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 Field Name  Data Description
Test Name  Zonisamide
Code  Zonisamide Level.
CPT Code  80203
Last Modified  7/16/2018 2:11:00 PM
Test Name  Zonisamide.
Synonyms  Zonegran, Quantitative
Patient Preparation  
Spec. Requirements  Blood
Tube  Red or Lavender(EDTA)
Collection Volume  4.0 mL Red or 2.0 mL Lavender
Storage  Ambient, Refrigerated or Frozen 14 Days
Routine TAT  
Days Test Performed  
Performed by BHS  None
See Availability  
Reference Lab  LabCorp of America
Reference Lab Code  007915 Zonisamide (Zonegran), Serum
Clinical Use  Monitor drug levels for optimal therapy. Zonisamide is an antiepileptic drug belonging to sulfonamideclass and is chemically unrelated to other antiepileptic drugs. While the exact mechanism of action is unknown, anticonvulsant activity maybe mediated by action at sodium and calcium channels. This action may result in stabilizingneuronal membranes and suppressing neuronal hypersynchroni- zations. Preliminary studies on smaller population groups has indicated possible other uses for zonisamide in intractable neuropathic pain syndromes and refractory migraine headaches. Zonisamide is excreted primarily in urine as the parent drug and glucuronide of the metabolite 2-sulfamoylacetyl phenol. Metabolism of zonisamide is mediated by the P450 isozyme CYP3A4 and to a lesser extent by CYP2D6. The drug is rapidly absorbed orally following200-400 mg doses in volunters. Peak plasma concentrations were 2-5 ug/mL and occurred in 2-6 hours. Food does not effect the overall bioavailability, but delays time to maximum concentration until 4-6 hours. Zonisamide extensively binds to erythrocytes, resulting in an 8-fold higher concentration in red blood cells than in plasma. Thepharmacokinetics of zonisamide are dose proportional in the range of 200-400 mg. Time to steady state is from 5-15 days with an elimination half-life of 63-69 hours in volunteers receiving no other medication. The half-life however, is reduced by the comedicated P-450 inducers phenytoin and carbamazepine. The half-life of zonisamide isreduced to a mean of 27.1 hours when the former is co-administered and to a mean of 36.4 hours with co-administration of the latter.
Reference Range  10.0-40.0 mg/mL
Critical Value  
Testing Sample Type  Serum or Plasma
Min Lab Testing Volume  0.4 mL (NOTE: This volume does not allow for repeat testing)
Special Handling  DO NOT USE A GEL-BARRIER TUBE. The use of gel-barrier tubes is not recommended due to slow absorption of the drug by the gel. Depending on the specimen volume and storage time, the decrease in drug level due to absorption may be clinically significant.
Lab Notes  Collection: Serum must be separated from cells within 45 minutes of collection and transferred to a plastic transport tube. Plasma must be separated from whole blood immediately and transferred to a plastic transport tube for shipment to the laboratory. Trough: Immediately prior to next dose. Steady-state levels are reached within 5-15 days in patients on zonisamide monotherapy. Causes for rejection: Use of gel-barrier tube; hemolyzed sample; non-separated serum or plasma sample
Methodology  LC/MS-MS - Liquid Chromatography/Tandem Mass Spectrometry
Limitations  Zonisamide is contraindicated in patients who have demon- strated hypersensitivity to sulfonamides or zonisamide. Consideration should be given to discontinuing zonisamide inpatients who develop an otherwise unexplained rash. If the drug is not discontinued, patients should be observed frequently.

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