Plasma and Tissue Concentration of Cefazolin in Preoperative Prophylaxis in Patients Undergoing Bariatric Surgery
Conditions: Bariatric Sleeve Gastrectomy, Cefazolin
Sponsor: Laval University

 
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PLASMA AND TISSUE CONCENTRATION OF CEFAZOLIN FOR 
PREOPERATIVE PROPHYLAXIS IN PATIENTS UNDERGOING 
BARIATRIC SURGERY 
 
 
 
 
Principal Investigators:  
 
Dr. Philippe Gervais, MD 
Microbiologist-Infectiologist 
Department of Microbiology-Infectiology and Immunology 
 
Dr. François Julien, MD 
General surgeron, 
Department of Surgery 
 
 
 
Co-Investigators: 
 
Dr. Laurent Biertho, MD 
Dr. Léonie Bouvet-Bouchard, MD 
Dr. André Tchernof, PhD. 
Mrs. Isabelle Giroux, MSc Pharm 
Dr. Jérôme Laflamme, MD (résident) 
Dr. Michel Ménassa, MD (résident) 
 
 
 
 
 
VERSION 1.0 - O1NOV2017 
VERSION 2.0 - 18APR2018 
VERSION 3.0 - 08APR2019 
 
 
 

 
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BACKGROUND 
 
The growing obesity pandemic is a major public health issue. According to the World 
Health Organization (WHO), global obesity prevalence (BMI ≥ 30 kg/m²) affects about 
650 million individuals. (1) In the U.S. (2014), 37.7% of the population was obese, with 
7.7% of men and 9.9% of women classified as morbidly obese (BMI ≥ 35 kg/m²). (2) In 
Canada (2013), obesity prevalence was 22% in men and 20% in women. (3) 
 
Obesity is associated with multiple comorbidities, including hypertension, coronary artery 
disease, type 2 diabetes, osteoarthritis, obstructive sleep apnea, and non-alcoholic fatty 
liver disease. Overweight (BMI ≥ 25 et < 30 kg/m2) and obesity contributed to 
approximately 3.4 million deaths worldwide in 2010. (4) Bariatric surgery is an effective 
intervention for patients who fail conservative treatments, with over 100,000 procedures 
performed in North America in 2011. (5) 
 
Surgical site infections (SSIs) significantly increase morbidity, mortality, hospital stay, and 
healthcare costs. (6) Reported SSI rates in bariatric surgery range from 1–20%, with 
laparoscopic approaches reducing infection risk. (7-11) Preoperative antibiotic prophylaxis 
administered within 60 minutes before incision is recommended. Cefazolin is typically the 
drug of choice due to its low cost, safety, duration of action, and activity against common 
SSI pathogens (staphylococci, streptococci, Enterobacteriaceae). (12) 
 
Despite the high prevalence of obesity, limited evidence exists on whether cefazolin dosing 
should be adjusted for obese patients. U.S. guidelines (2013) recommend 2 g IV for patients 
weighing 80–120 kg and 3 g IV for those over 120 kg. (12)  
 
This study aims to measure plasma and tissue concentrations of cefazolin administered per 
current recommendations and assess whether these levels are sufficient for effective 
prophylaxis. 
 

 
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1. CURRENT STATE OF KNOWLEDGE 
 
It is well established that preoperative antibiotic prophylaxis with cefazolin reduces the 
rate of surgical site infections (SSIs) in bariatric surgery. (13) However, evidence regarding 
the appropriate dose for obese or severely obese patients is scarce, of low quality, and 
contradictory. 
 
Unger et al., in a retrospective cohort study, suggest that obese patients can continue to 
receive a prophylactic dose of 2 g IV cefazolin, as they did not show a higher SSI rate 
compared to the non-obese population. (14) Peppard et al., in another retrospective cohort, 
found no significant difference in SSI rates between obese patients who received 2 g IV 
versus 3 g IV of cefazolin. (10) 
 
Ho et al. conducted a prospective cohort study examining plasma concentrations of 
cefazolin by administering 2 g IV to patients with BMI between 40–50 kg/m² and 3 g IV 
to those above 50 kg/m². (15) They concluded that a single prophylactic dose of 2 g IV 
cefazolin was sufficient regardless of obesity level. (15) Van Kralingen et al. analyzed 
plasma concentrations after a 2 g IV dose and reported that this exceeded the minimum 
inhibitory concentration (MIC) for Staphylococcus aureus. (16) Hites et al. studied plasma 
concentrations after a prophylactic 2 g IV dose and found no difference between patients 
weighing <120 kg and those >120 kg. (17) Plasma concentrations at 180 minutes were all 
above the target MIC. (17) 
 
