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Clinical Pharmacology > Antiepileptics > Flashcards

Antiepileptics Flashcards

1
Q

Idiopathic epilepsy Cause and breed predilection

A

Unknown cause- hereditary or genetic

Breed= Goldens, Labs, Germ shep, beagles etc

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2
Q

Idiopathic epilepsy onset of first seizure

A

1-5 years

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3
Q

IE- are there interictal neurologic deficits

A

No

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4
Q

IE- how is diagnosis made

A

Ruling out structural and metabolic causes

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5
Q

IE treatment

A

1= eliminate underlying cause

If can’t do that, want Symptomatic TX with anticonvulsants

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6
Q

When should I treat with anticonvulsants? (Name 3 things)

A

More than 1 seizure per month
Cluster seizures (lots in a short time period)
Status epilepticus

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7
Q

Therapeutic goals for seizures in vetmed

A

Acute- end seizure activity as rapidly and effectively as possible, w/o adverse effects

Maintenance- decrease FREQ and SEVERITY of seizures (RARELY ABOLISH in vetmed)

Manage Owner expectations!!

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8
Q

Acute vs chronic seizure management

A

Acute- HIGHLY lipid soluble, rapid CNS concentrations

Chronic - for maintenance

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9
Q

Pharmacological effect is ______ to drug concentration at site of action

A

Proportional

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10
Q

Drug concentration at site of action is ______ to the drug concentration in blood

A

Proportional

Measure drug concentration in blood!!

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11
Q

Therapeutic Drug Monitoring (TDM)— LOOK AT GRAPH

What is the importance of HL?

A

We recommend TDM after 5HL (takes 5HL for drug to reach SS levels). We want to know if our selected dose has achieved the DESIRED blood concentration at STEADY STATE (we want it in the THERAPEUTIC RANGE)

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12
Q

TDM: what is the importance of elimination half life? SEE GRAPH

Think of example with Phenobarbital

A

It determines DOSE INTERVAL

Ex. Phenobarbital elimination HL is 48 hours. But for some dogs, it can be less than 24 hours— need to SHORTEN the dosing interval (i.e. give q8 instead of q12) to KEEP IN THERAPEUTIC RANGE

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13
Q

Trough concentration (Cmin)- what is it, when does it occur

A

Plasma concentration of drug at LOWEST level during dosing interval

Occurs immediately PRIOR to the next dose

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14
Q

Peak concentration, what is it and when does it occur

A

Cmax or Cpeak

Maximum plasma concentration that occurs during the dosing interval

Occurs within a few hours after dosing

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15
Q

Relationship of efficacy vs toxicity and TROUGH/PEAK

A

Efficacy- Look at trough sample (are the drug concentrations staying within the therapeutic level?)

Toxicity- Look at peak sample (are the drug concentrations reaching toxic levels?)

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16
Q

TDM- loading dose (what is used for? When is it indicated? )

A

Used to get plasma drug concentrations into therapeutic range as fast as possible

Indications- in some patients, it would be detrimental to wait 5 drug HLs to reach SS

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17
Q

What is the risk of using loading dose?

A

Patient has not had time to adjust to pharmacological effects of the drug GRADUALLY —> risk of adverse effects= greater

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18
Q

Loading dose— dosing

A

One large dose or can be split into a few smaller doses over several days (Bromide)

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19
Q

Is TDM something that can only be done at speciality hospitals

A

No! Do not hesitate to take a blood sample and evaluate

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20
Q

What happens with abrupt withdrawal of anticonvulsants, and what can we do about that?

A

Precipitates status epilepticus

Make sure to educate client, wean attends off GRADUALLY

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21
Q

Name 3 maintenance anticonvulsants

A

PBL

Phenobarbital
Bromide
Levetiracetam

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22
Q

What does GABA do?

