Neuro: Clinical Flashcards
ACVIM 2015 recommendations on when to start AEDs
- Known cause: Structural disease is present or prior brain injury is known.
- Acute severe seizures: Status epilepticus (>5 minutes duration or >3 seizures within 24 hours)
- Chronic seizures: >2 seizures within 6 months
- Severe post-ictal period
ACVIM 2015 recommendations for AEDs that may be used as mono therapy (order of preference)
- Phenobarbital, Imepitoin, 2. KBr
- Zonisamide, levetiracetam
- Primidone
ACVIM 2015 recommendations for AEDs that may be used as add on therapy (order of preference)
- Phenobarbital, levetiracetam, KBr, Zonisamide
- Imepitoin
- Primidone
Phenobarbital: MoA
Enhance the effectiveness of the GABAa receptor.
May also inhibits release of other neurotransmitters such as Act, nEP and glutamate.
KBr MoA
Bromide competes with chloride transport thus resulting in membrane hyperpolarisation.
Primidone MoA
85% is metabolised to phenobarbital
No benefit to using this over phenobarbital.
Imepitoin MoA
Partial agonist of the BNZ receptor of GABAa receptor.
Levetiracetam MoA
Largely unknown but may bind to SV2A which is a presynaptic protein
Zonisamide
May reduce sodium and T-type calcium channel opening on the post-synapse of excitatory neurons
When might trough sampling of phenobarbital be useful?
When patients seizure close to the next scheduled dose of the drug.
When should phenobarbital monitoring be performed following a start/change in therapy?
2w (steady state concentration)
6w (steady state of clearance - d/t liver enzyme induction)
then q6m and 2w after dose changes
When should KBr monitoring be performed
- 6-12 weeks
- annual basis
- if >3 seizures occur before next evaluation
- signs of toxicity
- perform >2 hours post dosing
What consideration should be made regarding dosing of levetiracetam when using this alongside phenobarbital?
May need higher doses due to phenobarbitals metabolic effects.
Which enzyme metabolises Zonisamide?
CYP3A4
Which AED drugs are affected by phenobarbital administration?
Levetiracetam and zonisamide