Red Flags
- Pain out of proportion to examination, woody induration, crepitus, skin necrosis, or systemic toxicity — necrotising fasciitis until proven otherwise; emergency surgical consult[1]
- Sepsis criteria with rapidly spreading erythema and bullae — severe non-purulent SSTI; broad-spectrum IV antibiotics within 1 hour, surgical exploration if necrotising[1]
- Diabetic foot infection with loss of protective sensation, deep ulcer, or osteomyelitis features (probe-to-bone) — admit, broad-spectrum cover, surgical consult[1]
- Animal or human bite to hand, face, or over a joint — infection rate >20%; prophylactic amoxicillin-clavulanate, tetanus, rabies risk assessment[1]
First-line treatment
Interventions
- Incision and drainage (I&D)[1]Definitive treatment for simple cutaneous abscesses; antibiotics often unnecessary after adequate drainage in immunocompetent patients with single small abscess
- Urgent surgical exploration[1]Necrotising fasciitis or gas gangrene — immediate aggressive debridement of all necrotic tissue, broad-spectrum antibiotics (e.g. piperacillin-tazobactam + vancomycin + clindamycin for toxin suppression). Mortality climbs steeply with each hour of surgical delay
First-line drug therapy
| Drug | Class | Adult | Paediatric | Notes |
|---|---|---|---|---|
| Cephalexin[1] | First-generation cephalosporin | 500 mg PO QID for 5–7 days | 25–50 mg/kg/day divided QID | Mild non-purulent cellulitis (streptococci-dominant). Switch to MRSA cover if no improvement at 48–72 h |
| Dicloxacillin or flucloxacillin[1] | Antistaphylococcal penicillin | 500 mg PO QID for 5–7 days | 25–50 mg/kg/day divided QID | Equivalent first-line for non-MRSA cellulitis where available |
| Doxycycline or trimethoprim-sulfamethoxazole[1] | Oral MRSA-active agent | Doxycycline 100 mg PO BD; TMP-SMX 1–2 DS tablets PO BD for 5–7 days | TMP-SMX 8–12 mg/kg/day divided BD (TMP component) | Mild-to-moderate purulent SSTI requiring antibiotics; covers community-acquired MRSA |
| Vancomycin[1] | Glycopeptide (IV) | 15–20 mg/kg IV q8–12h, target trough 15–20 mg/L | 10–15 mg/kg IV q6h | Severe purulent SSTI, suspected/confirmed MRSA, or severe non-purulent cellulitis with systemic toxicity |
| Piperacillin-tazobactam[1] | Broad-spectrum antipseudomonal beta-lactam-inhibitor combination | 4.5 g IV q8h (extended infusion preferred where available) | 300 mg/kg/day divided q6h (max 16 g/day) | Severe SSTI with diabetic foot or polymicrobial concern; combine with vancomycin or linezolid for MRSA cover until cultures return |
Cephalexin[1]
First-generation cephalosporin
- Adult
- 500 mg PO QID for 5–7 days
- Paediatric
- 25–50 mg/kg/day divided QID
Mild non-purulent cellulitis (streptococci-dominant). Switch to MRSA cover if no improvement at 48–72 h
Dicloxacillin or flucloxacillin[1]
Antistaphylococcal penicillin
- Adult
- 500 mg PO QID for 5–7 days
- Paediatric
- 25–50 mg/kg/day divided QID
Equivalent first-line for non-MRSA cellulitis where available
Doxycycline or trimethoprim-sulfamethoxazole[1]
Oral MRSA-active agent
- Adult
- Doxycycline 100 mg PO BD; TMP-SMX 1–2 DS tablets PO BD for 5–7 days
- Paediatric
- TMP-SMX 8–12 mg/kg/day divided BD (TMP component)
Mild-to-moderate purulent SSTI requiring antibiotics; covers community-acquired MRSA
Vancomycin[1]
Glycopeptide (IV)
- Adult
- 15–20 mg/kg IV q8–12h, target trough 15–20 mg/L
- Paediatric
- 10–15 mg/kg IV q6h
Severe purulent SSTI, suspected/confirmed MRSA, or severe non-purulent cellulitis with systemic toxicity
Piperacillin-tazobactam[1]
Broad-spectrum antipseudomonal beta-lactam-inhibitor combination
- Adult
- 4.5 g IV q8h (extended infusion preferred where available)
- Paediatric
- 300 mg/kg/day divided q6h (max 16 g/day)
Severe SSTI with diabetic foot or polymicrobial concern; combine with vancomycin or linezolid for MRSA cover until cultures return
Safety-net
- Mark the edge of the redness with a pen; if it spreads beyond the line in 24 hours, return same-day[1]
- Severe pain that seems out of proportion to the visible skin redness, blackening, or fluid-filled blisters — call emergency services. This may be a flesh-eating infection[1]
- Fever >38°C, rigors, or feeling unwell with a skin infection — same-day medical review; oral antibiotics may not be enough[1]
Referral criteria
- Suspected necrotising fasciitis (pain out of proportion, crepitus, skin necrosis, rapid progression)Emergency department; immediate surgical exploration[1]
- Sepsis with SSTIEmergency department; IV antibiotics within 1 hour[1]
- Diabetic foot infection with deep involvement, ischemia, or systemic featuresMultidisciplinary diabetic foot service; surgical and vascular review[1]
- Recurrent SSTI (≥3 episodes in 1 year)Infectious diseases for decolonisation strategy and screening for predisposing factors[1]
Clinical summary
Diagnostic stratification and antimicrobial management of purulent and non-purulent SSTIs by severity, including consideration for necrotising infections.