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24999 Sulfamethoxazole, Serum (SFZ)

Sulfamethoxazole, Serum (SFZ)
Test Code: SULFASO
Synonyms/Keywords
​Bactrim (order both tests), Bactrim (Sulfamethoxazole and trimethoprim), Gantanol (Sulfamethoxazole), SEPTRA (Sulfamethoxazole and Trimethoprim), Sulfamethoxazole, Sulfamethoxazole and Trimethoprim (Bactrim, SEPTRA), Trimethoprim and Sulfamethoxazole (Bactrim, SEPTRA)
Useful For
Monitoring therapy to ensure drug absorption, clearance, or compliance
Specimen Requirements
Specimen Type Preferred Container/Tube Acceptable Container/Tube Specimen Volume Specimen Minimum Volume
(allows for 1 repeat)
Pediatric Minimum Volume
(no repeat)
Serum​ ​Red Top Tube (RTT) 1 mL​ ​0.2 mL
Collection Processing Instructions
1. Serum for a peak level should be drawn 60 minutes after dose.
2. Spin down within 2 hours of draw.
Specimen Stability Information
Specimen Type Temperature Time
​Serum Refrigerated (preferred)​ ​28 days
​Ambient ​28 days
​Frozen ​28 days
Rejection Criteria
​Other ​Serum gel tube
Interference

​Specimens collected in serum gel tubes are not acceptable, as the drug can absorb on the gel and lead to falsely decreased concentrations. 

Performing Laboratory Information
Performing Location Day(s) Test Performed Analytical Time Methodology/Instrumentation
Mayo Clinic Laboratories​​ ​Monday, Thursday ​2 days
Liquid-Chromatography Tandem Mass Spectrometry (LC-MS/MS)
Reference Lab
Test 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 HIV-positive individuals. 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 2 to 3 hours after an oral dose. Its average elimination half-life is 6 to 10 hours. Toxicity includes crystalluria with resultant calculi and renal disease.  Toxicity is due to high concentration of acetylated, relatively insoluble forms of the drug. Excess fluid should be taken with sulfamethoxazole to avoid formation of urine sulfonamide crystals. 
Reference Range Information
Performing Location Reference Range
Mayo Clinic Laboratories​​
>50 mcg/mL
Interpretation
Serum drug concentrations should be interpreted with respect to the minimum inhibitory concentration (MIC) of targeted organisms. Most patients will display peak steady-state serum concentrations >50 mcg/mL when drawn at least 1 hour after an oral dose. Targets 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 >125 mcg/mL.
Outreach CPTs
CPT Modifier
(if needed)
Quantity Description Comments
​80299
Synonyms/Keywords
​Bactrim (order both tests), Bactrim (Sulfamethoxazole and trimethoprim), Gantanol (Sulfamethoxazole), SEPTRA (Sulfamethoxazole and Trimethoprim), Sulfamethoxazole, Sulfamethoxazole and Trimethoprim (Bactrim, SEPTRA), Trimethoprim and Sulfamethoxazole (Bactrim, SEPTRA)
Ordering Applications
Ordering Application Description
​Centricity ​Sulfamethoxazole, Serum (8238)
​Cerner None​
If the ordering application you are looking for is not listed, contact your local laboratory for assistance.
Specimen Requirements
Specimen Type Preferred Container/Tube Acceptable Container/Tube Specimen Volume Specimen Minimum Volume
(allows for 1 repeat)
Pediatric Minimum Volume
(no repeat)
Serum​ ​Red Top Tube (RTT) 1 mL​ ​0.2 mL
Collection Processing
1. Serum for a peak level should be drawn 60 minutes after dose.
2. Spin down within 2 hours of draw.
Specimen Stability Information
Specimen Type Temperature Time
​Serum Refrigerated (preferred)​ ​28 days
​Ambient ​28 days
​Frozen ​28 days
Rejection Criteria
​Other ​Serum gel tube
Interference

​Specimens collected in serum gel tubes are not acceptable, as the drug can absorb on the gel and lead to falsely decreased concentrations. 

Useful For
Monitoring therapy to ensure drug absorption, clearance, or compliance
Reference Range Information
Performing Location Reference Range
Mayo Clinic Laboratories​​
>50 mcg/mL
Interpretation
Serum drug concentrations should be interpreted with respect to the minimum inhibitory concentration (MIC) of targeted organisms. Most patients will display peak steady-state serum concentrations >50 mcg/mL when drawn at least 1 hour after an oral dose. Targets 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 >125 mcg/mL.
For more information visit:
Performing Laboratory Information
Performing Location Day(s) Test Performed Analytical Time Methodology/Instrumentation
Mayo Clinic Laboratories​​ ​Monday, Thursday ​2 days
Liquid-Chromatography Tandem Mass Spectrometry (LC-MS/MS)
Reference Lab
For billing questions, see Contacts
Outreach CPTs
CPT Modifier
(if needed)
Quantity Description Comments
​80299
For most current information refer to the Marshfield Laboratory online reference manual.