Neurology/Psychiatry Drugs: Anti-Epileptics

Question 1

List the 5 main anti-epileptic drugs.

Answer 1

Carbamazepine
Sodium valproate
Phenytoin
Lamotragine
Levetiracetam

Question 2

Briefly describe the mechanism of action of carbamazepine. (2)

What are the indications for carbamazepine? (3)

What would you tell the patient when prescribing carcamazepine? (2)

Answer 2

MECHANISM OF ACTION:

1. Blocks voltage gated Na+ channels on the pre-synaptic membrane
   a. This blocks Na+ influx into the pre-synaptic bulb
2. This blocks the AP

INDICATIONS:
Epilepsy
Trigeminal neuralgia
Neuropathic pain

PATIENT INFO:

• Avoid alcohol
• Avoid grapefruit juice

Question 3

List 8 common side effects of carbamazepine.

List 1 severe, but rare side effect.

Answer 3

COMMON SIDE EFFECTS:
Dizziness
Dry mouth
Ataxia
Fatigue
Headache
Diplopia
Blurred vision
Hyponatraemia

RARE SIDE EFFECTS:
Stevens-Johnson syndrome

Question 4

What are the important pharmacokinetics/dynamics for carbamazepine? (4)

Answer 4

IMPORTANT PHARMA INFO:
-Response is variable

• Drug interactions:
  1. CYP450 INDUCER
  2. GRAPEFRUIT
• Resistance is possible, via RALBP1 TRANSPORTER
• HLA-B*1502 gene increases risk of SJS; avoid in these patients

Question 5

Describe the mechanism of action of sodium valproate. (2)

What are the indications for sodium valproate? (3)

Answer 5

MECHANISM OF ACTION:
1. Weak Na+ channel blocker at the synapse

2. Inhibits GABA metabolism by inhibiting GABA degrading enzymes
   a. Therefore less GABA is degraded and levels increase
   b. Increased GABA levels prevents AP transduction

INDICATIONS:
Epilepsy
Bipolar disorder
Depression

Question 6

List 5 common side effects of sodium valproate.

List 2 less common side effects (<10%).

List 1 rare, but serious side effect of sodium valproate.

Answer 6

COMMON SIDE EFFECTS:
Nausea
Diarrhoea
Gastric irritation
Weight gain
Hyponatraemia

LESS COMMON SIDE EFFECTS:
Behavioural disturbances
Confusion

RARE SIDE EFFECTS:
Stevens-Johnson syndrome

Question 7

Briefly detail important pharmacokinetics/dynamics for sodium valproate.

What would you tell the patient when prescribing sodium valproate? (3)

Answer 7

IMPORTANT PHARMA INFO:

• Drug interactions:
  1. CYP450 inhibitor
  2. Other anti-epileptic drugs
• Absorption from GI tract depends on:
  a. Formulation
  b. Time administered

PATIENT INFO:

• Avoid alcohol
• Take with food (but NOT milk)
• Monitoring of LFTs necessary during first 6 months

Question 8

Briefly describe the mechanism of action of phenytoin. (1)

What are the indications for phenytoin? (2)

Answer 8

MECHANISM OF ACTION:

1. Voltage-gated Na+ channel blocker on pre-synaptic membrane
   a. This prevents Na+ influx and AP transmission

INDICATIONS:
Epilepsy (including status epilepticus)
Trigeminal neuralgia

Question 9

List 7 common side effects of phenytoin.

List 3 severe, but rare side effects of phenytoin.

Answer 9

COMMON SIDE EFFECTS:
Insomnia
Headache
Rash
Constipation
Vomiting
Gingival hyperplasia
Liver damage

RARE SIDE EFFECTS:
Stevens-Johnson syndrome
Leukopenia
Thrombocytopenia

Question 10

Discuss the important pharmacokinetics/dynamics of phenytoin. (3)

What would you tell the patient when prescribing phenytoin? (3)

Answer 10

IMPORTANT PHARMA INFO:

• Drug interactions:
  1. CYP450 inducer
  2. Other anti-epileptic drugs
• Narrow therapeutic index
• Non-linear relationship between dose and plasma concentration

PATIENT INFO:

• Avoid alcohol
• Take with food
• Do NOT take calcium, aluminium, magnesium OR iron supplements within 2 hours of phenytoin

Question 11

Describe the mechanism of action of lamotrigine. (2)

What are the indications for prescribing lamotrigine? (2)

Answer 11

MECHANISM OF ACTION:
1. Inhibits voltage gated Na+ channels in the pre-synaptic membrane

2. Inhibits voltage gated Ca2+ channels in the pre-synaptic membrane

INDICATIONS:
Epilepsy
Depressive episodes in bipolar disorder

Question 12

List 7 common side effects of lamotrigine.

List 2 rare, but serious side effects of lamotrigine.

Answer 12

COMMON SIDE EFFECTS:
Nausea
Vomiting
Diarrhoea
Tremor
Insomnia
Blurred vision
Aggression

RARE SIDE EFFECTS:
Stevens-Johnson syndrome
Toxic epidermal necroylsis

Question 13

Discuss important pharmacokinetics/dynamics of lamotrigine. (1)

What would you tell the patient when prescribing lamotrigine? (2)

Answer 13

IMPORTANT PHARMA INFO:
-Half-life doubled in chronic renal impairment; dose adjustment needed

PATIENT INFO:

• Seek medical advice if rash appears
• Can be taken without regard to meals

Question 14

Describe the mechanism of action of levetiracetam. (2)

List the indications for prescribing levetiracetam. (1)

Answer 14

MECHANISM OF ACTION:
1. SV2A is a synaptic vesicle protein needed for neurotransmitter release

2. Levetiracetam blocks SV2A, therefore blocks neurotransmitter release

INDICATIONS:
Epilepsy

Question 15

List 6 common side effects of levetiracetam.

Answer 15

Headache
Fatigue
Anxiety
Irritability
Drowsiness
Constipation

Question 16

Describe the important pharmacokinetics/dynamics of levetiracetam. (3)

What would you tell the patient when prescribing levetiracetam? (2)

Answer 16

IMPORTANT PHARMA INFO:

• GI tract absorption is rapid and almost complete (99%)
• Not affected by food
• Not metabolised by CYP450

PATIENT INFO:

• May affect ability to drive/operate machinery
• NOT recommended during pregnancy/breastfeeding