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IC4 ASM pharmacology Flashcards

1
Q

What are the three general types of seizures?

A
  • generalized (whole brain is affected)
  • partial (part of brain is affected)
  • status epilepticus (prolonged seizure)
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2
Q

What is the rationale behind antiepileptics?

A

seizures occur due to excessive synchronous depolarization of neurons –> therefore, antiepileptics serve to decrease membrane excitability by altering Na+ and Ca2+ conductance during action potential or to enhance inhibitory effect of GABA (inhibitory neurotransmitter)

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3
Q

What are the antiepileptics of focus for this IC?

A
  • phenytoin
  • carbamazepine
  • sodium valproate
  • benzodiazepine
  • barbiturates
  • levetiracetam
  • lamotrigine
  • topiramate
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4
Q

Of the list above, which are the first line for newly diagnosed partial and generalized tonic clonic seizures?

A

phenytoin
carbamazepine
sodium valproate

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5
Q

Describe the MOA of phenytoin

A

Blocks voltage-gated Na+ channel

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6
Q

When can phenytoin be used?

A

for all seizures except absence seizures

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7
Q

What quirks does phenytoin have?

A
  • narrow theraputic range
  • non-linear r/s between dose and plasma conc, requiring TDM (zero order kinetics)
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8
Q

Can phenytoin be used in pregnancy?

A

no; teratogenic

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9
Q

What are the common side effects of phenytoin?

A
  • CNS: dizziness, drowsiness
  • gingival hyperplasia
  • hirsutism
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10
Q

What are the rare and serious side effects of phenytoin?

A
  • hepatotoxicity (for all 1st gen ASMs)
  • hypersensitivity (SJS/TEN)
  • blood dyscrasias
  • IC6, 7: chronic S/Es - peripheral neuropathy, osteomalacia, suicidal ideation
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11
Q

Describe the MOA of carbamazepine

A

Blocks voltage-gated Na+ channel

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12
Q

When can carbamazepine be used?

A

for all seizures except absence seizures (same as phenytoin)

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13
Q

What are the common side effects of carbamazepine?

A
  • CNS (dizziness, drowsiness, ataxia)
  • GI (N/V, constipation)
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14
Q

What are the rare and serious side effects of carbamazepine?

A
  • hepatotoxicity (1st gen ASM)
  • blood dyscrasia (eg. anemia)
  • hypersensitivity (SJS, TEN)
    (same as phenytoin)
  • IC6, 7: hyponatremia, peripheral neuropathy, osteomalacia
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15
Q

Can carbamazepine be used in pregnancy?

A

no; teratogenic (major congenital malformation)
switch to levetiracetam/lamotrigine

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16
Q

Can carbamazepine be used in renal impairment?

A

yes; renal elimination is not the major route of elimination
! BUT - may cause renal toxicity (eg. interstitial nephritis, hyponatremia) - use w caution

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17
Q

Can carbamazepine be used in hepatic impairment?

A

yes - use w caution as major route of elimination; may cause hepatotoxicity

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18
Q

Can carbamazepine be used in elderly?

A

yes - use w caution if >65

(causes/exacerbates SIADH or hyponatremia + increased risk of psychiatric effects)

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19
Q

What quirks does carbamazepine have?

A
  1. undergoes autoinduction (induces CYP3A4) –> shortens half life with repeated doses, requiring dose increments over time
  2. PGx: risk of SJS/TEN for patients with HLA-B.1502 and HLA-A.3101
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20
Q

When is carbamazepine contraindicated?

A
  • concomitant use of MAOis
  • bone marrow depression
  • HLA-B.1502 or HLA-A.3101 positive
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21
Q

What is an important DDI to look out for carbamazepine?

A

clarithromycin (macrolide abx)

carbamazepine - 3A4 inducer + substrate –> ↓ conc of clarithromycin

clarithromycin - 3A4 inhibitor + substrate –> ↑ conc of carbamazepine

management: avoid clarithromycin and use other abx

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22
Q

Describe the MOA of sodium valproate

A
  1. Blocks voltage-gated Na+ and Ca2+ channels
  2. Inhibits GABA transaminase (enzyme that breaks down GABA inhibitory neurotransmitter)
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23
Q

When can sodium valproate be used?

A

all seizures, including absence seizures

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24
Q

What are the common side effects of valproate?

