Therapeutic drug monitoring of eculizumab
|Test Id||Reporting Name||Available Separately||Always Performed|
|C5FX||C5 Complement, Functional, S||Yes||Yes|
|C5AG2||C5 Complement, Antigen, S||Yes, (Order C5AG)||Yes|
C5FX: Automated Liposome Lysis Assay
Patient Preparation: Fasting preferred
Supplies: Aliquot Tube, 5 mL (T465)
Specimen Type: Serum
Collection Container/Tube: Red top
Submission Container/Tube: Plastic vial
Specimen Volume: 1.5 mL
1. Recommended timeframe for the blood collection is a trough, or immediately prior to next intravenous infusion.
2. Immediately after specimen collection, place the tube on wet ice.
3. Centrifuge and aliquot serum into plastic vial.
4. Freeze specimen within 30 minutes.
If not ordering electronically, complete, print, and send 1 of the following forms with the specimen:
-Renal Diagnostics Test Request (T830)
-Coagulation Test Request (T753)
-Therapeutics Test Request (T831)
|Specimen Type||Temperature||Time||Special Container|
|Serum Red||Frozen (preferred)||14 days|
Therapeutic drug monitoring of eculizumab
Eculizumab (Soliris, Alexion Pharmaceuticals) is a humanized hybrid monoclonal antibody (IgG2/IgG4) that blocks complement C5 cleavage, thereby preventing the activation of the proinflammatory effects of C5a and the cytolytic effects of the membrane attack complex (MAC) formed by C5b-C9. It is US Food and Drug Administration approved for atypical hemolytic uremic syndrome(1) and paroxysmal nocturnal hemoglobinuria,(2) and it is also prescribed for other conditions such as C3 glomerulopathies.(3) The dosing regimen for an average adult may vary from 300 to 1200 mg intravenously every 2 weeks during the maintenance stages, according to the condition for which the drug is prescribed. Therapy efficacy may be monitored by measuring efficiency of complement blockade.(4) Eculizumab will affect complement function assays that rely on the formation of the MAC to generate cell lysis. Although total complement and soluble MAC have been recommended for eculizumab monitoring, the measurement of C5 function and C5 antigen more specifically indicate the impact of eculizumab on the complement system blockage and may help guide the next dose of the drug.
This panel measures the pharmacodynamics effects of eculizumab on the complement system.
C5 COMPLEMENT ANTIGEN
C5 COMPLEMENT FUNCTIONAL
The panel will measure the pharmacodynamic effects of eculizumab on the complement system. Total complement function, alternative pathway function, and C5 function assays will be decreased to a similar extent in the presence of eculizumab. The function of C5 may be completely absent when eculizumab is present at therapeutic concentrations. C5 antigen, on the other hand, will be normal or elevated. C5 complement function drops on average 30% with 25 mcg/mL of eculizumab, and 70% with 50 mcg/mL. In the presence of 100 mcg/mL of eculizumab in serum, there is on average 20% residual C5 function.
Decreased C5 function in the presence of normal or elevated C5 antigen concentrations suggests eculizumab is partially blocking C5 activity.
Absent C5 function in the presence of normal or elevated C5 antigen concentrations suggests eculizumab is completely blocking C5 activity.
Normal C5 function in the presence of normal or elevated C5 antigen concentrations suggests eculizumab concentration is not sufficient to block C5 activity.
If C5 function and C5 antigen concentrations are all decreased, it may be due to a secondary consumption process, poor hepatic synthesis of complement proteins or C5 deficiency. Clinical correlation recommended. If indicated, resubmit samples to confirm results.
In a Mayo Clinic study with samples from individual subjects with normal complement activity defined by the total complement (CH50) assay and spiked with varying concentrations of eculizumab,(5) there was a significant decrease in CH50, alternative pathway function, and C5 functional results with eculizumab. Considering that the therapeutic target concentrations are expected to be above 50 mcg/mL, the results showed that eculizumab is partially blocking the complement cascade at 25 mcg/mL, with a complete blockage for C5 functional at 100 mcg/mL.
1. Wong EK, Goodship TH, Kavanagh D: Complement therapy in atypical haemolytic uraemic syndrome (aHUS). Mol Immunol. 2013;56:199-212
2. Rother RP, Rollins SA, Mojcik CF, Brodsky RA, Bell L: Discovery and development of the complement inhibitor eculizumab for the treatment of paroxysmal nocturnal hemoglobinuria. Nat Biotechnol. 2007;25:1256-1264
3. Zuber J, Le Quintrec M, Krid S, et al: Eculizumab for atypical hemolytic uremic syndrome recurrence in renal transplantation. Am J Transplant. 2012;12:3337-3354
4. Volokhina EB, van de Kar NC, Bergseth G, et al: Sensitive, reliable and easy-performed laboratory monitoring of eculizumab therapy in atypical hemolytic uremic syndrome. Clin Immunol. 2015;160(2):237-243
5. Andreguetto B, Murray D, Snyder M, et al: The impact of eculizumab in complement assays. Mol Immunol. 2015;67:119-120
6. Willrich MAV, Braun KMP, Moyer AM, Jeffrey DH, Frazer-Abel A. Complement testing in the clinical laboratory. Crit Rev Clin Lab Sci. 2021 Nov;58(7):447-478. doi: 10.1080/10408363.2021.1907297
Functional C5 complement
C5 activity is measured by mixing patient serum with a C5-deficient serum. The lytic activity of the serum mixture is tested against sensitized, labeled liposomes. If lysis occurs, the patient serum must be the source of the C5. The target liposomes are a commercial reagent.(Unpublished Mayo method)
Anti-C5 reagent is added to patient serum and quantitated on a Siemens BN II analyzer by fixed-time kinetic nephelometry.(Unpublished Mayo method)
Monday through Friday
This test was developed, and its performance characteristics determined by Mayo Clinic in a manner consistent with CLIA requirements. This test has not been cleared or approved by the US Food and Drug Administration.
|Test Id||Test Order Name||Order LOINC Value|
|ECUMP||Eculizumab Monitoring Panel, S||In Process|
|Result Id||Test Result Name||
Result LOINC Value
Applies only to results expressed in units of measure originally reported by the performing laboratory. These values do not apply to results that are converted to other units of measure.
|C5FX||C5 Complement, Functional, S||60472-8|
|C5AG2||C5 Complement, Antigen, S||4505-4|