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MODULE 7: PERIOPERATIVE PHARMACY
Section 1: Surgical Prophylaxis
Welcome to one of the most impactful and evidence-driven roles of the hospital pharmacist. In this section, you’ll master the science and strategy behind administering antibiotics before surgery to prevent infections, translating your meticulous verification skills into a critical, time-sensitive intervention.
PART 1.1
The “Why”: Preventing Surgical Site Infections (SSIs)
Understanding the Critical Goal of Pre-Incision Antibiotic Therapy
Surgical site infections (SSIs) are one of the most common and costly healthcare-associated infections. They are a significant cause of morbidity, leading to prolonged hospital stays, re-operations, and a substantial increase in healthcare costs. The fundamental principle of surgical prophylaxis is both simple and elegant: to have bactericidal concentrations of an appropriate antibiotic present in the patient’s tissues at the moment the surgical incision is made. This is not about treating an infection; it is about preventing one from ever starting. Your role as a pharmacist is to be the absolute authority on ensuring this single, critical dose is perfect.
Retail Pharmacist Analogy: The Preventative Maintenance Schedule
Think of a patient’s body as a high-performance car, and surgery is a major service that requires opening up the engine. You know that before the mechanic starts working, they need to ensure the garage is clean to prevent dust and grime from getting into the sensitive engine components. Surgical prophylaxis is this preventative cleaning, but on a microscopic level.
The pre-operative antibiotic is like a specialized cleaning spray that neutralizes any microscopic contaminants (bacteria) the moment the engine (the body) is opened.
- The 60-Minute Rule: You have to apply the cleaning spray just before the mechanic opens the hood. If you spray it too early, it will evaporate and be useless. If you spray it after the engine is already open, the contaminants are already inside. The timing is everything.
- Weight-Based Dosing: A small sports car needs less cleaning spray than a giant truck. Using the same amount for both would mean under-treating the truck, leaving it vulnerable. You must adjust the “dose” of the cleaner based on the size of the vehicle.
- Redosing: If the engine service is a very long one (a long surgery), the initial cleaning spray will wear off. You need to re-apply it at a scheduled interval to maintain the protective barrier throughout the entire service.
Your job is to be the master technician who ensures the right cleaning spray (antibiotic) is used, in the right amount (dose), at the exact right time, for the entire duration of the service (surgery).
The SCIP-Inf-1 Core Measure: Right Antibiotic, Right Time
The critical importance of this process is highlighted by its inclusion as a major national quality measure. The Surgical Care Improvement Project (SCIP) measure “Inf-1” specifically tracks whether a patient receives a prophylactic antibiotic within the correct time window before the surgical incision. Hospitals are publicly benchmarked on their compliance with this measure. The key principle is the “60-Minute Rule.”
Deep Dive: The 60-Minute Rule
To be effective, the antibiotic infusion must be started and completed within 60 minutes prior to the surgical incision. This ensures that the drug has had enough time to distribute from the bloodstream into the tissues, achieving peak bactericidal concentrations precisely when the surgeon makes the first cut.
- Special Case – Vancomycin & Fluoroquinolones: Because these medications require longer infusion times (typically 1-2 hours), the rule is modified. Their infusions should be started within 120 minutes prior to the incision to ensure the infusion is complete before the cut.
As a pharmacist, you are a guardian of this timeline. When verifying pre-op antibiotic orders, you must check the scheduled surgery time and ensure the administration time is appropriate. If you see an order for cefazolin to be given 3 hours before surgery, it is your duty to intervene and correct the timing.
PART 1.2
The Pharmacist’s Role: Pre-Op Verification and Dosing Guru
Applying your expertise in drug selection, allergy clarification, and dosing.
The perioperative pharmacist is the ultimate gatekeeper for surgical antibiotics. While surgeons and anesthesiologists are focused on the procedure, you are focused on the pharmacology. Your systematic verification process, a skill honed through years of final checks in the retail setting, is the most critical safety net. You are responsible for ensuring the right drug, for the right patient, at the right dose, and at the right time.
Matching the “Bug” to the “Drug”
The first step is to know what surgery is being performed. This tells you what tissues are being crossed and what the likely pathogens are. You will become intimately familiar with your hospital’s surgical prophylaxis guidelines, which are based on national standards from organizations like ASHP and IDSA.
| Surgical Procedure Type | Likely Pathogens | First-Line Prophylaxis | Alternative (True Beta-Lactam Allergy) |
|---|---|---|---|
| Cardiac / Orthopedic (with hardware) / Neurosurgery | S. aureus, S. epidermidis | Cefazolin | Vancomycin or Clindamycin |
| Colorectal | Enteric Gram-negatives, Anaerobes, Enterococci | Cefoxitin OR Cefazolin + Metronidazole | Clindamycin + (Gentamicin or Fluoroquinolone) |
| Hysterectomy (Vaginal or Abdominal) | Vaginal flora, Gram-negatives, Anaerobes | Cefazolin | Clindamycin or Vancomycin |
| Urologic (entering urinary tract) | Enteric Gram-negatives | Cefazolin or Ceftriaxone | Fluoroquinolone or Gentamicin |
Your role is to check the ordered antibiotic against the scheduled procedure and your hospital’s guideline. If a surgeon orders cefazolin for a colorectal case, you must intervene and recommend the addition of metronidazole to provide adequate anaerobic coverage.
