Table 3.

AED Pharmacokinetics in the Elderly

Drug	Protein binding	Elimination	Comments
Carbamazepine	75–85%	hepatic CYP 3A4/5	Protein binding decreased with age Levels increased by erythromycin, prophoxyphene and grapefruit juice Decreases levels of calcium channel blockers (dilitiazem, verapamil), Decreases effect of warfarin, Decreases tricyclic antidepressant levels
Felbamate	<10%	hepatic
Gabapentin	<10%	renal	Elimination correlates with creatinine clearance No drug interactions
Lamotrigine	55%	hepatic- glucuronide conjugation	Levels decreased by inducing agents- carbamazepine, phenytoin, some hormones and others yet to be determined. Levels increased by vaproate
Levetiracetam	< 10%	renal	Very water solun]ble, IV formulation available No drug interactions
Oxcarbazepine	40%	hepatic	Causes hyponatremia
Phenobarbital	50%	Hepatic renal	Induces metabolism of many drugs
Phenytoin	80–93%	hepatic CYP 2C9 CYP 2C19	Protein binding decreased with reduced serum albumin and renal failure. Decreases levels of calcium channel blockers (dilitiazem, verapamil), Complicated interaction with warfrin Decreases tricyclic antidepressant levels Interacts with diabetes and arthritis medications Decreases effectiveness of cancer chemotherapy
Topiramate	9–17%	hepatic and renal	Inhibits CYP 2C19 and increase serum Phenytoin and other drug levels Induces CYP-3A4 isoenzymes
Valproic acid	87–95%	hepatic multiple pathways	Protein binding decreased in elderly. Inhibits glucuronidation and may increse levels of lamotirigine and other drugs Decreases platelet function
Zonisamide	40%	Hepatic   CYP 3A4	Weight loss and nephrolithiasis are issues