Good practice recommendations for re-dosing antibiotics for surgical prophylaxis in adults

Re-dosing antibiotics for surgical prophylaxis to maintain antibiotic concentrations during prolonged surgical procedures can significantly reduce the rate of surgical site infections.¹ Guidance on when to re-dose varies, NICE Guideline 125² states to give a repeat dose of antibiotic prophylaxis when the operation is longer than the half-life of the antibiotic given; United States guidance advises re-dosing after two half-lives³.  These SAPG good practice recommendations are based on current good practice in NHS boards in Scotland, published evidence, and information on antibiotic half-lives.

The following should be taken into account when using this guidance:

• For procedures lasting more than 4 hours, re-dosing (where indicated) after 4 or 8 hours promotes safe and effective surgical prophylaxis.
• This guidance does not cover surgery lasting for longer than 10 hours.
• Decisions around re-dosing should be made on an individual patient basis taking account of the risks and benefits of repeat dosing.
• These recommendations on re-dosing are for patients with normal renal and hepatic function unless otherwise stated.
• Patients with complex management requirements should be discussed with microbiology in advance.
• These recommendations include re-dosing advice where there is intraoperative blood loss of 1500mL or more.^4,5 It is not recommended to give a repeat dose of antibiotics after every subsequent 1500mL blood loss and specialist advice is needed where blood loss exceeds 3000mL.

Additional information about amoxicillin and co-amoxiclav:
The American Society of Health-System Pharmacists, Infectious Diseases Society of America, Surgical Infection Society, and Society for Healthcare Epidemiology of America recommend re-dosing ampicillin after 2 hours (note: amoxicillin and ampicillin have similar pharmacokinetic profiles)³ Consider re-dosing interval reflecting on local current practice and postoperative infection rates.

Additional information about gentamicin:
Literature suggests re-dosing of gentamicin is not required when a single dose of 5 mg/kg is used. A lower dose or alternative antibiotic is recommended in patients with reduced renal function (Creatinine Clearance [CrCl] less than 20mL/min). A pharmacokinetic evaluation of gentamicin dosing regimens in abdominal surgery found 3 mg/kg was comparable to 5 mg/kg at 6 hours from prophylactic dose.⁴ However, longer surgeries, eg over 8 hours, may require re-dosing in patients with normal renal function. Consider re-dosing with 2.5 mg/kg after 6 hours following a 5mg/kg dose in patients with CrCl over 50mL/min undergoing colorectal surgery.⁶ Renal toxicity has been observed in patients receiving flucloxacillin and gentamicin for surgical prophylaxis in orthopaedic surgery; therefore, in these instances consider lower doses or alternative antibiotics. As an alternative to gentamicin, consider co-amoxiclav, or if penicillin allergy, ciprofloxacin.

References

Reviewed by: Association of Scottish Antimicrobial Pharmacists (ASAP) 

Scottish Antimicrobial Prescribing Group (SAPG) | August 2025 for review August 2028
Content updated: October 2025