Diabetic Foot Infection

A diagnosis of diabetic foot infection MUST be made using clinical signs and symptoms, not just microbiological results. All open wounds will be colonised with organisms, making the positive culture difficult to interpret.
Key recommendations:

  • Only use antibiotics if clinical signs of infection
  • Send microbiological samples early in infection – tissue aspirates are preferable to wound swabs
  • Continue therapy until the infection has resolved, not until the wound has healed
  • Treatment plan should include wound care, pressure relief and early vascular assessment, with referral to vascular surgeons if impalpable foot pulses – see Wound formulary
  • Osteomyelitis
    • suspect if able to touch bone through the wound with a sterile probe
    • suspect in a non-healing diabetic ulcer with adequate blood supply
    • refer to Combined Diabetic Foot Clinic
    • deep swab or tissue samples are essential for diagnosis.  Delay therapy pending microbiology results in chronic cases
    • treat for 6 weeks minimum.
  • Typical pathogens (antibiotic-naïve = no systemic antimicrobials in last 3 months)
    • antibiotic-naïve: Staph aureus and beta-haemolytic streptococci
    • not antibiotic-naïve or chronic: as above plus Gram-negative bacilli, enterococci, anaerobes.
  • Discuss treatment options with Microbiology if organisms isolated are not covered by empiric guidance for severity of infection.
  • All doses are for adults with normal renal function or mild renal impairment.

Clinical manifestation of a diabetic foot infection

Infection severity

PEDIS grade

Wound lacking purulence or any manifestations of inflammation

Uninfected

1

Presence of ≥2 manifestations of inflammation (purulence, or erythema, pain, tenderness, warmth or induration), but any cellulitis/ erythema extends ≤2 cm around the ulcer, and infection is limited to the skin or superficial subcutaneous tissues; no other local complications or systemic illness.

Mild

2

Infection (as above) in a patient who is systemically well and metabolically stable but which has 1 of the following characteristics: cellulitis extending >2cm, lymphangitic streaking, spread beneath the superficial fascia, deep-tissue abscess, gangrene and involvement of muscle, tendon, joint or bone.

Moderate

3

Infection in a patient with systemic toxicity or metabolic instability (e.g. fever, chills, tachycardia, hypotension, confusion, vomiting, leukocytosis, acidosis, severe hyperglycaemia or azotaemia).

Severe

4

Table taken from: IDSA grading of severity of diabetic foot infection - see Lipsky, B. A. et al., 2004.  Diagnosis and Treatment of Diabetic Foot Infections.  Clinical Infectious Diseases, 39, pp. 885-910
NOTE: Definitions of terms can be found in footnotes to table 4 of the above reference. 
Foot ischaemia may increase the severity of any infection, and the presence of critical ischaemia often makes the infection severe. PEDIS: perfusion, extent/size, depth/tissue loss, infection, and sensation.

For glossary of terms see Glossary

IDSA - mild
Antibiotic-naïve:(no systemic agents in the last 3 months)

Oral/IV flucloxacillin * 1g 4 times daily

7 days (including IV to oral switch)

ISDA - mild
If not antibiotic-naïve or in penicillin allergy or MRSA known carrier or proven infection

Oral doxycycline 100mg twice daily

7 days (including IV to oral switch)

IDSA - Moderate
Antibiotic-naïve: Consider admission and bed rest. If patient remains as out-patient, ensure early clinic review.  

Oral flucloxacillin 1g or IV flucloxacillin 2g 4 times daily
AND Oral metronidazole * 400mg 3 times daily

7 days (including IV to oral switch)

IDSA - Moderate
If not antibiotic-naïve or in penicillin allergy

Oral clindamycin 600mg 3 times daily
OR IV clindamycin 600mg 4 times daily

7 days (including IV to oral switch)

IDSA - Moderate
MRSA known carrier or proven infection

IV vancomycin * - refer to hospital vancomycin dosing guidelines

7 days (including IV to oral switch)

IDSA - Severe
Antibiotic-naïve

IV flucloxacillin * 2g every 6 hours
PLUS IV clindamycin * - 600mg every 6 hours
AND/OR IV aztreonam * - 2g 3 times daily
AND/OR Oral metronidazole * - 400mg 3 times daily
OR IV metronidazole * - 500mg 3 times daily

7 to 10 days. Staph aureus bacteraemia (SAB) requires 14 days of IV therapy. Review need for Gram-negative cover and rationalise therapy depending on microbiology results.

IDSA - Severe
If not antibiotic-naïve

IV piperacillin/tazobactam * 4·5g 3 times daily
AND IV clindamycin 600mg 4 times daily

7 to 10 days. Staph aureus bacteraemia (SAB) requires 14 days of IV therapy. Review need for Gram-negative cover and rationalise therapy depending on microbiology results.

IDSA - Severe
In penicillin allergy or MRSA known carrier or proven infection

IV vancomycin* Follow hospital vancomycin guidelines. Aim for trough 15 to 20mg/L.
AND IV clindamycin 600mg 4 times daily
AND/OR IV aztreonam * - 2g 3 times daily
AND/OR Oral metronidazole * - 400mg 3 times daily
OR IV metronidazole * - 500mg 3 times daily

7 to 10 days. Staph aureus bacteraemia (SAB) requires 14 days of IV therapy. Review need for Gram-negative cover and rationalise therapy depending on microbiology results.

Osteomyelitis
Acute (IDSA/PEDIS Grade 4)

IV flucloxacillin * 2g every 6 hours
AND IV clindamycin - 600mg every 6 hours
AND/OR 
IV aztreonam * - 2g 3 times daily

6 to 12 weeks with at least 2 weeks of IV therapy in acute setting

Review need for Gram-negative cover and rationalise therapy depending on microbiology results.

* Dose to be adjusted in moderate or severe renal impairment or in renal replacement therapy.

Osteomyelitis
If not antibiotic-naïve or in penicillin allergy:

IV vancomycin * - follow hospital vancomycin guidelines. Aim for trough 15 to 20mg/L.
AND IV clindamycin - 600mg 4 times daily
AND IV aztreonam * - 2g 3 times daily

6 to 12 weeks with at least 2 weeks of IV therapy in acute setting

Review need for Gram-negative cover and rationalise therapy depending on microbiology results.

* Dose to be adjusted in moderate or severe renal impairment or in renal replacement therapy.

Osteomyelitis
If MRSA known carrier or proven infection: Consider additional gram-negative and anaerobic cover.

ADD IV vancomycin* - follow hospital vancomycin guidelines. Aim for trough 15 to 20mg/L.
AND Rifampicin 450mg twice daily
OR Sodium fusidate 500mg 3 times daily

6 to 12 weeks with at least 2 weeks of IV therapy in acute setting

Review need for Gram-negative cover and rationalise therapy depending on microbiology results.

* Dose to be adjusted in moderate or severe renal impairment or in renal replacement therapy.

Osteomyelitis
Non-acute (IDSA/PEDIS Grade 2-3)

Clindamycin 600mg 3 times daily
AND Ciprofloxacin * 750mg twice daily

6 to 12 weeks with at least 2 weeks of IV therapy in acute setting

Review need for Gram-negative cover and rationalise therapy depending on microbiology results.

* Dose to be adjusted in moderate or severe renal impairment or in renal replacement therapy.

Editorial Information

Last reviewed: 30 September 2018

Next review: 30 September 2021

Author(s): Antimicrobial Management Team

Approved By: TAM Subgroup of ADTC

Reviewer Name(s): Area Antimicrobial Pharmacist

Document Id: AMT166