monitor with anticonvulsants

^[1]

Monitor

therapeutic drug levels (also see Notes:)
- loading or dosage changes
- suspected toxicity
- large variations in levels (phenytoin)
- starting or stopping interacting drug
- diseases or physiologic changes
  - pregnancy
  - renal failure
- poor seizure control
- suspected non-compliance
- changes in method of administration
  - with or without food (valproate)
  - switching dosage form (phenytoin, valproate)
- potential malabsorption (phenytoin, valproate)
liver function tests
- carbamazepine, ethosuximide, felbamate, valproate (required)
- baseline & periodically (frequently for valprotate, especially during 1st 6 months of treatment)
- most anticonvulsants require dosage adjustments or cautious dosing for hepatic impairment

therapeutic levels not well established for many agents, valproate, lamotrigine
unclear benetic of routine therapeutic drug monitoring without clinical indication
trough levels in general preferred
free valproate & free phenytoin better than total levels in patients with renal or hepatic disease, the elderly, & in patients with hyperlipidemia