Antiepileptics

Question 1

Phenytoin mechanism

Answer 1

blocks Na channel in inactive states, stabilising membrane potential

Question 2

Carbamazepine mechanism

Answer 2

Blocks Na channels and potentiates GABA
similar stricture to TCAs

Question 3

Sodium valproate mechanism

Answer 3

Blocks sodium channels and potentiates GABA

Question 4

Levetiracetam mechanism

Answer 4

Binds SV2A, inhibits glutamate

Question 5

Phenobarbital mechanism

Answer 5

Barbituate
increases chloride channel opening leading to inc GABA
inhibits glutamate and sodium channels

Question 6

Ethosuximide mechanism

Answer 6

antagonism of the postsynaptic T-type voltage-gated calcium channel

Question 7

Phenytoin A+D

Answer 7

F0,9
PB90
vD 0.75
displaced by valproate and sulfonamides
T1/2 22

Question 8

Carbamazepine A+D

Answer 8

A: PO only F1
D: 70% PB, vD 1, higher in OD
Peak 6-8h
T1/2 36 → lower after self inducing

Question 9

Sodium valproate A+D

Answer 9

A: PO F>0.8 IV
D: 90% PB, small VD
Peak 2h
T1/2 9-16

Question 10

Antiepileptic with highest vD

Answer 10

Carbamazepine, still only 1ish

Question 11

Levetiracetam A+D

Answer 11

A: PO good absorb
D: nil signif PB, VD 0.5
T1/2 6-8h

Question 12

Phenobarbital A+D

Answer 12

A: PO F1
D: VD 0,6, 50% PB T1/2 4h

Question 13

In common antiepileptics

Answer 13

Good oral availability
High PB (except keppra)
Low VD
Hepatic metabolism (except keppra)

Question 14

Phenytoin M+E

Answer 14

M: hepatic 1st → 0 (suddenly very high serum levels)
CYP450 (inducer)
E: renal active and inactive

Question 15

Carbamazepine M+E

Answer 15

M: hepatic p450 (inducer)
E: renal
autoinducer - suddenly very low serum levels

Question 16

Sodium valproate M+E

Answer 16

M: hepatic to inactive
E: renal
Inhibs clearance phenytoin + carbamazepine

Question 17

Levetiracetam M+E

Answer 17

M: ⅓ deaminated in blood, ⅔ unchanged
E: renal

Question 18

Phenobarbital M+E

Answer 18

M: hepatic slow
P450 inducer
E: renal 20-50% unchanged

Question 19

Phenytoin SE and tox

Answer 19

dec HR and BP on loading
purple glove syndrome
Hypothyroid
Dec vit D
Neuro: ataxia, slurred speech, nystagmus, cerebellar
gingival hyperplasia

Question 20

Carbamazepine SE and tox

Answer 20

Hepatotox, SJS
Nausea, diplopia, ataxia, dec Na, rash, inc QRS, anticholinergic, seizure

Question 21

Sodium valproate SE and tox

Answer 21

GI - NV, abdo pain
Weight gain, hair loss, thrombocytopenia
Fine tremor
narrow TI
ammonaemia with encephalopathy
Teratogenic

Question 22

Levetiracetam SE

Answer 22

Thrombocytopenia
SJS
Dizziness
Ataxia
Mood changs

Question 23

Phenobarbital SE + tox

Answer 23

sedation
CI in porphyria and cirrhosis
tx urinary alkalinisation + flumazenil

Question 24

Antiepileptics 50% PB

Answer 24

Phenobarbital
Levetiracitem