Single System Double Blinded Trial to Evaluate the Effect of Pre-operative Treatment With DigiFab to Prevent Post-operative Acute Kidney Injury (AKI) in Patients at High Risk for AKI Undergoing Cardiac Bypass Graft Surgery
Phase: PHASE4
Conditions: Acute Kidney Injury
Sponsor: University of Maryland, Baltimore

 
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Pre-operative treatment with DigiFab to prevent post-operative acute  
kidney injury (AKI) in patients at high risk for AKI undergoing cardiac 
bypass graft surgery 
 
April 24, 2022 
 
NCT # HP-00083553 
 
 

 
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1. Introduction 
Acute kidney injury (AKI) occurs in up to 30% of patients undergoing coronary artery bypass 
graft (CABG) surgery1; consequently, renal replacement therapy is often required. In patients 
needing renal replacement therapy, mortality is as high as 60-70%2. There has been a trend to 
operate on higher risk patients3, likely increasing the prevalence of AKI post CABG. With 
roughly four hundred thousand CABG surgeries performed annually in the US4, this represents 
an enormous health care problem. Currently, there is no known therapy for AKI or way to 
prevent AKI occurrence in this patient population. Evidence suggests that elevated preoperative 
circulating endogenous ouabain (EO), a cardiac glycoside structurally similar to digoxin, leads to 
increased risk of AKI post CABG5,6. We propose to study the impact of giving preoperative 
DigiFab, a biological preparation approved by the FDA for the treatment of digitalis toxicity, as 
a means to reduce/prevent the incidence of CABG-evoked AKI.  DigiFab is expected to have a 
beneficial and possibly unique utility in this scenario because the antibodies it contains have the 
side-property of also binding EO with high affinity (Hamlyn & Blaustein, unpublished).  
 
 
2.  Rationale  
Postoperative AKI is one of the most clinically significant causes of morbidity and mortality in 
patients undergoing CABG.3 Even minimal increases in serum creatinine are associated with 
increased mortality7. Similarly, acute renal failure is the strongest risk factor for death in patients 
undergoing cardiac surgery8. Clinical studies indicate that high pre-op plasma EO concentrations 

 
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are a marker for AKI in patients undergoing CABG surgery, and the highest plasma EO 
concentrations are associated with the highest risk and poorest clinical outcomes5,6.  
 
High plasma EO may directly cause renal damage in vivo and in vitro5,9. In cultured rodent renal 
cells, prolonged ouabain treatment has been shown to decrease nephrin expression (a protein 
involved in formation of the glomerular filtration barrier).5 In vivo, prolonged ouabain 
administration decreases renal clearance, increases plasma creatinine, and increases proteinuria. 
Further, Rostafuroxin, a unique, first generation ouabain receptor antagonist, has been shown to 
attenuate the ouabain-evoked renal damage by preventing nephrin down regulation in rats9,10. 
Unfortunately, Rostafuroxin is not currently an FDA approved drug, and the commercial 
prospects for this agent seem minimal because it binds to its in vivo ouabain receptor with 
relatively low affinity11.  
 
The absence of a clinically-useful ouabain receptor antagonist with which to interfere/preempt 
AKI opens the door to other strategies, including the possibility of short-term in vivo 
immunoneutralization.  In this regard, DigiFab is one of several biologicals approved for the 
treatment of digitalis toxicity worldwide.  In the US, DigiFab (BTG, Intl.), which consists 
exclusively of monovalent Fab fragments, was preceded by the divalent Fab preparation, 
Digibind (Wellcome, Glaxo, Smith Kline).  Digibind is no longer commercially available.  Both 
Fab preparations bind and immunoneutralize digoxin as well as other digitalis-like entities, 
including ouabain, with high affinity12,13, but differ in the rates at which their Fab fragments are 
cleared from the circulation.  Like Digibind, DigiFab has proven to be safe and has negligible 
side effects and virtually no toxicity when used at approved doses.14 

 
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Furthermore, several trials using Fab fragment preparations have been conducted recently.  
Among pregnant women with severe pre-eclampsia, both Digibind and DigiFab significantly 
reduced progression of renal dysfunction15,16.  The utility of these preparations in pregnant 
women with severe pre-eclampsia provides further evidence of safety as well as efficacy in 
minimizing the decline in renal function.  
 