Although these data are interesting, plasma concentration of the free fraction of cefazolin 
is only a limited pharmacokinetic marker. It is preferable to measure tissue concentration 
at the site of action. (18) 
 
Using a microdialysis technique, Brill et al. measured cefazolin concentration in the 
interstitial fluid of adipose tissue in obese versus non-obese patients. They showed that 
tissue distribution of cefazolin was lower in obese patients and decreased with increasing 
weight, suggesting a need for higher doses in this population. (18) 
 
However, more recently, Chen et al. analyzed a prospective cohort of patients undergoing 
gastric bypass or sleeve gastrectomy who received 2 g IV cefazolin, measuring plasma and 
tissue concentrations using High Performance Liquid Chromatography (HPLC). They 
concluded that the dose was adequate because tissue concentrations, although representing 
only 6–8% of plasma concentration, remained above the MIC for Staphylococcus aureus. 
(19) 
 
The wide variability in current medical literature is, in our opinion, partly due to the lack 
of a clear definition of MIC, which represents the threshold for effective antibiotic 
prophylaxis. 
In 
clean-contaminated 
surgery, 
staphylococci, 
streptococci, 
and 
Enterobacteriaceae are the main pathogens likely to cause SSIs. According to EUCAST, 
the MIC of cefazolin for methicillin-sensitive Staphylococcus aureus is 2 mg/L, while for 
Enterobacteriaceae it is 8 mg/L. Several authors consider that effective antibiotic 
prophylaxis requires plasma and/or tissue concentrations of cefazolin of 8 mg/L or higher. 
 

 
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It should be noted that the question of cefazolin prophylaxis has been more extensively 
studied in obese pregnant women undergoing cesarean section. These studies, although 
methodologically interesting and hypothesis-generating, are not addressed here due to their 
limited external validity for our bariatric surgery population. 
 
2. RESEARCH OBJECTIVES 
 
PRIMARY OBJECTIVE:  
The aim of this study is to determine whether the current cefazolin doses recommended by 
U.S. authorities for obese patients—2 g IV for those weighing <120 kg and 3 g IV for those 
≥120 kg—achieve plasma and tissue concentrations equal to or greater than 8 mg/L1. 
 
SECONDARY OBJECTIVES:  
We will also describe plasma and tissue concentrations of cefazolin by stratifying patients 
according to their weight: 
• 
<120 kg 
• 
≥120 kg and <150 kg 
• 
≥150 kg 
 
This stratification will allow us to identify whether any weight category is associated with 
insufficient plasma and/or tissue concentrations of cefazolin to provide effective antibiotic 
prophylaxis. 
 
3. STUDY DESIGN 
 
We will conduct a prospective analytical cohort study to examine plasma and tissue 
concentrations of cefazolin following administration of the standard doses recommended 
by U.S. practice guidelines. This will allow us to determine whether the current practice of 
surgical antibiotic prophylaxis with cefazolin is adequate. 
 
4. POPULATION AND SAMPLE 
 
TARGET POPULATION: All adults undergoing bariatric surgery at the Institut 
Universitaire de Cardiologie et de Pneumologie de Québec–Université Laval (IUCPQ-
UL). 
 
ACCESSIBLE POPULATION: All adults undergoing bariatric surgery of the sleeve 
gastrectomy type at IUCPQ-UL. 
 
SAMPLE: A subgroup of adults undergoing sleeve gastrectomy at IUCPQ-UL who have 
given preoperative consent to participate in the project (convenience sample). 
 
 
_____________________________ 
1 Minimum inhibitory concentration for Enterobacteriaceae according to EUCAST criteria. 
 
 

 
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CONTROL: A sample of 10 patients undergoing sleeve gastrectomy at IUCPQ-UL who 
have not been exposed to cefazolin (patients allergic to penicillin) will be recruited to form 
a control group for the purpose of validating the analysis method. 
 
PILOT SUBGROUP (BIOBANK): Ten subcutaneous adipose tissue biopsies from 
participants who have consented to the biobank will be obtained (8 from participants 
allergic to penicillin and 2 from participants exposed to cefazolin) to optimize cefazolin 
dosage measurement in this type of tissue. 
 
5. SAMPLING 
 
Patients will be invited to participate in the project during their preoperative consultation 
at the bariatric surgery clinic. All patients interested in participating will be included in the 
study if they do not meet any exclusion criteria (convenience sampling). 
 
