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# A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
Sulfamethoxazole, Serum (SFZ)
Test Code: SULFASO
Synonyms/Keywords
​Lab Ref Code:  8238, 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)​ ​14 days
​ ​Ambient ​14 days
​ ​Frozen ​14 days
Rejection Criteria
Hemolysis
Mild OK; Gross reject
​Lipemia
Mild OK; Gross reject
Icterus​
Mild OK; Gross reject
​Other ​Serum gel tube
Performing Laboratory Information
Performing Location Day(s) Test Performed Analytical Time Methodology/Instrumentation
Mayo Medical Laboratories​​ ​ ​
High-Performance Liquid Chromatography (HPLC)
Reference Lab
Mayo Clinic Laboratories
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.
​
Reference Range Information
Performing Location Reference Range
Mayo Medical 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.
 
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
​Lab Ref Code:  8238, 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 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)​ ​14 days
​ ​Ambient ​14 days
​ ​Frozen ​14 days
Rejection Criteria
Hemolysis
Mild OK; Gross reject
​Lipemia
Mild OK; Gross reject
Icterus​
Mild OK; Gross reject
​Other ​Serum gel tube
Useful For
Monitoring therapy to ensure drug absorption, clearance, or compliance
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.
​
Reference Range Information
Performing Location Reference Range
Mayo Medical 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.
 
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 Medical Laboratories​​ ​ ​
High-Performance Liquid Chromatography (HPLC)
Reference Lab
Mayo Clinic Laboratories
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.