Based upon the aforementioned preliminary information, we will test the hypothesis that the 
ability to lower serum EO by immunoneutralization with DigiFab prior to CABG surgery will 
reduce the incidence of post-operative AKI, and thus, reduce post-operative morbidity and 
mortality.  
 
3. Methods 
We plan to conduct a randomized double-blinded study investigating the role of DigiFab in 
patients with elevated risk of acute kidney injury undergoing CABG surgery. Patients who are 
undergoing CABG, meet the inclusion criteria, and provide consent will be enrolled in this study 
and randomized to either DigiFab arm or the placebo (vehicle) arm. The number of patients to be 
consented will be enough to achieve two hundred and fifty evaluable participants. The number 
consented will not be more than 350 patients. The study involves a follow up period of 72 hours 
post CABG surgery.  
 
3A- Recruitment 

 
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All patients awaiting non-emergency CABG surgery will be considered for this study. Patients 
with high risk of developing AKI post CABG will be included in this study. High risk of AKI 
will be defined as one of the following: GFR >15 but below 60 (must be  >36 hours after 
receiving any contrast, but within two weeks of signing consent) or a history of diabetes 
mellitus.2 Diabetes will be defined as a past diagnosis or a current hemoglobin a1c of ≥6.5%.  
 
3B. Inclusion Criteria  
Each patient must meet all the following criteria to be enrolled in this study: 
• Patient provided informed consent 
• Male or female > 18 years of age 
• Undergoing CABG and one of the following: 
o GFR (Cockcroft-Gault) less than 60 (should be > 36 hours after receiving any 
contrast, but within two weeks of signing consent)  
o Past diagnosis of Diabetes or current Hemoglobin A1c of ≥ 6.5% 
 
3C . Exclusion criteria  
A patient who meets any of the following criteria will be excluded from this study: 
• AKI defined as:  
o  Decrease in GFR > 25% of baseline based on RIFLE criteria17 
• Received contrast within the past 36 hours of IP administration 
• Prior kidney transplantation 
• Prior adverse reaction to DigiFab 
• Received Digoxin within the past 30 days 

 
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• Has allergy to papaya, papain, or sheep proteins  
• GFR < 15 (within two weeks of signing consent and > 36 hours after receiving contrast) 
 
Calculation of Creatinine Clearance (CCr; Cockcroft-Gault Formula) 
CCr={((l 40–age) x weight)/(72xSCr)}x 0.85 (if female) 
CCr (creatinine clearance) = mL/minute 
Age = years; Weight = kg 
SCr (serum creatinine) = mg/dL 
 
3D. Enrollment and Baseline 
Patients awaiting surgery in the hospital or having elective surgery and initially seen as out-
patients will be eligible for this study. 
After a participant completes the consent process and is deemed eligible for this study, baseline 
parameters will be obtained. Laboratory tests—including basic metabolic panel (BMP, including 
serum creatinine), NT-pro-BNP (N-terminal prohormone of brain natriuretic peptide), and 
troponin—and hemodynamics – heart rate, blood pressure (systolic, diastolic, and mean arterial 
pressure)—obtained ideally within 24 hours before IP administration will be recorded. If 
multiple values exist within this time frame, the value closest to time of surgery will be used. 
Blood for EO concentrations, Proenkephalin A,18 and TIMP × IGFBP719,20,21 will be drawn prior 
to investigational drug administration. Patient characteristics including age, sex, comorbidities 
(hypertension and diabetes) will be noted. Of note, ouabain concentrations take many days to 
return and will not be known prior to CABG.,  
 

 
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3E. Randomization  
After ensuring eligibility, patients will be randomized by the investigational pharmacy. Stratified 
randomization will be employed using race and sex.  Patients will be randomized approximately 
24 hours prior to surgery. In the event that surgery is postponed to a later date, patients will be 
permitted to remain in the study. Digifab will be re-administered according to the usual protocol. 
If surgery is moved a second time and Digifab had been given, patients will be removed from the 
study.  
 
