7 - Anticonvulsant medications

Question 1

What is a seizure?

Answer 1

When nerves in the brain fire spontaneously, causing (most often) muscle spasms and loss of consciousness

Question 2

What are the 2 types of partial seizures?

Answer 2

• Simple (conscious)

- Complex (lost or altered consciousness)

Question 3

Difference between partial and generalized seizures

Answer 3

• Partial = focal, one half of the brain

- Generalized = both halves of the brain (bilateral); complete loss of consciousness

Question 4

Causes of seizures

Answer 4

• Idiopathic (epilepsy)
• Brain damage
• Diseases (infectious and autoimmune)
• Low glucose/calcium/ magnesium/sodium
• EtOH withdrawal

Question 5

Types of generalized seizures

Answer 5

• Tonic-clonic (stiffening of limbs followed by jerking)
• Myoclonic (brief, rapid contractions) **very resistant to drug therapy
• Absence (lapses of awareness, staring)
• Atonic (abrupt loss of muscle tone, head drop, loss of posture) **very resistant to drug therapy

Question 6

Characteristics of seizure disorders

Answer 6

• Last only 1-2 minutes

- Most are not life-threatening

Question 7

What is the post-ictal period?

Answer 7

Time after the seizure until pt returns to normal baseline mental function

Question 8

Definition of status epilepticus

Answer 8

• Repeated seizures w/o regaining consciousness in between

- Seizure episodes lasting 5 mins or longer

Question 9

What is refractory status?

Answer 9

Exposing pt to 2 anticonvulsants (BZD and phenytoin) and pt is still seizing

Question 10

How can anti-convulsant drugs be given?

Answer 10

• Prophylactically to prevent seizures after brain damage (ex: subarachnoid hemorrhage, traumatic brain injury, intracranial hemorrhage)
• Actively for a recent seizure

Question 11

What is the most severe, life-threatening form of seizure activity?

Answer 11

Status epilepticus

Question 12

Define non-convulsive status epilepticus

Answer 12

Condition in which electrographic seizure activity is prolonged and results in non-convulsive clinical sx (simply appears unconscious)

Question 13

Common etiologies of status epilepticus

Answer 13

• Anticonvulsant withdrawal (best response to tx)
• Alcohol-related
• Drug toxicity
• CNS infection

Question 14

1st line for status epilepticus

Answer 14

• Phenytoin +/- diazepam/lorazepam

- Some require addition of phenobarbital

Question 15

Which drugs aren’t recommended in alcohol withdrawal seizures?

Answer 15

Phenytoin or phenobarbital

Question 16

Which px are the worst responders to tx?

Answer 16

• Anoxic injury
• Drug toxicity
• CNS infection
• Metabolic abnormalities

Question 17

What is included in the workup of seizure disorders?

Answer 17

• Characterize the seizure type
• Clinical investigations targeting the cause are conducted
• Most appropriate therapy is selected
• Often 1st single seizures don’t require long-term tx
• Treat only those w/ recurrent seizures, those w/ status epilepticus, or those w/ structural predisposition

Question 18

Indications of phenobarbital

Answer 18

• Generalized tonic-clonic seizures
• Partial seizures
• Febrile seizures in children

Question 19

Wagner equation

Answer 19

Clearance * Css = S * F * Ro (mg/h)

Question 20

When should the wagner equation be used?

Answer 20

If half life / 4&raquo_space;> dosing interval (only really use it for phenobarbital)

Question 21

How often should you sample phenobarbital levels for a pt starting a new regimen in hospital?

Answer 21

Every day for the first few days b/c don’t care if its at steady state, care that its in therapeutic range

Question 22

How do you calculate loading dose and maintenance dose for phenobarbital?

Answer 22

• Loading dose = desired concentration * Vd / S * F

- Maintenance dose (Ro) = Cl * desired concentration / S * F

Question 23

What is special to note about carbamazepine?

Answer 23

• Metabolized to carbamazepine 10,11 epoxide (active)

- Substrate and inducer of CYP 3A4, so auto-induces itself

Question 24

Can you load a pt w/ carbamazepine?

Answer 24

No, there may be more acute, but transient cerebellar sx

Question 25

What can cause toxicity sx of carbamazepine?

Answer 25

• Accumulation of 10,11-epoxide metabolite

- Only measure serum levels so don’t know if accumulation occurs