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Neurology 2 > Pharm - Seizures > Flashcards

Pharm - Seizures Flashcards

1
Q

Goals of therapy for seizure management

A
  • complete elimination of seizures
  • limit side effects
  • optimal quality of life
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2
Q

what is the drug interaction b/w anticonvulsant agents and combo oral contraceptives?

A

anticonvulsants that induce hepatic enzymes decrease the efficacy of combo oral contraceptive pills

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3
Q

need for folic acid in women planning pregnancy while taking antiseizure meds

A

0.4 mg per day

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4
Q

what is the general titration strategy when initiating antiseziure med?

A
  • start w/ monotherapy
  • gradually increase the dosage to that which is maximally tolerated and/or produces seizure freedom
  • start low, go slow
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5
Q

what is the general monitoring strategy when initiating antiseizure med?

A
  • monitor tx regularly

- regular f/u visits to ck drug concentration, blood counts and hepatic/renal function

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6
Q

what is required when switching from Depakote to Depakote ER?

A

the dose should be increased by 14-20%

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7
Q

significant pharmacokinetics of valproic acid (depakote)

A
  • extensively bound to albumin w/ saturable binding
  • inhibits hepatic metabolism (P450 system)
  • primarily metabolized in liver
  • crosses placenta w/ higher fetal levels than mother
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8
Q

what is the significant of valproic acid being extensively and saturablely bound to albumin?

A
  • the free fraction of valproic acid increases as serum concentration increases
  • need to monitor unbound serum concentrations
  • pts w/ low albumin will have more free drug in system
  • important if on other meds that are competitive binders of albumin
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9
Q

therapuetic serum concentration of valproic acid

A

50-100 mg/L

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10
Q

valproic acid and pregnancy

A

AVOID

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11
Q

what are the most common ADRs for valproic acid?

A
  • GI: n/v
  • tremor
  • thrombocytopenia
  • weight gain
  • hair loss
  • liver toxicity
  • PCOS
  • hyperammonemia
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12
Q

tremor ADR from valproic acid

A
  • one of the MC neurologic sx
  • w/i the first year of tx
  • looks like essential tremor
  • reversible if dc drug
  • reduce dose if possible or tx w/ propranolol
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13
Q

thrombocytopenia ADR from valproic acid

A
  • usually mild reduction (100k - 150k)
  • RFs: elderly, females, pts take >1g daily
  • pt may present w/ petecchiae
  • d/t bone marrow suppression or hypersensitivity reaction
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14
Q

weight gain ADR from valproic acid

A
  • can be significant
  • associated w/ increase in insulin levels
  • in first 3 mos of tx
  • women at higher risk
  • common
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15
Q

hair loss ADR fro valproic acid

A
  • associated w/ long term therapy
  • dose related
  • not complete loss, more alopecia
  • reduce dose if possible
  • recommend: biotin supplement, avoid taking valproic during meals, zinc/selenium supplement
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16
Q

liver toxicity ADR from valproic acid

A
  • the most serious ADR
  • can be fatal
  • happens mostly in kids <2 on valproic acid and another anticonvuslant
  • RFs: age <2, mental retardation, inborn errors of metabolism, several meds, difficult to control seizures
  • early in tx
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17
Q

pharmacokinetic properties of topiramate (Topamax)

A
  • 50% is excreted unchanged renally
  • titrate slowly every 1-2 weeks
  • linear kinetics
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18
Q

ADRs of topiramate

A
  • CNS:
  • word finding difficulty
  • memory impairment
  • thinking difficulties
  • nephrolithiasis
  • *anorexia/weight loss is a big one
  • diarrhea
  • paresthesias, fatigue, taste perversions
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19
Q

pharacokinetics of levetiracetam (Keppra)

A
  • 2/3 is renally eliminated unchanged
  • the rest is elimination of active metabolites
  • metabolism is independent of the CYP system (limits potential for interaction w/ other antiseizure drugs)
  • NOT an inducer of CYP system
  • higher clearance in kids
  • reduce dose in liver and renal insufficiency
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20
Q

ADRs of levetiracetam

A
  • CNS side effects are most common
  • agitation
  • irritability or lethargy
  • initiate dosing at 1/2 recommended dose
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21
Q

What are the advantages of levetiracetam

A
  • linear kinetics
  • not metabolized by P450 system
  • no significant drug interactions
  • well tolerated
  • transient sedation is the most troublesome ADR
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22
Q

what are the disadvantages of levetiracetam?

