
Phenytoin & Fosphenytoin
Fosphenytoin
A pro-drug, rapidly converted to phenytoin in blood within minutes; administered IM
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Phenytoin
It exhibits saturable enzyme metabolism resulting in non-linear pharmacokinetic properties (small increases in daily dose can produce large increases in plasma conc, resulting in drug-induced toxicity)
Adverse effect
Results in CNS depression causing nystagmus & ataxia esp in elderly (highly susceptible to this effect)
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SHOULD NEVER be given IM, as it causes tissue damage & necrosis = "purple glove syndrome"
A CYP & UGT system inducer => it induces clearance of drugs metabolized by CYP2C & CYP3A families & UGT enzyme system
Mechanism of Action
Effective for treatment of focal & generalized tonic-clonic seizures & in treatment of status epilepticus
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Topiramate
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Adverse Effects
Sleepiness, weight loss, paresthesias, renal stones, glaucoma, oligohidrosis (decreased sweating) & hyperthermia
Mechanism of Action
Blocks Na & Ca channel, enhances GABA, antagonizes glutamate
Status Epilepticus
These may be focal (partial) or primary generalized, convulsive or non-convulsive
It is life-threatening, requires emergency treatment (usually administration of fast-acting medication eg: BZD, followed by slower-acting medication such as phenytion)
2 or more seizures occur w/o recovery with full consciousness in between episodes OR 2 continuous seizure activity occur for >5 min