Interference Testing in Therapeutic Drug Monitoring

Transcription

1 Interference Testing in Therapeutic Drug Monitoring Claudio Otoya Hospital Scientist SEALS Department of Clinical Chemistry and Endocrinology New South Wales Health Pathology Prince of Wales Hospital, Sydney

2 Clinical History 9 year old Girl with Cystic Fibrosis Admitted in July 2015 with Pseudomonas aeruginosa infection 2 weeks IV antibiotics and chest physiotherapy Tobramycin & Ceftazidime Tobramycin in therapeutic range Patient remained febrile but well throughout and blood tobramycin levels were taken by finger prick

3 Case study Annual review October 2015 Now on Tobramycin nebuliser No CF related issues November 2015: patient presents with mild persistent cough for 3 weeks Recurrent Pseudomonas infection IV antibiotics 2 days after IV Tobramycin, trough level: 2.1 mg/l (ther. threshold <1.0 mg/l) Tobramycin measurement repeated the following evening before next dose Withhold dose if result is not <1.0 mg/l Repeat Tobramycin measurement remained high at 1.8 mg/l Tobramycin antibiotic was withheld

4 TOBRAMYCIN (mg/l) Chronology of Tobramycin measurements 2.5 Tobra Withheld Kidney Function EUC, CC normal Albumin/Creatinine Ratio Urine Protein negative Urine Blood negative 0 Therapeutic Threshold POW Tobramycin (mg/l)

5 TOBRAMYCIN (mg/l) Chronology of Tobramycin measurements 2.5 Tobra Withheld Kidney Function EUC, CC normal Albumin/Creatinine Ratio Urine Protein negative Urine Blood negative 0 Therapeutic Threshold POW Tobramycin (mg/l)

6 TOBRAMYCIN (mg/l) Chronology of Tobramycin measurements Tobra Withheld Eldemir O, Maciejewski SR, Oermann CM. Falsely elevated serum Tobramycin concentrations in Cystic Fibrosis patients treated with concurrent Intravenous and Inhaled Tobramycin. Paediatric Pulmonology 2000; 29: Therapeutic Threshold POW Tobramycin (mg/l)

7 TOBRAMYCIN (mg/l) Chronology of Tobramycin measurements Tobra Withheld Eldemir O, Maciejewski SR, Oermann CM. Falsely elevated serum Tobramycin concentrations in Cystic Fibrosis patients treated with concurrent Intravenous and Inhaled Tobramycin. Paediatric Pulmonology 2000; 29: Therapeutic Threshold POW Tobramycin (mg/l)

8 TOBRAMYCIN (mg/l) Chronology of Tobramycin measurements 2.5 Tobra Withheld Therapeutic Threshold POW Tobramycin (mg/l)

9 TOBRAMYCIN (mg/l) Chronology of Tobramycin measurements 2.5 Tobra Withheld Therapeutic Threshold POW Tobramycin (mg/l)

10 TOBRAMYCIN (mg/l) Chronology of Tobramycin measurements 2.5 Tobra Withheld Therapeutic Threshold POW Tobramycin (mg/l)

11 TOBRAMYCIN (mg/l) Chronology of Tobramycin measurements 2.5 Tobra Withheld Therapeutic Threshold POW Tobramycin (mg/l)

12 START Eliminate Prepre, pre analytical errors Exogenous vs Endogenous Interferences Exogenous Drugs Amikacin, Kanamycin Collection tube components Test sample additives Transport/storage Clots Carryover contamination Laboratory Investigation Correct patient Assay imprecision/bias Alternate Instrument Alternate reagent Lot Endogenous Haemolysis Lipids Bilirubin Proteins Excessive analyte concentration Antibodies (Heterophile) Immunological Studies IgG, IgA, IgM Rheumatoid Factor Serum protein electrophoresis Immunofixation No Para proteins detected

13 Reaction Monitor Typically, Para proteins precipitate out of solution upon addition of 1 st reagent Increased turbidity causes increased initial absorbance No evidence of initial increase in absorbance on sample reaction monitor High level internal QC monitor Patient Sample monitor

14 Eliminate Prepre, pre analytical errors Exogenous vs Endogenous Interferences Exogenous Drugs Amikacin, Kanamycin Collection tube components Test sample additives Transport/storage Clots Carryover contamination Laboratory Investigation Correct patient Assay imprecision/bias Alternate Instrument Alternate reagent Lot Endogenous Haemolysis Lipids Bilirubin Proteins Excessive analyte concentration Antibodies (Heterophile) Immunological Studies IgG, IgA, IgM Rheumatoid Factor Serum protein electrophoresis Immunofixation No Para proteins detected Cryoglobulins (heat inactivation) Heterophilic Blocking Reagent (scantibodies) 25% w/v PEG Precipitation (globulins?) Immobilised Protein A/G Immunoprecipitation Interference = IgG antibody

