7 - Anticonvulsant medications Flashcards
What is a seizure?
When nerves in the brain fire spontaneously, causing (most often) muscle spasms and loss of consciousness
What are the 2 types of partial seizures?
- Simple (conscious)
- Complex (lost or altered consciousness)
Difference between partial and generalized seizures
- Partial = focal, one half of the brain
- Generalized = both halves of the brain (bilateral); complete loss of consciousness
Causes of seizures
- Idiopathic (epilepsy)
- Brain damage
- Diseases (infectious and autoimmune)
- Low glucose/calcium/ magnesium/sodium
- EtOH withdrawal
Types of generalized seizures
- 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
Characteristics of seizure disorders
- Last only 1-2 minutes
- Most are not life-threatening
What is the post-ictal period?
Time after the seizure until pt returns to normal baseline mental function
Definition of status epilepticus
- Repeated seizures w/o regaining consciousness in between
- Seizure episodes lasting 5 mins or longer
What is refractory status?
Exposing pt to 2 anticonvulsants (BZD and phenytoin) and pt is still seizing
How can anti-convulsant drugs be given?
- Prophylactically to prevent seizures after brain damage (ex: subarachnoid hemorrhage, traumatic brain injury, intracranial hemorrhage)
- Actively for a recent seizure
What is the most severe, life-threatening form of seizure activity?
Status epilepticus
Define non-convulsive status epilepticus
Condition in which electrographic seizure activity is prolonged and results in non-convulsive clinical sx (simply appears unconscious)
Common etiologies of status epilepticus
- Anticonvulsant withdrawal (best response to tx)
- Alcohol-related
- Drug toxicity
- CNS infection
1st line for status epilepticus
- Phenytoin +/- diazepam/lorazepam
- Some require addition of phenobarbital
Which drugs aren’t recommended in alcohol withdrawal seizures?
Phenytoin or phenobarbital
Which px are the worst responders to tx?
- Anoxic injury
- Drug toxicity
- CNS infection
- Metabolic abnormalities
What is included in the workup of seizure disorders?
- 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
Indications of phenobarbital
- Generalized tonic-clonic seizures
- Partial seizures
- Febrile seizures in children
Wagner equation
Clearance * Css = S * F * Ro (mg/h)
When should the wagner equation be used?
If half life / 4»_space;> dosing interval (only really use it for phenobarbital)
How often should you sample phenobarbital levels for a pt starting a new regimen in hospital?
Every day for the first few days b/c don’t care if its at steady state, care that its in therapeutic range
How do you calculate loading dose and maintenance dose for phenobarbital?
- Loading dose = desired concentration * Vd / S * F
- Maintenance dose (Ro) = Cl * desired concentration / S * F
What is special to note about carbamazepine?
- Metabolized to carbamazepine 10,11 epoxide (active)
- Substrate and inducer of CYP 3A4, so auto-induces itself
Can you load a pt w/ carbamazepine?
No, there may be more acute, but transient cerebellar sx
What can cause toxicity sx of carbamazepine?
- Accumulation of 10,11-epoxide metabolite
- Only measure serum levels so don’t know if accumulation occurs
