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Test Code Billings Clinic: 8423 Mayo: SFZ Sulfamethoxazole, Serum

Reporting Name

Sulfamethoxazole, S

Performing Laboratory

Mayo Clinic Laboratories in Rochester

Useful For

Monitoring sulfamethoxazole therapy to ensure drug absorption, clearance, or compliance

Method Name

Liquid Chromatography Mass Spectrometry (LC-MS/MS)


Specimen Required


Supplies: Sarstedt Aliquot Tube, 5 mL (T914)

Collection Container/Tube: Red top (gel tubes/SST are not acceptable)

Submission Container/Tube: Plastic vial

Specimen Volume: 1 mL

Collection Instructions:

1. Serum for a peak level should be collected 60 minutes after dose.

2. Within 2 hours of collection, centrifuge and aliquot serum into a plastic vial.


Specimen Type

Serum Red

Specimen Minimum Volume

0.5 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

>50 mcg/mL (Peak)

Interpretation

Peak concentrations of sulfamethoxazole should be obtained 1 hour after the end of an intravenous dose or 2 to 3 hours after an oral dose, while peak concentrations of trimethoprim can be collected at least 1 hour after an oral dose. Serum drug concentrations should be interpreted with respect to the minimal inhibitory concentration of targeted organisms. Most patients will display peak steady-state serum concentrations greater than 50 mcg/mL when collected at least 1 hour after an oral dose. Target concentrations may be higher, depending on the intent of therapy.

 

For Pneumocystis carinii pneumonia (PCP pneumonia), peak concentrations: 100-150 mcg/mL

Toxicity: >200 mcg/mL

Toxicity (formation of urinary crystals) associated with sulfamethoxazole occurs with prolonged exposure to serum concentrations greater than 125 mcg/mL.

 

Trimethoprim: Most patients will display peak steady-state serum concentrations of more than 2.0 mcg/mL when the specimen is collected at least 1 hour after an oral dose. Target concentrations may be higher depending on the intent of therapy.

Day(s) Performed

Monday, Thursday

Report Available

2 to 5 days

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

80299

LOINC Code Information

Test ID Test Order Name Order LOINC Value
SFZ Sulfamethoxazole, S 10342-4

 

Result ID Test Result Name Result LOINC Value
8238 Sulfamethoxazole, S 10342-4

Forms

If not ordering electronically, complete, print, and send a Therapeutics Test Request (T831) with the specimen.