A

GABA stimulation —> opens Chloride channel —> hyperpolarization of neuronal cell

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23
Q

Glutamate

A

A stimulatory NT

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24
Q

Phenobarbital effects on GABA and glutamate

A

Enhances GABA (an inhibitory NT) effects —> CL channel open —> hyperpolarization of neuronal cell

Inhibits glutamate activity —> inhibits the stimulatory NT

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25
Q

Phenobarbital main MOA

A

Primarily stimulates GABA gated Chloride channel (GABA = inhibitor NT)

Basically, increases INHIBITION

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26
Q

Phenobarbital- metabolism

A

Metabolized by liver (C P450)

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27
Q

Phenobarbital PK Considerations (HL, SS, therapeutic concentrations) in dogs

A

HL average is 48 hours (range 12-125 hours)

5HL to SS

Therapeutic concentrations = 15-40 micrograms/mL

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28
Q

Phenobarbital in horses- HL

A

Shorter HL, so administer more frequently

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29
Q

Phenobarbital adverse effects that are CNS mediated (which wanes after a few weeks?)

A

CNS mediated: PU, PD, PP

Sedation and ataxia (often seen after starting therapy, but should decease after a few weeks)

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30
Q

Phenobarbital- Most common adverse drug reaction

A 
Hepatotoxicity 
DOSE related (>30 micrograms/mL= higher risk)
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31
Q

Phenobarbital and effect on ALP and ALT

A

PB induces ALP (similar to glucocorticoids) and 2-5x is normal
Adverse if 5-10x baseline?

ALT- mild to moderate increases common

32
Q

PB – make sure to monitor what with CBC CHEM

A

Liver enzymes and liver function! Bile acids, albumin, cholesterol

33
Q

PB other adverse drug affects (notes)

A

CNS mediated PUPDPP, sedation, ataxia
BM: neutropenia and pancytopenia (less common)
Metabolism of thyroid hormones

34
Q

PB and CYP450

A

induces CYP450 therefore is a “perpetrator” of drug interactions

but also metabolized BY CYP450 and is a “victim” of drug interactions as well

35
Q

Monitoring time frame for PB

A

2 weeks (since HL is about 2 days, and want 5 HL) after starting PB or after any dose change (at SS): check PB level

Every 6 months- check CBC CHEM, UA, Bile acids (pre and post), PB level

*check for neutropenia too besides liver things

36
Q

most common bromide

A

KBr

37
Q

Bromide- MOA

A

transverses chloride channels resulting in hyperpolarization (inhibition) of neurons

38
Q

Bromide metabolism

A

“not metabolized”

100% excreted by kidney = choice for liver disease

39
Q

KBr half life and SS

A

25 days in dogs

SS= 4 months

40
Q

For KBr, how does the HL influence dosing

A

HL is long (25 days) and since SS is 4 months, it is not often appropriate to wait 4 months to reach SS in a patient with seizures.
Use loading dose to achieve SS more quickly

41
Q

For KBr, does TDM sample collection timing matter

A

no, doesn’t matter if you take concentration after dosing or AT trough…HL is too long (25 days)

42
Q

KBr formulation options and preferred

A

Tablets, capsules, solution (preferred)

Tablets may damage gastric mucosa

43
Q

KBr and GI effects

A

“salt”- hypertonicity may cause direct GI irritation and vomiting
GIVE WITH FOOD!

44
Q

Bromide- adverse drug reactions

A 
CNS depression (ataxia, sedation)
PUPD, PP
GI signs, pancreatitis
Fatal resp distress in 30-50% in cats- AVOID use in cats
NOT LIVER
45
Q

Bromide CNS depression- when?

A

Occurs at higher doses, during initial dosing, and definitely AFTER LOADING

–> worse in beginning, then improves

46
Q

Why avoid Bromide in cats

A

30-50% have FATAL resp distress

47
Q

Does Bromide cause liver toxicity

A

No liver toxicity !

