====== Antiseizure medications interactions ======
Expected changes in plasma concentrations when an AED is added to a pre-existing regimen,,,,,,,,,,,,,,,
AED added,PB,PHT,PRM,ETS,CBZ,VPA,OXC,LTG,GBP,TPM,TGB,LEV,ZNS,VGB,FBM
PB,-,PHT ↑↓,NCCP,ETS ↓↓,CBZ ↓↓,VPA ↓↓,H-OXC ↓,LTG ↓↓,↔,TPM ↓↓,TGB ↓↓,↔,ZNS ↓↓,↔,FBM ↓↓
PHT,PB ↑,-,PRM ↓ PB ↑,ETS ↓↓,CBZ ↓↓,VPA ↓↓,H-OXC ↓,LTG ↓↓,↔,TPM ↓↓,TGB ↓↓,↔,ZNS ↓↓,↔,FBM ↓↓
PRM,NCCP,PHT ↑↓,-,ETS ↓↓,CBZ ↓↓,VPA ↓↓,?,LTG ↓↓,↔,TPM ↓↓,TGB ↓↓,↔,ZNS ↓↓,↔,FBM ↓↓
ETS,↔,↔,NE,-,↔,VPA ↓,NE,NE,NE,NE,NE,NE,NE,NE,NE
CBZ,↔,PHT I↓,PRM ↓ PB ↑,ETS ↓↓,-,VPA ↓↓,H-OXC ↓,LTG ↓↓,↔,TPM ↓↓,TGB ↓↓,↔,ZNS ↓↓,NE,FBM ↓↓
VPA,PB ↑↑,PHT ↓*,PB ↑↑,ETS I↓,CBZ-E ↑,-,↔,LTG ↑↑,↔,TPM ↓,EE,↔,↔,NE,↔
OXC,PB ↑,PHT ↑,?,?,CBZ ↓,↔,-,LTG ↓,NE,?,?,NE,?,NE,?
LTG,↔,↔,NE,NE,↔,↔,NE,-,NE,NE,NE,↔,↔,NE,NE
GBP,↔,↔,NE,NE,↔,↔,NE,NE,-,NE,NE,↔,NE,NE,NE
TBP,↔,PHT ↑,↔,NE,↔,VPA ↓,?,?,NE,-,?,NE,?,NE,?
TGB,↔,↔,↔,NE,↔,↔,NE,NE,NE,NE,-,NE,NE,NE,NE
LEV,↔,↔,↔,NE,↔,↔,NE,↔,↔,NE,NE,-,NE,NE,NE
ZNS,↔,↔,NE,NE,CBA ↑↓,↔,?,↔,NE,NE,NE,NE,-,NE,?
VGB,PB ↓,PHT ↓,PRM ↓ PB ↓,NE,CBZ ↑,↔,NE,NE,NE,NE,NE,NE,NE,-,NE
FBM,PB ↑↑,PHT ↑↑,?,?,CBZ ↓ CBZ-E ↑,VPA ↑↑,↔,↔,NE,?,?,NE,?,↔,-
PB = Phenobarbital; PHT = phenytoin; PRM = Primidone; ETS = Ethosuximide; CBZ = Carbamazepine; VPA = Valproic acid; OXC = Oxcarbazepine; LTG = Lamotrigine
GBP = Gabapentin; TPM = Topiramate; TGB = Tiagabine; LEV = Levetiracetam; ZNS = Zonisamide; VGB = Vigabatrin; FBM = felbamate
H-OXO = 10-hydroxy-oxcarbazepine(active metabolite of OXC); CBZ-E = Cabamazepine 10,11 epoxide
NE = None Expected; * Free (pharmacologically active) concentration may increase; NCCP = not commonly coprescribed; ↔ = No change; ↓ = a minor (or inconsistent) decrease in plasma concentration;
↓↓ = a clinically significant decrease in plasma concentration; ↑ = a minor (or inconsistent) increase in plasma concentration; ↑↑ = a clinically significant increase in plasma concentration.
source:Patsalos PN, Perucca E (2003) Clinically important drug interactions in epilepsy: general features and interactions between antiepileptic drugs. Lancet Neurol 2 (6):347-56. DOI: 10.1016/s1474-4422(03)00409-5 PMID: 12849151