It has been argued that for the use of multiple AEDs
to be rational, the combination of two drugs must
provide supra-additive therapeutic efficacy, whereby
the combined efficacy of the two drugs is greater
than when the drugs are given alone. Alternatively,
combining AEDs may be more advantageous than
prescribing monotherapy at standard doses if they
demonstrate simple additive efficacy but less than
additive side effects. However, pharmacokinetic
drug interactions often contraindicate specific drug
combinations.