A
  • dosage adjustment needed in decreased renal function

- slower dose escalation to avoid CNS ADRs

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23
Q

what is important to remember about gabapentin (Neurontin)?

A

dose adjustments are required in patients w/ impaired renal function

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24
Q

ADRs of gabapentin

A
  • main one: sedation
  • use in caution w/ other meds
  • dizziness
  • ataxia
  • weight gain
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25
Q

pharmacokinetics of perampanel (fycompa)

A
  • extensively metabolized by liver
  • primarily by CYP3A4
  • prolonged and variable half-life (105 hrs)
26
Q

black box warning associated w/ perampanel

A

-serious neuropsychiatric effects including alteration of mood and aggression

27
Q

pharmacokinetics of carbamazepine (Tegretol) aka CBZ

A
  • metabolized in liber by CYP3A4
  • induces many enzymes causing rapid metabolism of other drugs
  • an active metabolite - influenced by other drugs
  • **induces its own metabolism (autoinduction )
28
Q

autoinduction of CBZ

A

important!

  • serum concentration rises over first 3-5 days
  • followed by gradual decline over next month d/t autoinduction
  • half life of the drug declines w/ chronic therapy
29
Q

what is the outcome caused by CBZ autoinduction?

A

-pts may achieve adequate response at first but control declines

30
Q

what is the therapuetic range of CBZ?

A

4-12 mcg/mL

31
Q

how does autoinduction of CBZ effect the dosing strategy?

A
  • usual starting dose: 2-3 mg/kg/day PO BID
  • increase dose by 200 mg every 2-3 weeks to allow for autoinduction to take place
  • do so until serum concentrations stabilize
  • continue to monitor every 2-3 weeks after each dosage change

**very important to monitor serum concentrations and for pt to be consistent in taking the drug!

32
Q

notable ADRs of CBZ

A
  • hyponatremia
  • leukopenia
  • idiosyncratic (agranulocytosis, aplastic anemia, morbilliform rash, stevens-johnson syndrome)
33
Q

hyponatremia d/t CBZ

A
  • = serum Na < 134 mEq/dL
  • incidence increases w/ age
  • dose related
  • increased responsiveness of collecting tubules to ADH
34
Q

leukopenia d/t CBZ

A
  • usually mild and reversible
  • redistribution of WBC is the cause
  • not a reason to stop drug unless WBC count drops <2,500 and absolute neutrophil count drops <1000
35
Q

screening needed when starting CBZ

A
  • HLA-B*1502 (main one)
  • HLA-B*3101
  • HLA-A*2402

*for risk of stevens-johnson syndrome

36
Q

HLA-B*1502 screening

A
  • screen pts w/ Asian ancestry d/t risk of stevens-johnsons syndrome
  • if results are positive: AVOID drug
37
Q

HLA-B*3101

A
  • increased risk of stevens-johnsons across all ethnic groups
  • some say test all CBZ-naive pts for this
38
Q

HLA-A*2402

A

-independent RF for stevens-johnsons in southern Chinese HAN population

39
Q

what is a major disadvantage of CBZ?

A

very teratogenic in the first trimester - higher incidence of spina bifida

40
Q

what are the 2 drugs structurally similar to CBZ?