6. SAMPLE SIZE AND INCLUSION/EXCLUSION CRITERIA 
 
SAMPLE SIZE:  
A total of 60 patients will be recruited for the study, with 20 patients in each weight 
category. Additionally, 10 patients allergic to penicillin will be recruited for the purpose of 
standardizing the HPLC analysis. 
 
INCLUSION CRITERIA:  
• Age ≥18  
• BMI ≥35 kg/m²  
• undergoing laparoscopic sleeve gastrectomy at IUCPQ-UL 
 
EXCLUSION CRITERIA: 
• Age <18  
• Weight >180 kg  
• Penicillin allergy (except control group)  
• Pregnancy or breastfeeding  
• Chronic kidney disease (eGFR <60 mL/min)  
• Liver cirrhosis  
• Intraoperative blood loss ≥1 L 
 
7. SUBJECT RECRUITMENT 
 
Subjects will be recruited during their preoperative consultation at the bariatric surgery 
clinic of IUCPQ-UL. A nurse from the bariatric surgery clinical research team will present 
the project to candidates who meet the inclusion criteria. The nurse will also have 
participants sign an informed consent form approved by the IUCPQ-UL Research Ethics 
Committee if they agree to participate. 
 

 
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8. MEASUREMENT INSTRUMENTS 
 
Plasma and tissue concentrations of cefazolin will be measured using high performance 
liquid chromatography (HPLC), a validated method widely used in similar studies. See the 
study procedure section for further details. 
 
9. STUDY PROCEDURE 
 
Each potential participant will be evaluated by a bariatric surgeon at IUCPQ-UL during 
their preoperative consultation. If the patient is eligible to participate in the study, they will 
meet with a research nurse on the same day. The nurse will explain the study procedure, 
answer any questions, and obtain informed consent if the patient wishes to participate. On 
this day, demographic data and routine preoperative blood tests will be collected. Renal 
and liver function data will be retrieved from the electronic medical record. To calibrate 
the HPLC technique, we will recruit 10 patients allergic to penicillin who will receive an 
alternative antibiotic prophylaxis for their sleeve gastrectomy. 
 
Each participant scheduled for laparoscopic sleeve gastrectomy will be admitted to 
IUCPQ-UL the day before surgery. They will meet their surgeon in their room, who will 
review preoperative tests and blood work, ensure the patient is fit for surgery, answer 
questions, obtain written consent for the surgery, and reconfirm participation in the 
research project. 
 
On the day of surgery, participants will receive an intravenous bolus of cefazolin at 
induction according to their weight: 
• 
Patients weighing less than 120 kg will receive 2 g IV. 
• 
Patients weighing 120 kg or more will receive 3 g IV. 
 
To standardize the timing between antibiotic administration and the first incision, 
prophylaxis will be administered by the anesthesiologist or respiratory therapist during 
patient skin preparation with chlorhexidine. 
 
Subcutaneous adipose tissue samples (~1 g) and skin samples (~0.6 cm²) will be collected 
(at the incision site) at incision (t = 0 min), 30 minutes after the start of the procedure, and 
at the end of surgery. Samples will be rapidly frozen at -80°C until extraction and analysis 
of cefazolin concentrations by HPLC. Blood samples (2 mL in K3 EDTA tubes) will also 
be collected at the same time points and kept on ice until centrifugation at 3,000 rpm for 
20 minutes. Plasma will then be recovered and frozen at -80°C until extraction and analysis 
by HPLC. 
 

 
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Cefazolin Extraction Procedure 
 
• 
Adipose Tissue: Samples will be prepared according to Waltrip et al. protocol (20): 
1. Precisely weighed the tissue; 
2. Add a cold extraction solution consisting of methanol/sodium acetate 1M 
(70/30, pH 5.2) in a 1:2 (w:v) ratio, containing a known amount of cefoxitin 
as an internal standard (21); 
3. Homogenize for 30 seconds; 
4. Cool for 10 min at -20°C; 
5. Centrifuge at 15,000 rpm for 10 min; 
6. Collect the supernatant and centrifuge again for 15 min at 15,000 rpm; 
7. Filter through 0.22 µm. 
 
• 
Dermis: Skin samples will be heated with a hair dryer for 20 seconds, and the 
epidermis will be separated from the dermis. (22) Dermis samples will then be 
weighed precisely and extracted using the same procedure as adipose tissue. 
 
