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Leflunomide (Arava®) is a pyrimidine synthesis inhibitor used in the treatment of active rheumatoid arthritis. The drug is available in oral doses containing 10, 20, or 100 mg of active drug. Arava® is an isoxazole immunodulatory agent which inhibits dihydroorotate dehydrogenase (an enzyme involved in de novo pyrimidine synthesis) and has antiproliferative activity. Following oral administration, leflunomide is metabolized to an active metabolite, A77-1726 (teriflunomide), which is responsible for essentially all of its activity in vivo. Peak levels of this metabolite occurred 6 to 12 hours after dosing, with a long half-life (about two weeks).
Liquid chromatography/tandem mass spectrometry (LC/MS-MS)
0.5 mL (Note: This volume does not allow for repeat testing.)
Red-top tube. 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.
Serum must be separated from cells within 45 minutes of collection and transferred to a plastic transport tube. To avoid delays in turnaround time when requesting multiple tests on frozen samples, please submit separate frozen specimens for each test requested.
Causes for Rejection
Serum separator tube; nonfrozen sample; gel-barrier tubes
|Order Code||Order Code Name||Order Loinc||Result Code||Result Code Name||UofM||Result LOINC|
|070021||Leflunomide Metabolite (ARAVA)||38901-5||070022||Leflunomide Metabolite (ARAVA)||ng/mL||38901-5|