Pharmacokinetic measurement of mephenytoin (or related metabolite) via mass concentration in plasma

What This Test Measures

This test quantifies the concentration of mephenytoin (or its active metabolite) in your plasma. Mephenytoin is a medication used primarily in the past for treating epilepsy, though newer antiepileptic drugs are more commonly prescribed today. The measurement helps assess drug levels in your bloodstream to ensure therapeutic effectiveness without excessive exposure.

Why It’s Ordered

Your healthcare provider may order this test if you’re taking mephenytoin or a similar medication to monitor its levels in your blood. This is particularly useful for adjusting doses, especially in children, elderly patients, or those with liver or kidney issues, to prevent toxicity or insufficient treatment.

How It’s Done

A blood sample is drawn from a vein, typically in your arm. The sample is processed to separate plasma, where the medication concentration is measured using advanced laboratory techniques like high-performance liquid chromatography (HPLC). Results are usually available within 24–48 hours.

What the Results Mean

Results provide a precise measurement of the medication’s concentration in your plasma. While reference ranges vary by lab and patient factors, these levels help guide whether your dose is optimal. Your doctor will interpret the results in the context of your medical history and symptoms.