Antiepileptics Flashcards
Phenobarbital target
GABA-a modulator
Primidone target
GABA-a modulator as Phenobarbital
Phenytoin target
Na+ Channel blocker
Fosphenytoin target
Na+ Channel blocker as Phenytoin
Ethosuximide target
Ca2+ Channel blocker
Valproate target
GABA-AT and SSA-DH Inhibitor
Divalproex sodium target
GABA-AT and SSA-DH Inhibitor: as Valproate
Carbamazepine target
Na+ Channel blocker
Oxcarbazepine target
Unknown, but known to be due to the “mono-hydroxy metabolite” : Licarbazepine
Eslicarbazepine acetate target
Unknown, but known to be due to Eslicarbazepine metabolite : S - Licarbazepine
Gabapentin target
alpha2delta-Ca2+ Channel blocker
Gabapentin enacarbil target
alpha2delta-Ca2+ Channel blocker
Pregabalin target
alpha2delta-Ca2+ Channel blocker
Vigabatrin target
Irreversible GABA-AT inhibitor (synthesis)
Felbamate target
Unknown
Lamotrigine target
Unknown
Topiramate target
Unknown
Zonisamide target
Unknown
Tiagabine target
GAT-1 Transporter blocker
Lacosamide target
Unknown
Levetiracetam target
SV2A modulator (vesicle protein)
Brivaracetam target
SV2A modulator (vesicle protein) > Levetiracetam
Rufinamide target
Na+ Channel modulator
Ezogabine target
K+ Channel activator
Perampanel target
AMPA antagonist (glutamate)
Cannabadiol target
Unknown
AED: Strong Inducers
Of various P450’s and UGT’s:
Phenobarbital / Primidone
Phenytoin / Fosphenytoin
Carbamazepine
AED: Moderate Inducers
3A4: Oxcarbazepine Eslicarbazepine acetate (due to metabolite) 2C9: Vigabatrin
AED: Weak Inducers
3A4:
Topiramate
Rufinamide
AED: 2C19 Inhibitors
Oxcarbazepine Eslicarbazepine acetate (due to metabolite)
AED: 2C9 Inhibitor
Valproate
AED: 2E1 Inhibitor
Rufinamide (weak)
AED: Epoxide Hydrolase Inhibitor
Valproate
AED: UGT Inhibition
Valproate (specific types - not in general)
AED’s most associated with skin disorders:
Most strongly with... - Phenobarbital - Phenytoin - Carbamazepine Less so with... - Oxcarbazepine - Lamotrigine
Phenobarbital metabolism
Para-hydroxylation by 2C9 / 2C19
Primidone metabolism
Oxidation to Phenobarbital
or
Multiple steps to Phenylethylmalonamide (PEMA)
Phenytoin metabolism
Para-hydroxylation by 2C9 > 2C19
Arene Oxide Intermediate
May proceed to inactive metabolite.
May proceed to Glutathione / Mercapturic acid metabolites which cause toxicities.
Fosphenytoin metabolism
Dephosphorylation by various phosphatases
Ethosuximide metabolism
Ethyl-hydroxylation by 3A4 / 2E1
Valproic acid metabolism
Direct Glucuronidation - Inactive or beta-oxidation to form 2-ene product - Active or * Reactive minor metabolite - Toxicity
Carbamazepine metabolism
3A4 oxidation - Epoxide intermediate
- Alkylation of proteins
- Epoxide Hydrolase to catechol (inactive)
Multi-Step metabolism to Iminoquinone form
- Alkylation of proteins
Oxcarbazepine metabolism
Reduction to mono-hydroxy metabolite (active)
- “Licarbazepine”
Eslicarbazepine acetate metabolism
Ester Hydrolysis - Eslicarbazepine
- S form of Licarbazepine
Gabapentin metabolism
Not appreciably metabolized
Gabapentin enacarbil metabolism
Amide-like bond broken to release Gabapentin - Not appreciably metabolized
Pregabalin metabolism
Less than 2% metabolized
Vigabatrin metabolism
Not significantly metabolized
Felbamate metabolism
Practice pathway: Results in electrophilic “atropaldehyde” metabolite that is toxic.
Lamotrigine metabolism
Major route - Glucuronidation
Minor route - P450’s create Arene Oxide
- Some Glucuronidated, some not.
- Serious skin rashes
Topiramate metabolism
70% unchanged.
30% many pathways.
Zonisamide metabolism
3A4 reduction in five membered ring
or
N-Acetylation of the sulfonamide group
Tiagabine metabolism
3A4 to 5-oxo-metabolite
Lacosamide metabolism
40% unchanged.
O-demethylation by 2C19 (mainly)
- Minor effects from inducers
Levetiracetam metabolism
No P450
66% excreted unchanged
Most hydrolyzed to inactive acid product
Brivaracetam metabolism
40% unchanged 2C19 - Hydroxylation on propyl side chain (inactive) Amide hydrolysis (inactive)
Rufinamide metabolism
Extensively metabolized.
Major route - Amide hydrolysis (inactive)
Can then be Glucuronidated
Ezogabine metabolism
No P450
Glucuronidation
N-acetylation
Perampanel metabolism
3A4 hydroxylation