3F. Intervention  
BTG will provide DigiFab; placebo (saline) will be provided by the pharmacy. In-hospital study 
patients will be dosed intravenously with 80 mg Digifab or an equivalent volume of fluid the 
night prior to surgery (approximately 12-15 hours prior to surgery) and again 1 hour pre-
operatively. The vials will be stored in the hospital investigational pharmacy. Patients being 
admitted to the hospital on the day of surgery will receive 80 mg Digifab or an equivalent 
volume of fluid approximately 1 hour prior to surgery. 
 
3G. Post-operative data:  
We will collect blood for endogenous ouabain, Proenkephalin A, and TIMP × IGFBP7 in the 
immediate post-operative period 0 to 4 hours post-surgery. The ouabain measurement at this time 
will determine the fraction that is free and that which is bound to DigiFab.  This 4 hr post-op 
sample window provides the only opportunity to obtain critical information concerning the 
efficacy of the DigiFab immunoneutralization.  Total serum ouabain, Proenkephalin A, TIMP × 
IGFBP7, and creatinine concentrations will also be obtained at 72 +/- 12 hours post-surgery.  

 
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Time spent on cardiopulmonary bypass will be noted.  Seven days post-operatively, need for any 
type of renal replacement therapy will be recorded. Lastly, mortality within a seven-day period 
will be noted.   
 
3H. Data  collection  
Each variable will be captured and stored in a HIPAA compliant and secure database.  
 
3I. Primary endpoint: Changes in GFR will be compared in patients who receive placebo and 
intervention by ANOVA and, as appropriate, parametric or non-parametric tests. The primary 
endpoint will compare only patients with the 50% highest baseline (preoperative) concentrations 
of ouabain.   
 
3J. Secondary endpoints:  
1. Comparing GFR amongst all patients  
2. Incidence of AKI comparing the groups (25% decrease from baseline) 
3. Incidence of renal replacement therapy by 30 days 
4. Comparing intraoperative and 30 day mortality for placebo vs DigiFab.  
5. In patients on cardiopulmonary bypass for the longest time (top 50%).  
6.  Comparison of change in Proenkephalin A in patients receiving Digifab and placebo. 
7. Comparison of change of TIMP × IGFBP7 in patients receiving Digifab and placebo. 
8. Comparison of GFR in patients receiving one dose and patients receiving two doses of 
Digifab. 
 

 
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3K. Analysis  
Mean comparisons will be made by ANCOVA and, as appropriate, parametric or non-parametric 
tests. Chi square will be used as indicated. We will control for GFR and sex. 
 
3L. Power 
We postulate that the average patient will have a GFR of 50 which correlates to a creatinine of 
129 µmol/l. Previous studies have shown a post-operative mean increase of 48 µmol/l with a 
standard deviation of 76. Therefore, on average, post-operative creatinine should be 177 µmol/l, 
which is roughly a GFR of 35. A trial of 62 patients per group (top half of elevated ouabain 
concentrations) should have a power of >70% to detect a 36 µmol/l difference in plasma 
creatinine, i.e., a creatinine of 141 µmol/l (177-36).  A creatinine of 141 µmol/l correlates to a 
GFR of 45—a ~25% increase in GFR. 
 