48
Q

Bromide drug/diet interactions

A

Furosemide enhances bromide excretion, same goes for saline & increase in dietary salt

49
Q

What can you see on clin path results due to bromide use

A

Br measured as Cl –> may see alarming Cl results, as high as 200mEq/L

50
Q

Levetiracetam (Keppra) MOA

A

Interferes with presynaptic NT release

51
Q

Levetiracetam - metabolism

A

NO HEPATIC METABOLISM

Primary RENAL elimination

52
Q

Levetiracetam HL

A

about 4 hours in dogs (TID due to short HL), 5-6 hours in cats (TID), 7-8 hours in horses (BID)

53
Q

Levetiracetam use by neurologists

A

Some use as 1st choice antiepileptic for dogs and cats, but clinical results are similar to other antiepileptics (not superior or inferior to bromide or PB)

Minimal side effects, safe for liver

54
Q

Levetiracetam also known as

A

Keppra

55
Q

Levetiracetam clinical results in cats

A

3 month trial- 7 out of 10 had positive response, tolerable side effects

Notes say that used less in cats, so monitor carefully

56
Q

Maintenance anticonvulsants

A 
Many others (human) drugs that are 3rd line for dogs
Zonisamide = next most commonly used (besides PB, Br, and Keppra)
57
Q

What are our initial choices for anticonvulsants

A

PB or KBr usually

Levetiracetam and Zonisamide are also reasonable choices

58
Q

What happens if seizures continue in frequency or increase in severity with PB

A

Increase dose of PB until reaching the mid 30s ug/mL -or- side effects unacceptable

59
Q

What happens if seizures continue in frequency or increase in severity with KBr

A

Increase dose of KBr until side effects are unacceptable

60
Q

Use of multiple anticonvulsants- when can you add a second drug

A

When you maxed out on first drug (we rarely take them off an anti seizure drug)
sometimes need a third or fourth anticonvulsant

61
Q

Aspen- case

Differentials for having cluster seizures while on PB

A

Subtherapeutic concentrations of PB
Refractory epilepsy
Progressive disease (not idiopathic epilepsy, i.e. parasitic )

62
Q

Plan for Aspen- cluster seizures on PB

A

Trough phenobarbital level
If 13 ug/mL- increase PB dose
If 35 ug/mL- add 2nd drug, reconsider diagnosis
Consider MRI

If really high- could consider DRUG interactions with PB (drugs that inhibit cyt P450)

63
Q

Acute seizure management– what route is preferred and drug

A

IV, Diazepam (valium)

64
Q

What drug to avoid for acute seizure management and why

A

ORAL- delayed absorption, possible aspiration, risk of injury

65
Q

What other routes for Diazepam

A

If IV difficult in seizing patient, or owners unable to administer it IV, consider:

IM/SQ (but erratic absorption, painful IM)
Rectal !!
Intransal

66
Q

Rectal Diazepam pros

A

Reaches peak concentrations in systemic circulation in minutes, can send home w/ owners

67
Q

Diazepam MOA

A

enhance GABA activity (inhibitor NT)

68
Q

Diazepam PK considerations (3)

A

High lipid solubility
Short HL
Metabolized by liver

69
Q

Diazepam – importance of high lipid solubility

A

Fast distribution to CNS (TX of choice for acute seizures!)

70
Q

Diazepam– what to keep in mind with its HL

A

Short HL requires frequent administration

Not good as maintenance drug

71
Q

Diazepam metabolism

A

Liver

72
Q

Diazepam adverse reactions

A

Sedation (all species

Idiosyncratic hepatic necrosis (cats only)– RARE BUT FATAL!!

73
Q

Idiosyncratic hepatic necrosis with what drug

A

Diazepam– cats

74
Q

Diazepam drug interactions

A

Not a problem clinically

75
Q

Diazepam practical considerations (think plastic etc)

A

Binds to plastic

Light sensitive

76
Q

Levetiractam for seizure management

A

See study..

Rectal admin

77
Q

Anesthetic agents for acute seizure management

A

3rd choice, for extremely refractory cases
I.e. Propofol and isoflurane
Note- propofol may cause seizures in cats

Clinical Pharmacology (7 decks)

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