Table 2 Common drug-drug interactions associated with the new AEDs4

AEDOral contraceptivesWarfarinOther agentsEnzyme inducer?Enzyme inhibitor?Clinical notes
This is not meant to be a comprehensive list but represents the most common interactions, based on consensus of panel. There are no data on the interactions of new AEDs with many of the non-AED drugs. Future research may identify pharmacokinetic or pharmacodynamic interactions between new AEDs that are metabolized and non-AED drugs, that could result in adverse events.
AED = antiepileptic drug; MHD = monohydroxy derivative (metabolite of oxcarbazepine).
Gabapentin(−)(−)Modest decrease in gabapentin bioavailability with Maalox-TC(−)(−)No known interactions with other AEDs
Lamotrigine(+) Decrease in lamotrigine serum concentrations by oral contraceptives(−)(+/−)(−)Modest induction of glucuronidation with slight decrease in valproic acid plasma levels (25%) noted; interactions with cytochrome p450 isozymes not seen
Levetiracetam(−)(−)(−)(−)No known interactions with other AEDs
Topiramate(+) Dose dependent (>200 mg/d) decrease in ethinyl estradiol serum concentrations(−)Modest increase in haloperidol serum concentrations; modest decrease in lithium serum concentrations; modest decrease in digoxin serum concentrations(+/−)(+)Modest, dose-dependent induction of CYP 3A4 may reduce effectiveness of oral contraceptives; inhibition of CYP 2C19 may result in increases in phenytoin plasma concentrations
Tiagabine(−)(−)No interaction seen with erythromycin(−)(−)Potential for protein binding displacement (clinical relevance unclear)
Oxcarbazepine(+) Decrease in ethinyl estradiol serum concentrations(−)Modest decrease in felodipine serum concentration; modest decrease in MHD concentrations following verapamil administration; no interaction seen with erythromycin(+/−)(+)Modest, dose-dependent induction of CYP 3A4; possible induction of glucuronidation, with reduced plasma concentrations of lamotrigine noted; inhibition of CYP 2C19 may result in increased phenytoin or phenobarbital plasma concentrations
Zonisamide(−)(−)(−)(−)Clearance may be increased by enzyme-inducing AEDs