Which antiseizure medication has a therapeutic range commonly cited as 10-20 mg/L?

Which antiseizure medication has a therapeutic range commonly cited as 10-20 mg/L?

• A. Phenytoin
• B. Valproate
• C. Carbamazepine
• D. Lamotrigine

Answer: (A)

Therapeutic drug monitoring rests on the idea that each antiseizuremedication has a concentration range in which it works best without causing toxicity. For phenytoin, that commonly cited window is about 10–20 mg/L. Staying within this range helps ensure seizures are controlled while minimizing adverse effects, and it’s particularly important because phenytoin’s metabolism becomes saturable at higher concentrations, so small increases in dose can lead to disproportionately large rises in levels and toxicity signs such as ataxia or nystagmus. Valproate is usually targeted higher, around 50–100 mg/L; carbamazepine sits in roughly 4–12 mg/L; and lamotrigine dosing is guided more by clinical response and tolerability rather than a single universal trough level. That combination of ranges makes phenytoin the option tied most closely to the 10–20 mg/L range.

Therapeutic drug monitoring rests on the idea that each antiseizuremedication has a concentration range in which it works best without causing toxicity. For phenytoin, that commonly cited window is about 10–20 mg/L. Staying within this range helps ensure seizures are controlled while minimizing adverse effects, and it’s particularly important because phenytoin’s metabolism becomes saturable at higher concentrations, so small increases in dose can lead to disproportionately large rises in levels and toxicity signs such as ataxia or nystagmus.

Valproate is usually targeted higher, around 50–100 mg/L; carbamazepine sits in roughly 4–12 mg/L; and lamotrigine dosing is guided more by clinical response and tolerability rather than a single universal trough level. That combination of ranges makes phenytoin the option tied most closely to the 10–20 mg/L range.