A
  • CNS: dizziness, drowsiness
  • GI: N/V, stomach upset, stomach cramp, diarrhoea
  • increase in appetite, weight gain (unique to valproate)
  • temporary hair loss
  • trembling of fingers & hands
  • irregular and/or painful menstruation
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25
What are the serious side effects of valproate?
* hypersensitivity, SJS/TEN * hepatotoxicity (1st gen ASM) * pancreatitis (unique to valproate) * blood dyscrasias (thrombocytopenia) * severe weakness/dizziness * suicidal ideation * blurred vision or double vision/unsteady movement
26
What 'PK quirk' does sodium valproate have?
high plasma protein binding; even displaces other antiepileptics saturable protein binding at therapeutic range; higher conc = higher free unbound conc = more likely to experience S/Es or toxicity
27
Can valproate be used in pregnancy?
no unless alternatives failed/unacceptable
28
Can valproate be used in breastfeeding?
yes; compatible but weight risk vs benefits
29
Can valproate be used in renal impairment?
yes - 1st gen ASMs mainly hepatically cleared
30
Can valproate be used in hepatic impairment?
no; not recommended in mild-moderate, contraindicated in severe (hepatotoxicity is a S/E) (vs carbamazepine - while 1st gen = mainly hepatic, it can be used w caution in hepatic impairment)
31
What side effects of antiepileptics are dose related?
* CNS: drowsiness, confusion, slurred speech, nystagmus (eye movement), ataxia (lack of coordination) * nausea * unusual behaviour * mental changes * coma
32
What side effects of antiepileptics are non dose related?
* hirsutism * acne * gingival hyperplasia (gum overgrowth) * folate deficiency * osteomalacia (bones become soft) * hypersensitivity (SJS)
33
Describe the MOA of benzodiazepines
binds to regulatory site on ligand-gated Cl- channel --> potentiates GABA-induced Cl- influx --> hyperpolarization --> membrane potential further away from threshold potential --> inhibition of generation of AP TLDR: enhances effects of inhibitory GABA neurotransmitter
34
What are some common benzodiazepines?
'-lam' --> midazolam, triazolam, alprazolam '-pam' --> clonazepam, lorazepam, diazepam
35
What are the benzodiazepines that can be used for status epilepticus?
* midazolam * lorazepam * diazepam
36
What are the side effects of benzodiazepines?
all due to CNS depression; * drowsiness * confusion * amnesia * impaired muscle coordination (don't drive or operate heavy machinery)
37
What happens during acute toxicity/overdose of benzodiazepines?
severe respiratory depression
38
What substance increases the risk of respiratory depression when used with benzodiazepines?
alcohol
39
What is the treatment for benzodiazepine overdose?
flumazenil (benzodiazepine antagonist)
40
Why are benzodiazepines not commonly used anymore?
risk of tolerance and dependence
41
Describe the MOA of barbiturates
same as benzos, but binds at a diff site; binds to regulatory site on ligand-gated Cl- channel --> potentiates GABA(A)-induced Cl- influx --> hyperpolarization --> membrane potential further away from threshold potential --> inhibition of generation of AP
42
State an example of a barbiturate
phenobarbital
43
When is phenobarbital used?
in pediatric/neonatal patients (IV loading dose --> IV/PO maintenance dose)
44
Why is barbiturates no longer commonly used?
dose-dependent depression on CNS
45
Can flumazenil be used for the treatment for barbiturate overdose?
nO~
46
Describe the MOA of levetiracetam
unclear; thought to be due to binding to SV2a protein found on surface of synaptic vesicles, preventing release of neurotransmitter
47
When can levetiracetam be used?
* monotherapy: partial onset seizures in newly diagnosed epilepsy * adjunctive therapy: partial seizures, generalized seizure (myoclonic, tonic-clonic)
48
Describe the PK profile of levetiracetam
linear with low inter and intra-subject variability (opp of phenytoin)
49
What are the common side effects of levetiracetam?
* headache * vertigo * cough * depression * insomnia
50
What are the rare and severe side effects of levetiracetam?
* agranulocytosis * suicidal thoughts * delirium, dyskinesia IC6, 7: behavioural disturbances
51
Describe the MOA of lamotrigine
blocks voltage-gated Na+ channel
52
When can lamotrigine be used?
* monotherapy: typical absence seizures * adjunctive/monotherapy: partial seizures, generalized (incl tonic-clonic) * initial/adjunctive: Lennox-Gastaut syndrome (severe childhood epilepsy)
53
Quick recap: what are the medications that can be used for absence seizures?
* sodium valproate * lamotrigine
54
What drugs decrease the half-life of lamotrigine when coadministered tgt?
* carbamazepine * phenytoin both are known potent inducers (though based on google search lamotrigine is not predominantly cleared by P450 system, just use this fact to memo bah)
55
What drugs increase the half-life of lamotrigine when coadministered tgt?
sodium valproate
56
What are the common side effects of lamotrigine?
* headache * aggression * tiredness
57
What are the rare and severe side effects of lamotrigine?
* hypersensitivity (SJS/TEN) * hepatic failure * agranulocytosis (same as levetiracetam) * hallucination * movement disorder (worsens PD)
58
Describe the MOA of topiramate
unclear; thought to be same as benzos & barbiturates (activate GABA-A to potentialte GABA-induced chloride influx)
59
When can topiramate be used?
* monotherapy: partial seizures, generalized (tonic-clonic) * adjunctive: Lennox-Gastaut syndrome (severe childhood epilepsy) * prophylaxis of migraine headaches in adults (not for acute treatment)
60
What are the common side effects of topiramate?
* depression * fatigue * nausea * weight loss
61
What are the rare and severe side effects of topiramate?
* neutropenia (VS agranulocytosis for levetiracetam & lamotrigine) * mania * tremor * transient blindness * hypersensitivity (SJS/TEN; same as lamotrigine) * hepatic failure (same as lamotrigine) * IC6, 7: speech fluency
62
When do we test for antiepileptic drug levels?
* assess compliance * assess toxicity * titrate phenytoin dose (most impt) IC7: indications for TDM - determine individual therapeutic range, assess lack of efficacy + toxicity + loss of efficacy

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