15 Eliminate Prepre, pre analytical errors Exogenous vs Endogenous Interferences Exogenous Drugs Amikacin, Kanamycin Collection tube components Test sample additives Transport/storage Clots Carryover contamination Laboratory Investigation Correct patient Assay imprecision/bias Alternate Instrument Alternate reagent Lot Endogenous Haemolysis Lipids Bilirubin Proteins Excessive analyte concentration Antibodies (Heterophile) Alternate Method Abbott Architect - Particle Enhanced Turbidimetric Inhibition Immunoassay (PETINIA) Cobas Integra 800 Fluorescent Polarisation Immunoassay (FPIA) Immunological Studies IgG, IgA, IgM Rheumatoid Factor Serum protein electrophoresis Immunofixation No Para proteins detected Cryoglobulins (heat inactivation) Heterophilic Blocking Reagent (scantibodies) 25% w/v PEG Precipitation (globulins?) Immobilised Protein A/G Immunoprecipitation Interference = IgG antibody

16 Method Comparisons Roche Cobas 6000 c501 (EMIT) SEALS - POWH Abbott Architect c8000 (PETINIA) PaLMs - RNSH Roche Cobas Integra 800 (FPIA) Douglas Hanly Moir Competitive assay Polyclonal Sheep Ab Tracer = enzyme-labelled Tobramycin Rate assay Measurand = increased enzyme activity Tobramycin a = 1.5 mg/l Tobramycin b = 1.3 mg/l Tobramycin c = 1.3 mg/l Tobramycin d = 0.7 mg/l Competitive assay Monoclonal Mouse Ab Tracer = Tobramycin-coated microparticles Rate assay Measurand = increased rate of agglutination Tobramycin a = 2.06 mg/l Tobramycin b = 1.8 mg/l Competitive assay Monoclonal Mouse Ab Tracer = fluorescein-labelled Tobramycin derivative End-point assay Measurand = decreased fluorescent light emission Tobramycin c = 0.0 mg/l Tobramycin d = 0.0 mg/l

17 IgG antibody against what? What kind of antibody interference could it be Heterophile Antibody Human anti-animal antibody (HAAA) Human anti-mouse antibody (HAMA) Bridging Antibody Anti-tobramycin Antibody

18 2.5 Chronology of Tobramycin measurements at SEALS Pseudomonas Infection - IV Tobramycin Low Dose Tobramycin Nebuliser Pseudomonas Infection - IV Tobramycin Colistin Nebuliser Flu vaccine Pseudomonas Infection - IV Tobramycin Low Dose Tobramycin Nebuliser Pseudomonas Infection - IV Tobramycin Therapeutic threshold Date POWH Tobramycin (mg/l)

19 Competitive EMIT = serum tobramycin

20 Competitive EMIT

21 Anti-Tobramycin Antibody False negative

22 Competitive PETINIA = serum tobramycin

23 Competitive PETINIA

24 Competitive PETINIA

25 (PETINIA) Anti-Tobramycin Antibody? False Negative

26 Competitive FPIA = serum tobramycin Fluorescein molecule bound to tobramycin spins rapidly scattering the fluorescent emitted light, decreasing signal absorbance Fluorescein bound antibody rotate more slowly allows for increased polarised emitted fluorescent light

27 (FPIA) Anti-Tobramycin Antibody = serum tobramycin again should produce a false negative

28 Thank you

29 Roche Cobas 6000 c501 Based on a homogenous enzyme immunoassay technique Competitive assay: Drug in sample vs drug labelled with enzyme (G6PDH) Enzyme activity decreases upon binding to antibody in reagent Measurand = increased enzyme activity () () Reagent anti-tobramycin antibody = polyclonal sheep antibody G6PDH Tobramycin

