The choice of antimicrobial is ultimately influenced by the surgical procedure and associated risk factors. It should provide coverage of the expected microbiological flora at the incision site.14 This is further influenced by multiple patient-specific risk factors including:
- pre-existing infection
- recent antimicrobial use
- known colonisation with a resistant organism
- prolonged hospitalisation
- renal function
- allergy status
For the majority of procedures, a first-generation cephalosporin, such as cefazolin, remains the preferred antimicrobial for prophylaxis.3,14,18 Uptake of this recommendation was shown across current Australian practice in the 2016 Surgical National Antimicrobial Prescribing Survey, with cefazolin being the most commonly prescribed antimicrobial for procedural (69%) and post-procedural prophylaxis (57%). However, 50% of the post-procedural cefazolin prescribing was deemed inappropriate.7
When indicated, a single defined dose of antibiotic(s), for example, 2 g intravenous cefazolin, is sufficient for most procedures.3,14 This dose may be influenced by patient-related risk factors such as age, renal function and weight.15-17
Right route of administration
Parenteral administration (intravenous or intramuscular) is the preferred route for surgical antimicrobial prophylaxis. However, there are exceptions, including intracameral use for ophthalmic procedures,3,19 oral antibiotics for transurethral resections of the prostate3 and surgical terminations of pregnancy,3,20 and oral amoxicillin before certain dental procedures for endocarditis prophylaxis.3,12,21
Within the acute setting, the 2016 Surgical National Antimicrobial Prescribing Survey identified intravenous administration as the most common route for procedural (94.2%) and post-procedural antimicrobials (64.5%). Oral administration accounted for 20.4% of post-procedural antimicrobials, however only 18.4% of oral administrations were deemed appropriate.7
Overall, there are conflicting data regarding the benefits of topical antimicrobial prophylaxis,22 and it is currently not indicated for most wounds, especially those resulting from clean procedures. The most recently updated Centers for Disease Control and Prevention guidelines for the prevention of surgical site infections also advise against the application of topical prophylaxis.8 Despite insufficient evidence, antibiotic ointments and creams are frequently used for topical prophylaxis.23
Antimicrobial prophylaxis should not be used as a stopgap for inadequate infection prevention measures. Similarly, topical prophylaxis should not be a substitute for good surgical closure technique and dressing management, particularly in cases where wounds are hard to seal and dress.
The most recent Cochrane review proposes that topical prophylaxis ‘probably’ prevents surgical site infections when compared to antiseptics or no topical antibiotic use.24 However, when comparing topical antibiotics to no topical antibiotic use, the number needed to treat for one additional beneficial outcome was 50. It is important to note that this Cochrane review of trials from 1967 to 2014 found a considerably high risk of bias. The authors could not draw conclusions regarding the influence of topical antibiotics on antibiotic resistance and wound healing.
An earlier review on topical prophylaxis in dermatological procedures concluded that there was no significant difference between topical antimicrobials and petrolatum or paraffin for postsurgical wound infections.25 An Australian study found that topical chloramphenicol for high-risk suture wounds produced only a moderate absolute reduction in infection rate that was statistically but not clinically significant.26 An earlier Australian randomised controlled trial including 1801 surgical wounds found no significant benefit from mupirocin or paraffin ointments before occlusive dressings when compared to no ointment use.27
High use of topical prophylaxis may increase the risk of antimicrobial resistance. A New Zealand study has correlated increasing use of topical fusidic acid with a rapid clonal expansion of fusidic acid-resistant Staphylococcus aureus.28
Topical mupirocin is commonly indicated for decolonisation of methicillin-susceptible S. aureus (MSSA) and methicillin-resistant S. aureus (MRSA). Increased use has been associated with ‘emergence of resistance through enhanced selective pressure and cross-transmission’.29 A Korean drug utilisation review found an increase in mupirocin consumption correlated with increases of low- and high-level mupirocin resistance in MRSA infections.30
Unrestricted use of mupirocin, in particular for wounds and pressure sores, is strongly associated with increased resistance.29 Fortunately, in Australia, mupirocin is a Schedule 4 prescription-only medicine so both GPs and hospital prescribers have a significant role in reducing its inappropriate use.
Right timing of administration
Appropriate surgical prophylaxis achieves antimicrobial serum and tissue concentrations that exceed the minimum inhibitory concentration for the most probable organisms at the surgical site during the procedure.14 Appropriate timing of antimicrobial administration is crucial to prevent effective surgical site infection.
Incorrect timing of prophylaxis before or during a procedure was the most common factor in inappropriate prescribing in the 2016 Surgical National Antimicrobial Prescribing Survey (45.7%).7
Most guidelines, including Therapeutic Guidelines: Antibiotic, recommend that preoperative intravenous antibiotics be given within 60 minutes of incision.3,8,14,31-34 More recently, the World Health Organization recommended administration within 120 minutes of incision.35 For caesarean sections, evidence supports antimicrobial prophylaxis before cord clamping rather than afterwards.36,37
A single preoperative dose is adequate for the majority of procedures. Post-procedural doses of intravenous antibiotics (up to 24 hours) are only required in defined circumstances, such as some cardiac and vascular surgeries, and lower limb amputation.38-40
The 2016 Surgical National Antimicrobial Prescribing Survey found that incorrect duration was the most common factor in inappropriate post-procedural antimicrobial prescribing (73.7%).7 Prophylaxis should not extend beyond 24 hours, regardless of the surgical procedure. Intravenous and oral antibiotic prophylaxis offer no benefit beyond this period.3
Post-procedural antimicrobials may be initiated in the acute setting but can be reviewed and re-assessed during follow-up with the GP. It is essential that the surgical team clearly communicates with the GP about post-procedural antimicrobial use (usually in the discharge summary).
A recent retrospective cohort study included 1488 patients who received at least 24 hours of parenteral or oral antibiotic therapy. The study identified 20% (n=298) of these patients experienced at least one antibiotic-associated adverse event, and 20% (n=56) of those adverse events were associated with non-clinically indicated antibiotic regimens.41 The authors stated for every 10 additional days of antibiotic therapy, there was a 3% increased risk of adverse events.41