A
  • eslicarbazepine (Aptiom)

- oxcarbazepine (Trileptal)

41
Q

eslicarbazepine (Aptiom)

A
  • NO autoinduction
  • there is a risk of stevens-johnsons d/t structural similarity to CBZ
  • also can cause hyponatremia
42
Q

oxcarbazepine (Trileptal)

A
  • NO autoinduction
  • there is a risk of stevens-johnsons d/t structural similarity to CBZ
  • also can cause hyponatremia
43
Q

what is important to remember about michalis-menton (aka non-linear) kinetics?

A

a small change in dose can result in a disproportionally large increase in serum concentrations w/ potential to cause toxicity

44
Q

therapuetic range of phenytoin (dilantin)

A

10-20 mg/L

45
Q

what are the 4 oral dosage forms phenytoin?

A
  • prompt release capsules (sodium salt)
  • extended release capsules (2 strengths; sodium salt)
  • suspension
  • chewable tablets
46
Q

considerations on changing dosage forms of phenytoin

A

**100 mg of phenytoin acid is equal to 92 mg phenytoin sodium

47
Q

what is the impact of food and enteral tube feedings on phenytoin availability

A

bioavailability of phenytoin can be decreased in pts on continuous enteral tube feeding

48
Q

phenytoin ADRs

A
  • gingival hyperplasia
  • vit. D deficiency
  • osteomalacia
  • hypothyroidism
  • megaloblastic anemia
  • hepatotoxicity

more rare but serious:

  • rashes
  • stevens-johnsons
  • pseudolymphoma
  • bone marrow suppression
  • lupus-like syndrome
  • hepatitis
49
Q

pharmacokinetics of lamotrigine (lamictal)

A
  • completely and rapidly absorbed (bioavailability 98%) not affected by food
  • clearance is higher in children and lower in elderly
  • doesn’t inhibit liver enzymes
  • low potential for kinetic interactions w/ other drugs
  • interacts w/ carbamazepine leading to increase in CNS ADRs
50
Q

what is the nature of the drug-drug interaction of b/w lamotrigine and valproic acid?

A

valproic acid substantially inhibits the metabolism of lamotrigine

*max inhibition occurring at valproic acid doses and serum concentrations of 500 mh/day and 40-50mcg/ml

51
Q

ADRs of lamotrigine in combo w/ other antiseizure meds

A
  • diplopia (w/ CBZ)
  • tremor (w/ valproic acid)
  • rash
52
Q

RFs for a serious rash w/ lamotrigine

A
  • concomitant use of valprioc acid
  • high initial doses or rapid doses used
  • children have higher incidence
  • more likely in those who had a rash d/t other tx
53
Q

advantages associated w/ lamotrigine

A
  • broad spectrum
  • multiple dosage forms
  • flexible
  • linear pharmacokinetics
  • not highly protein bound
  • doesn’t inhibit metabolism of other drugs
54
Q

CNS ADRs of phenobarbital

A 
CNS depression: 
-confusion 
-dizziness
-sedation
-HA
-hangover effect
-impaired judgement 
-confusion 
-respiratory distress 
CNS agitation: 
-anxiety
-hallucination 
-insomnia
-nervousness
-nightmares
55
Q

what is the black box warning for vigabatrin (Sabril)

A

FDA boxed warning in the US regarding permanent vision loss

56
Q

Which drugs can be monitored w/ serum concentrations?

A

phenobarbitol and ethosuximide

57
Q

folic acid dose for prevention of neural tube defects in women taking anticonvulsants

A

4 mg/d beginning at least 1-3 before conception through first 3 mos of pregnancy

58
Q

benefits of withdrawing anticonvulsant therapy

A
  • offers pts a sense of being cured
  • removes risk of ADRs
  • drugs are expensive
59
Q

risks of withdrawing anticonvulsant therapy

A
  • possibility of seizures recurring

- risk for seizure control not being regained to the same degree

60
Q

ID the meds used for status epilepticus

A
  • Benzos: lorazepam, diazepam, midazolam
  • phenytoin
  • fosphenytoin
  • phenobarbitol

Neurology 2 (21 decks)

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