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HelpTest Code SFZ Sulfamethoxazole, Serum
Reporting Name
Sulfamethoxazole, SUseful For
Monitoring sulfamethoxazole therapy to ensure drug absorption, clearance, or compliance
Performing Laboratory
Mayo Clinic Laboratories in Rochester
Specimen Type
Serum RedSpecimen 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 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 |
Reference Values
>50 mcg/mL (Peak)
Day(s) Performed
Monday, Thursday
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 |
Clinical Information
Sulfamethoxazole is a sulfonamide antibiotic that is administered in conjunction with another antibacterial, trimethoprim. These agents are used to treat a variety of infections, including methicillin-resistant Staphylococcus aureus, and for prophylaxis in immunosuppressed patients, such as individuals who are HIV positive.
Therapeutic drug monitoring is not commonly performed unless there are concerns about adequate absorption, clearance, or compliance. Monitoring of sulfamethoxazole is indicated only when prolonged (>3 months) therapy is required.
Sulfamethoxazole is absorbed readily after oral administration, with peak serum concentration occurring 1 to 4 hours after an oral dose. Its average elimination half-life is approximately 10 hours. Toxicity includes crystalluria with resultant calculi and kidney disease. Toxicity is due to a high concentration of acetylated, relatively insoluble forms of the drug. Excess fluid should be taken with sulfamethoxazole to avoid formation of urine sulfonamide crystals.
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.
Report Available
2 to 5 daysReject Due To
| Gross hemolysis | OK |
| Gross lipemia | OK |
| Gross icterus | OK |
Cautions
Specimens collected in serum gel tubes are not acceptable, as the drug can absorb on the gel and lead to falsely decreased concentrations.
Method Name
Liquid Chromatography Mass Spectrometry (LC-MS/MS)
Forms
If not ordering electronically, complete, print, and send a Therapeutics Test Request (T831) with the specimen.