4. Risks  
The primary risk associated with this study includes all of the potential adverse effects of 
DigiFab including: anaphylactic and anaphylactoid reactions, delayed allergic reactions, and a 
febrile response to immune complexes formed. However, since the Fab fragment of the antibody 
lacks the antigenic determinants of the Fc region, this should pose a reduced immunogenic 
threat. Of note, no patients during the clinical trials experienced an anaphylactic event. Patients 
with allergies to sheep protein would be at particular risk. In a registry of 717 adult patients 
receiving DigiFab, 6 had a probable or possible adverse reaction to the medication. All were 
symptomatically treated successfully22. Study participants will be monitored closely for potential 
adverse effects in the perioperative, operative, and post-operative setting. If an anaphylactic 

 
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reaction occurs, epinephrine, steroids, an H2 blocker, and diphenhydramine will be given as 
appropriate. Each blood draw carries the risk of pain associated with the venous puncture. As 
this is the first use of DigiFab in this patient population, unknown side effects are possible.  
 
Data Safety and Monitoring Board 
There will be an independent Data Safety and Monitoring Board (DSMB) which will assess the 
safety of the trial after 62 patients (first 25% of patients are enrolled). An unblinded coordinator 
will provide the board with all adverse events and deaths to investigate. The DSM board will 
evaluate the cause of deaths and allergic reactions. The panel will consist of Dr. Libin Wang, Dr. 
Timm Dickfeld, Dr. Chaz Hong, and a statistician.  
 
5.  Benefits  
Study participants may experience short and long-term benefits. Potential benefits include 
prevention of AKI, reduced hospital stay, protection from renal replacement therapy, and 
decreased mortality. In the long term, potential benefits include protection from: progression to 
chronic kidney disease, need for renal replacement therapy and early death.23   
 
6.  Confidentiality 
All data collected will be de-identified once stored on the database. 
 
7.  Consent process  
Study participants who meet  inclusion criteria will be approached by a study coordinator or 
investigator. The consenter will review the risks and benefits to partaking in this trial. If the 

 
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participant expresses interest, a study consent form will be provided. Potential participants will 
have the opportunity to ask questions at any point during the explanation process. 
 
8. Conflict of Interest 
Drs. Gottlieb, Blaustein, and Hamlyn have a provisional patent and a patent pending for the use 
of DigiFab (and/or a ouabain antagonist) to prevent renal dysfunction in patients undergoing 
CABG.  All investigators will be blinded to the treatment received until all data are finalized. 
 
9.  HIPAA Compliance 
All authors have completed HIPPA training in accordance with the University of Maryland. 
 
10.  Stopping Rules 
The study will be halted if the independent data monitoring determines that known or unknown 
side effects of DigiFab are occurring with unacceptable symptoms for the patient and/or 
mortality. The DSMB will determine the specific rules. 
 
11. Timeline 
 
1. Patient consent and enrollment 
2. Prior to administering the first dose of DigiFab, draw blood for NT-pro-BNP, troponin,  
proenkephalin A, TIMP × IGFBP7, and endogenous ouabain (ideally within 24 hours of IP 
administration. Record BMP (including creatinine) values, demographics, and hemodynamics. 

 
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3. For hospitalized patients, approximately 12-15 hr before surgery:  Administer 
DigiFab 80 mg or placebo if > 36 hours post contrast.  If necessary to meet entry requirements, 
only immediate pre-op dose will be given. 
4. One hr pre-op: Administer a second dose (or first dose for same day admissions) of 
DigiFab 80 mg or placebo 
5. Surgery 
6. 0-4 hr Post-op:  Draw blood for free and bound ouabain, proenkephalin A, TIMP × 
IGFBP7 determinations.  Record BMP (including creatinine) values 
7. 72 ± 12 hr post-op:  Draw blood for total ouabain, proenkephalin A, TIMP × IGFBP7.  
Record BMP values (including creatinine). 
8. 30 days-Contact patient, next of kin, or hospital records to ascertain whether patient is 
alive and whether the patient has undergone renal replacement therapy. 
 

 
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