The Beta-Lactam Allergy Deep Dive
This is one of the most important and impactful interventions a perioperative pharmacist can make. More than 90% of patients with a listed penicillin allergy are not truly allergic and can safely receive cephalosporins. Inappropriately avoiding cefazolin leads to the use of second-line agents like vancomycin and clindamycin, which are less effective, have more side effects, and contribute to antibiotic resistance. Your job is to be an “allergy detective.”
Your Role in Challenging Assumptions
When you see a “penicillin allergy” listed, you must investigate. Your skills in patient counseling are key. You or the pre-op nurse must ask the patient the right questions:
- What was your reaction? A simple rash or GI upset is not a true allergy and does not preclude the use of a cephalosporin. Anaphylaxis, hives, or swelling of the lips/throat is a true IgE-mediated allergy.
- When did this happen? An allergy from childhood is much less likely to still be present than one from last year.
The risk of cross-reactivity between penicillins and cephalosporins is NOT based on the shared beta-lactam ring, but on the similarity of their R1 side chains. Cefazolin has a completely different side chain from ampicillin and penicillin. The true cross-reactivity risk between penicillin and cefazolin in a patient with a non-anaphylactic allergy is less than 1%. Armed with this knowledge, you can confidently recommend the use of cefazolin in the vast majority of patients with a listed penicillin allergy.
Weight-Based Dosing: A Masterclass
The principle of “one size fits all” is dangerous in surgical prophylaxis, especially with the rising prevalence of obesity. Underdosing an obese patient means that the antibiotic concentration in the tissue may never reach a bactericidal level, rendering the prophylaxis useless. Your expertise in pharmacokinetics and dose calculations is essential to prevent this failure.
Cefazolin: The Workhorse
Cefazolin is the most common antibiotic for surgical prophylaxis. Modern guidelines recommend weight-based dosing, and it is your job to ensure this is followed.
The Dangers of Underdosing Cefazolin in Obesity
Giving a 2g dose of cefazolin to a 150 kg patient is a setup for failure. Studies have shown that tissue concentrations in these patients can fall below the MIC for S. aureus before the surgery is even finished. You must be the advocate for appropriate, evidence-based dosing.
| Patient Weight | Recommended Cefazolin Dose |
|---|---|
| < 120 kg | 2 grams |
| ≥ 120 kg | 3 grams |
Your first action when verifying a pre-op cefazolin order is to check the patient’s weight. If you see a 130 kg patient with an order for 2g of cefazolin, you must intervene and recommend increasing the dose to 3g.
Vancomycin & Gentamicin
- Vancomycin: The dose for surgical prophylaxis is 15 mg/kg based on ACTUAL body weight, rounded to the nearest 250 mg. A 1g flat dose is no longer acceptable. A 130 kg patient requires a 2g dose (130 kg * 15 mg/kg = 1950 mg).
- Gentamicin: Often used in combination for GU or colorectal surgery. Prophylactic dosing is typically 5 mg/kg based on ADJUSTED body weight for obese patients to avoid toxicity.
PART 1.3
Intraoperative Redosing: Beating the Clock
Maintaining Coverage During Long Surgical Procedures
The goal of prophylaxis is to maintain adequate tissue concentrations for the entire duration of the surgery. For long surgical procedures, a single pre-operative dose is not enough. The antibiotic will be metabolized and cleared, and its concentration will drop below the MIC. Therefore, intraoperative redosing is required. Your role is to understand the timing and communicate it effectively to the anesthesia and surgical teams.
The “Two Half-Lives” Rule of Thumb
The general principle for redosing is to give another dose after approximately two half-lives of the drug have passed. This ensures that the concentration never dips into the sub-therapeutic range. The redosing interval is always timed from the administration of the pre-operative dose, not from the incision time.
| Antibiotic | Typical Half-Life | Standard Redosing Interval (from pre-op dose) |
|---|---|---|
| Cefazolin | ~2 hours | Every 4 hours |
| Cefoxitin | ~1 hour | Every 2 hours |
| Clindamycin | ~3 hours | Every 6 hours |
Factors that Accelerate Clearance: In cases of major blood loss (e.g., > 1500 mL), a redose should be given as soon as the patient is stabilized, as a significant portion of the antibiotic has been lost.
Clinical Pearl: Redosing Vancomycin is Rarely Necessary
You will notice vancomycin is missing from the redosing table. This is intentional. Vancomycin has a long half-life (6-8 hours or more). For the vast majority of surgical procedures, a single, appropriately weight-based pre-operative dose is sufficient to maintain adequate tissue concentrations for the entire case. Intraoperative redosing of vancomycin is generally not recommended unless the procedure is exceptionally long (> 8 hours) or there is massive, un-resuscitated blood loss. This is a key piece of knowledge that allows you to prevent unnecessary doses of a nephrotoxic drug.