30 Mimics serum tobramycin scenario

31 Bridging Antibody Interference

32 Interfering antibody

33 Anti-Tobramycin Antibody

34 PETINIA Anti-Tobramycin Antibody = serum tobramycin

35 (PETINIA) Anti-Tobramycin Antibody? = serum tobramycin

36 Tobramycin Aminoglycoside antibiotic narrow therapeutic index Ototoxic - cause hearing loss, damage to the balance system in the inner ear Usually irreversible Nephrotoxic cause damage to tissues of the kidney with long-term use Multiple doses accumulate over course of treatment During sleep urine kidney concentration (tubular reabsorption) To prevent these side-effects: Parenteral Tobramycin needs to be carefully dosed by body weight Amount of Tobramycin in the blood is routinely measured and adjusted accordingly 24 hour daily dose - trough level < 1.0 mg/l to prevent accumulated exposure Tobramycin does not pass the gastro-intestinal tract, so for systemic use it can only be given intravenously or intramuscularly Ophthalmic and nebulised formulations - both have low systemic absorption. Nebulised formulation is indicated in the treatment of exacerbations of chronic infection with Pseudomonas aeruginosa in patients diagnosed with CF Tobramycin is preferred over gentamicin for Pseudomonas aeruginosa pneumonia due to better lung penetration

37 [Tobramycin] mg/l Chronology of Tobramycin measurements POW Tobramycin Level (mg/l) Terapeutic threshold 0.5 0

38 Medications Tobramycin nebulised BD Augmentin Duo BD PO Creon units with each meal (Pancreatic enzyme replacement) Ciprofloxacin BD alter serum levels of antiepileptic drugs (e.g. phenytoin) Omeprazole PO proton pump inhibitor elevates plasma methotrexate levels Azithromycin PO Vit-Ab-DECK PO (multi-vitamin capsule) Vitamin D 2 capsules daily PO N-Acetylcysteine 1 capsule daily PO commenced by patient s family Tumeric capsule 1 capsule daily PO commenced by patient s family Pulmozyme nebulised noct. (rhdnase enzyme)

39 Immunological studies Patient sample collected a month later (December) Tobramycin = 1.3 mg/l IgG = g/l ( g/l) IgM = 1.21 g/l ( g/l) IgA = 1.79 g/l ( g/l) (RF) < 10.6 IU/mL (<20IU/mL) Serum protein electrophoresis & immunofixation no paraprotein detected

40 Further Investigation Tobramycin-coated microparticles from PETINIA method can be utilised to immunoprecipitate potential anti- Tobramycin antibodies No effect on patient s sera no evidence of anti- Tobramycin antibody

41 PEG precipitation DHM sample sent to SEALS Tobramycin re-measured = 1.3 mg/l Immuno-metric interference confirmed Sample treated with 25% w/v Poly-Ethylene Glycol (PEG 6000) Sample spun down Supernatant re-measured = 0.0 mg/l Control Tobramycin patient run with patient sample = 84% recovery No evidence of major co-precipitation of Tobramycin with PEG Two other samples from patient were re-measured after PEG precipitation Pre-PEG = 1.4 mg/l Post-PEG = 0.0 mg/l Pre-PEG = 0.7 mg/l Post-PEG = 0.0 mg/l Interference is macromolecule (>100kDa) most likely an Immunoglobulin

42 Heterophilic Blocking reagent Heterophilic blocking tube (HBT) Scantibodies Composed of specific binders which inactivate heterophilic antibodies Sample from the 17 th Nov (1.4 mg/l) treated with HBT No change

43 What kind of immunoglobulin? Antibody binding proteins Protein A Protein G Bacterial cellular wall proteins which bind to constant region of antibodies Specific for most IgG subclasses of humans, mouse, goat, sheep, cows, pigs

44 Immunoprecipitation Protein A/G resin Agarose beads bound to immobilised protein A/G After incubation antibody (IgG) bound to immobilised protein A/G After centrifugation supernatant cleared of IgG Remove/Further identify the immuno-interference

45 Determine the effective sample to resin ratio to clear IgG from serum Method? Serum protein EPG anything 1:1 sample to resin Later nephelometric measurements of IgG showed 1:3 sample : resin completely clears IgG from serum sample Post protein A/G treatment Tobramycin = 0.0mg/L Control Tobramycin patient remeasured >50% recovery post protein A/G treatment IgG ban d Interference = IgG antibody Contr ol 4: 1 3: 2 1:1 2: 3 1:4 NEAT

46 AUC dosing for Tobramycin AUC therapeutic drug monitoring requires a pair of blood samples 2-3 hours and 6-8 hours post dose: For Cystic Fibrosis/Non CF Bronchiectasis after DOSE ONE and then as recommended by the clinical pharmacist in consultation with respiratory team. For all other indications after DOSE ONE or TWO if course is to continue for 5 or more days After 7 days, recheck 2 hour and 6 hour post dose levels (to recalculate AUC) as well as renal function to ensure clearance has not changed. Weekly urine dipstick for proteinuria is also required. Consider audiology in patients who are likely to receive prolonged/repeated courses of aminoglycosides. Your Clinical Pharmacist is available for advice on all dose adjustments.

47 Anti-Tobramycin Antibody False negative

48