Educational draft · awaiting clinical reviewUse Rapid for revision, not patient-care decisions. Check current national and local guidance and the BNF or BNFC before acting.
2 min synopsisUK scopeSources checked 13 Sept 2026Clinical review pending
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Sepsis or threatened limb
Severe infection, necrotising infection, deep abscess, compartment infection, gangrene or infection with significant ischaemia may progress rapidly despite limited pain or inflammation.
Action: Refer immediately to acute services, alert the multidisciplinary foot service, obtain urgent surgical and vascular review, take cultures without delaying antibiotics, and begin sepsis resuscitation when indicated.
Synopsis
Distinguish colonisation from clinical infection, grade mild, moderate and severe disease, and link severity to sampling, antibiotics, admission and source control.
Severe diabetic foot infection means local infection with systemic manifestations; manage urgently in acute services with sepsis care, parenteral therapy when needed and early surgical assessment.
Infection with gangrene, deep abscess, necrotising features or significant ischaemia threatens the limb even if observations are normal; obtain urgent surgical and vascular input.
Diagnose infection clinically when at least two inflammatory findings are present, including swelling, erythema, tenderness, warmth or purulent discharge, after excluding mimics; culture alone shows colonisation.
Key red flags
Fever, tachycardia, tachypnoea, hypotension, confusion, rigors or metabolic deterioration indicates systemic illness and may meet severe infection criteria.
Crepitus, bullae, skin anaesthesia, dusky necrosis, severe pain out of proportion or rapid spread raises concern for necrotising soft-tissue infection.
Fluctuance, purulent tracking, deep tenderness, exposed joint or bone, or gas on imaging suggests an abscess or deep compartment infection requiring source control.
A cool foot, gangrene, absent Doppler signals or severe perfusion deficit accompanying infection requires urgent vascular and surgical coordination.
Severe infection
Severe infection is local infection with at least two SIRS findings: temperature >38°C or <36°C; heart rate >90/min; respiratory rate >20/min or PaCO2 <4.3 kPa (32 mmHg); white count >12,000/mm³, <4,000/mm³ or >10% bands. Hypotension, confusion or organ dysfunction signals even greater danger.
Investigation priorities
01
Deep tissue or bone microbiologyFirst step
Identify likely pathogens and enable de-escalation after the clinical diagnosis of infection is made.
Management branches
Acute treatmentFrom severity to immediate action
Clinical infection is present, after rapidly excluding sepsis, necrotising disease, abscess, gangrene and critical ischaemia.
For severe or limb-threatening features, refer immediately, obtain urgent surgical and vascular assessment, take blood and deep cultures where indicated, and start sepsis management and intravenous antibiotics without harmful delay.
For mild or stable moderate infection, obtain a debrided tissue specimen before or close to antibiotics, choose oral therapy when absorption and severity allow, and define a review point and stop duration.
Preferred branchDeep or complicated infection
Deep abscess, compartment involvement, necrosis, gangrene, exposed structures, osteomyelitis or infection with PAD is suspected.
Key medicines
FlucloxacillinFor mild infection, 500 mg orally four times daily for 7 days; extend by up to 7 further days only after clinical review of response.Confirm no immediate or severe penicillin allergy and avoid after flucloxacillin-associated jaundice or hepatic dysfunction. Usual renal function needs no reduction; at creatinine clearance <10 mL/min the SmPC requires dose reduction or interval extension, caps adults at 1 g every 8–12 hours, and gives no dialysis supplement, so use a named renal-antimicrobial or pharmacist schedule. Stop or change for hypersensitivity, hepatic injury, resistance or deterioration.
ClarithromycinFor mild infection with penicillin allergy or intolerance, 500 mg orally twice daily for 7 days; extend by up to 7 days only after reassessment.Check macrolide allergy, QT prolongation, hepatic disease and CYP3A interactions including simvastatin or lovastatin. At creatinine clearance <30 mL/min halve this 500 mg twice-daily regimen to 250 mg twice daily and do not continue beyond 14 days; severe hepatic failure with renal impairment is contraindicated. Avoid routine use in pregnancy when erythromycin is the NICE-listed alternative; narrow or stop by response and cultures.
National guidance is shown before implementation-dependent detail. Typical adult dose examples remain subject to patient factors, contraindications and the live BNF or specialist protocol. Source check completed 13 Sept 2026; clinical approval remains outstanding.
Flucloxacillin 500 mg capsules SmPCSections 4.2–4.6; renal threshold, maximum interval, dialysis, allergy and hepatic cautions; text revised 1 July 2026.
Clarithromycin 500 mg tablets SmPCSections 4.2–4.6; renal dose reduction, 14-day renal limit, QT, hepatic and interaction cautions; text revised 1 July 2026.