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HelpTest Code POSA Posaconazole, Serum
Reporting Name
Posaconazole, SUseful For
Monitoring posaconazole therapy
Method Name
Liquid Chromatography-Tandem Mass Spectrometry (LC-MS/MS)
Performing Laboratory
Mayo Clinic Laboratories in Rochester
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 |
Reject Due To
| Gross hemolysis | OK |
| Gross lipemia | OK |
| Gross icterus | OK |
Reference Values
>700 ng/mL (trough)
Day(s) Performed
Monday through Saturday
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.
Cautions
No significant cautionary statements
Method Description
Posaconazole is extracted by mixing serum samples with acetonitrile to precipitate proteins. The supernatant is removed and analyzed by a liquid chromatography tandem mass spectrometry method.(Unpublished Mayo method)