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HelpTest ID: POSA Posaconazole, Serum
Reporting Name
Posaconazole, SUseful For
Monitoring posaconazole therapy
Specimen Type
Serum RedSpecimen Required
Supplies: Sarstedt Aliquot Tube, 5 mL (T914)
Collection Container/Tube: Red top (serum gel/SST are not acceptable)
Submission Container/Tube: Plastic vial
Specimen Volume: 2 mL
Collection Instructions: Within 2 hours of collection, centrifuge, and aliquot serum into plastic vial.
Specimen Minimum Volume
0.6 mL
Specimen Stability Information
| Specimen Type | Temperature | Time | Special Container |
|---|---|---|---|
| Serum Red | Refrigerated (preferred) | 28 days | |
| Ambient | 28 days | ||
| Frozen | 28 days |
Reference Values
>700 ng/mL (trough)
Day(s) Performed
Monday through Saturday
Test Classification
This test was developed and its performance characteristics determined by Mayo Clinic in a manner consistent with CLIA requirements. It has not been cleared or approved by the US Food and Drug Administration.CPT Code Information
80187
LOINC Code Information
| Test ID | Test Order Name | Order LOINC Value |
|---|---|---|
| POSA | Posaconazole, S | 53731-6 |
| Result ID | Test Result Name | Result LOINC Value |
|---|---|---|
| 89591 | Posaconazole, S | 53731-6 |
Clinical Information
Posaconazole interferes with fungal cytochrome P450 (CYP) lanosterol-14 alpha demethylase activity, thereby decreasing synthesis of ergosterol, the principal sterol in fungal cell membrane, and inhibiting fungal cell membrane formation.(1,2)
Posaconazole has been approved for prophylaxis of invasive Aspergillus and Candida infections in severely immunocompromised patients (eg, hematopoietic stem cell transplant recipients with graft-versus-host disease [GVHD] or those with prolonged neutropenia secondary to chemotherapy for hematologic malignancies) and treatment of oropharyngeal candidiasis (including patients refractory to itraconazole or fluconazole).(1,3) It also is approved for ocular administration (drug monitoring not required for this use).
Posaconazole has a variable absorption. Food and liquid nutritional supplements increase absorption, and fasting states do not provide sufficient absorption to ensure adequate plasma concentrations.(4,5) The drug has a high volume of distribution (Vd=465-1774 L) and is highly protein bound (≥97%), predominantly to albumin.(1,3) The drug does not undergo significant metabolism; approximately 15% to 17% undergoes non-CYP-mediated metabolism, primarily via hepatic glucuronidation into metabolites.(1) The half-life elimination is approximately 35 hours (range: 20-66 hours); steady state is achieved after about 5 to 7 days. Time to maximum concentration is approximately 3 to 5 hours, but due to the highly variable absorption, trough level monitoring is recommended.
Therapeutic drug monitoring should be considered in the following situations:
-To document optimal absorption when used for prophylaxis or active treatment of a fungal infection
Consider rechecking a level even if initial level was in the goal range if the patient:
-Is unable to meet optimal nutritional intake
-Is receiving continuous tube feeding
-Is receiving a proton pump inhibitor (decreased posaconazole levels in some studies)
-Has mucositis, diarrhea, vomiting, GVHD, or other reason that the drug may not be absorbed well
Interpretation
Levels greater than 700 ng/mL (0.7 mcg/mL) have been suggested for prophylaxis.
Levels greater than or equal to 1250 ng/mL (1.25 mcg/mL) were shown to be optimal in a salvage trial for treatment of invasive Aspergillus infections.
A toxic range has not been established.
Clinical Reference
1. Noxafil (posaconazole). Package insert: Schering Corporation; 2006
2. Goodman and Gilman's: The Pharmacological Basis of Therapeutics. 10th ed. McGraw-Hill Professional; 2001
3. Physicians' Desk Reference (PDR). 61st ed. Thomson PDR; 2007
4. Courtney R, Wexler D, Radwanski E, Lim J, Laughlin M. Effect of food on the relative bioavailability of two oral formulations of posaconazole in healthy adults. Br J Clin Pharmacol. 2004;57(2):218-222. doi:10.1046/j.1365-2125.2003.01977.x
5. Courtney R, Radwanski E, Lim J, Laughlin M. Pharmacokinetics of posaconazole coadministered with antacid in fasting or nonfasting healthy men. Antimicrob Agents Chemother. 2004;48(3):804-808. doi:10.1128/AAC.48.3.804-808.2004
6. Milone MC, Shaw LM: Therapeutic drugs and their management. In: Rifai N, Chiu RWK, Young I, Burnham CAD, Wittwer CT, eds. Tietz Textbook of Laboratory Medicine. 7th ed. Elsevier; 2023:420-453
Report Available
2 to 5 daysMethod Name
Liquid Chromatography-Tandem Mass Spectrometry (LC-MS/MS)
Forms
If not ordering electronically, complete, print, and send a Therapeutics Test Request (T831) with the specimen.
| mml-antifungals, mml-drugmonitoring |