• 
Plasma: 0.3 mL of plasma will be combined with an equal volume of 
methanol/sodium acetate 1M (70/30, pH 5.2) containing the internal standard, 
vortexed for 30 seconds, and incubated for 10 min at -20°C. Extracts will then be 
centrifuged for 10 min at 1,500 rpm, and supernatants will be collected and filtered 
through 0.22 µm. (20) 
 
Sample Analysis 
 
High-performance liquid chromatography will be performed at room temperature using a 
Shimadzu Prominence system (Columbia, MD, USA) consisting of an SIL-20ACHT 
autosampler, LC-20AT pump, and SPD-20A UV detector. The mobile phase will consist 
of 85% 0.01M sodium acetate (pH 5.2) and 15% of a solution composed of 96% acetonitrile 
and 4% methanol. (20) An Ultrasphere ODS 5 µm column (250 mm × 4.6 mm, Canadian 
Life Science, Peterborough, ON, Canada) and a µBondapak C18 pre-column (Waters, 
Mississauga, ON, Canada) will be used for separation at 1.5 mL/min of aliquots (20–100 
µL) of the injected extracts. Cefazolin and cefoxitin (internal standard) peaks will be 
detected by UV absorbance at 254 nm. EZ-Start software (Columbia, MD, USA) will be 
used for data acquisition, storage, and analysis. Ratios of cefazolin/cefoxitin peak heights 
will be converted to µg of cefazolin detected using a standard curve. 
 
10. DATA COLLECTION 
The results of tissue and blood concentration measurements will be stored on the secure 
servers of CRIUCPQ-UL. Once the target of 60 patients is reached, data collection will be 
carried out by two medical residents. These data will be entered electronically in an Excel 
file and subsequently retained for five years for potential future verification. 
 

 
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11. DATA ANALYSIS 
 
Descriptive statistical analyses will be performed to describe the baseline characteristics of 
our study population. 
 
In addition, for each time point analyzed, we will report: 
• 
the percentage of patients weighing <120 kg who do not reach the target tissue MIC 
• 
the percentage of patients weighing <120 kg who do not reach the target plasma 
MIC 
• 
the percentage of patients weighing ≥120 kg who do not reach the target tissue MIC 
• 
the percentage of patients weighing ≥120 kg who do not reach the target plasma 
MIC 
 
We will also determine the percentages of patients not reaching the tissue and plasma MIC 
for each weight category mentioned above. 
 
12. TIMELINE 
 
• June 2018: Project approval by the ethics committee 
• June 2018 to October 2018: Patient recruitment and data collection  
• September 2018: Application for research grant from the IUCPQ Foundation 
competition 
• November 2018: Data entry into Excel file and analysis 
• December 2018: Drafting of the scientific article 
• September 2019: IFSO Congress, Madrid 
• October 2019: IDWeek Conference 
 
13. STUDY LIMITATIONS 
 
The proposed study is exploratory in nature, meaning it is designed to verify the accuracy 
of current recommendations for preoperative antibiotic prophylaxis in surgery. We 
acknowledge that our study has limitations that may affect its external validity. First, it is 
a single-center study involving a sample of 60 patients undergoing sleeve gastrectomy—a 
relatively short procedure, mostly performed laparoscopically. Therefore, our results may 
not be generalizable to a broader population of patients undergoing clean-contaminated 
colorectal surgery. However, the relevance of our study remains undeniable, as current 
practice is based on very limited evidence and requires validation. 
 
14. ETHICS 
 
Participants will be approached by our research nurse during their preoperative 
consultation. For those interested, the purpose of the project, the participant’s involvement, 
and the benefits and risks of the study will be clearly explained at the time of signing the 
informed consent form. At all times, participants will be informed that they may withdraw 
their consent without fear that this will affect the quality of their care. 
 
Standard precautions will be taken to ensure patient confidentiality. 

 
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Research data will be stored on the secure server of CRIUCPQ-UL. 
 
15. EXPECTED IMPACT 
 
As previously stated, the study will generate data that we hope will validate or challenge 
current practices in preoperative antibiotic prophylaxis for morbidly obese patients. 
Depending on the results obtained, this study could highlight the need for a prospective 
cohort study to evaluate different dosing strategies based on weight. Furthermore, this 
study could generate hypotheses and encourage research into the appropriate dosing of 
other antimicrobial agents in the morbidly obese population. 
 
16. DISSEMINTION OF RESULTS  
 
The dissemination of these results will primarily take place through the writing of a 
scientific article. This article will then be published in a bariatric surgery or microbiology 
journal. It is also possible that these results will be presented at conferences in the two 
mentioned specialties, in front of colleagues from the medical field. 
 
 

 
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