Skin & Soft Tissue Infections (SSTI)

Choice of Antimicrobials

Indication for Therapy	Usual Causative Organisms	Antimicrobial Regimens
Purulent SSTI (ie. skin abscesses, carbuncles and furuncles)	Staphylococcus aureus	Antimicrobials not routinely recommended for management of uncomplicated purulent SSTIs Incision and drainage most effective management Recurrent infection (x5-7 days of): co-trimoxazole 1 DS (trimethoprim [TMP] 160 mg/sulfamethoxazole [SMX] 800 mg) PO q12h OR doxycycline 100mg PO q12h
Non-purulent SSTI Uncomplicated cellulitis, impetigo, erysipelas OR Superficial ulcers with cellulitis in non-diabetic patients	Group A, C, and G , Streptococcus Staphylococcus aureus	cephalexin 500 mg PO q6h x 5-7 days
		ceFAZolin 1 g IV q8h^† x 5-7 days
		β-lactam allergy (anaphylaxis): moxifloxacin 400 mg PO q24h OR clindamycin 300 mg PO q6h or 600 mg IV q8h
	Methicillin-resistant Staphylococcus aureus (MRSA) suspected	co-trimoxazole 1 DS (trimethoprim [TMP] 160 mg/sulfamethoxazole [SMX] 800 mg) PO q12h + cephalexin 500 mg PO q6h
		doxycycline 100 mg PO q12h + cephalexin 500 mg PO q6h
		vancomycin (dosing as per hospital guidelines)
Necrotizing fasciitis^* Note: If MRSA suspected, add vancomycin	Invasive Group A Streptococcus	penicillin G 4 MU IV q4h + clindamycin 900 mg IV q8h +/- IVIG 1 g/kg x 1, then 0.5 g/kg at days 2 and 3 (if signs of streptococcal toxic shock syndrome) + Consider ID consult
	Invasive Group A Streptococcus	β-lactam allergy (anaphylaxis): vancomycin (dose as per hospital guidelines) + clindamycin 900 mg IV q8h +/- IVIG 1 g/kg x 1, then 0.5 g/kg on days 2 and 3 (if signs of streptococcal Toxic Shock Syndrome) + Consider ID consult
	Mixed aerobic Gram-negative bacilli and anaerobes	piperacillin/tazobactam 3.375 g IV q6h
	Mixed aerobic Gram-negative bacilli and anaerobes	cefTRIAXone 1-2 g IV q24h + metroNIDAZOLE 500 mg IV q12h
Diabetic foot infection OR Decubitus ulcer (infected) Note: If MRSA suspected, add vancomycin	Most mild superficial infections are S. aureus and Streptococcus spp. More complicated infections may include S. aureus, Streptococcus spp., Enterobacterales, and anaerobes	Mild infection: superficial, localized with no systemic involvement
		cephalexin 500 mg PO q6h
		amoxicillin/clavulanic acid 875 mg/125 mg PO q12h
		co-trimoxazole 1 DS (trimethoprim [TMP] 160 mg/sulfamethoxazole [SMX] 800 mg) PO q12h + metroNIDAZOLE 500 mg PO q12h
		ceFAZolin 1 g IV q8h^†
		Moderate infection: full thickness ulcer with deep tissue involvement; NO systemic illness
		cefTRIAXone 1 g IV q24h + metroNIDAZOLE 500 mg PO/IV q12h
		amoxicillin/clavulanic acid 875 mg/125 mg PO q12h
		metroNIDAZOLE 500 mg PO/IV q12h + moxifloxacin 400 mg PO q24h
		Severe infection: systemic or bone involvement^*
		piperacillin/tazobactam 3.375 g IV q6h
		cefTRIAXone 1 g IV q24h + metroNIDAZOLE 500 mg PO/IV q12h
		β-lactam allergy (anaphylaxis): metroNIDAZOLE 500 mg PO/IV q12h + moxifloxacin 400 mg PO q24h
Cellulitis/phlebitis secondary to IV line Note: Majority of cases can be treated with catheter removal and warm compress TID alone.	S. aureus, coagulase-negative staphylococci (including S. epidermidis)	If antibiotics required: ceFAZolin 1 g IV q8h^†
		β-lactam anaphylaxis or MRSA suspected: vancomycin (dose as per hospital guidelines)
Human bites^‡ Note: Give tetanus booster (Td) if none in the past 5 years.	S. aureus, Streptococcus spp., oral anaerobes, Haemophilus spp., Eikenella corrodens	Non-severe infections:
		amoxicillin/clavulanic acid 875 mg/125 mg PO q12h
		Severe infections:
		cefTRIAXone 1 g IV q24h + metroNIDAZOLE 500 mg PO/IV q12h
		piperacillin/tazobactam 3.375 g IV q6h
		β-lactam allergy (anaphylaxis): metroNIDAZOLE 500 mg PO/IV q12h + one of: moxifloxacin 400 mg PO/IV q24h OR doxycycline 100 mg PO q12h OR co-trimoxazole DS (trimethoprim [TMP] 160 mg/sulfamethoxazole [SMX] 800 mg) 2 tabs PO q12h
Animal bites (dogs and cats) Note: Give tetanus booster (Td) if none in the past 5 years, and consider rabies (Public Health Ontario – rabies)	S. aureus, Streptococcus spp., oral anaerobes, Pasteurella multocida^¶, Captnocytophaga canimorsus	Prophylaxis^§ (x3-5 days)
		amoxicillin/clavulanic acid 875 mg/125 mg PO q12h OR amoxicillin/clavulanic acid 500 mg/125 mg PO q8h
		Treatment (non-severe):
		amoxicillin/clavulanic acid 875 mg/125 mg PO q12h
		Treatment (severe):
		cefTRIAXone 1 g IV q24h + metroNIDAZOLE 500 mg PO/IV q12h
		piperacillin/tazobactam 3.375 g IV q6h
		β-lactam allergy (anaphylaxis): metroNIDAZOLE 500 mg PO/IV q12h + one of: moxifloxacin 400 mg PO/IV q24h OR doxycycline 100 mg PO q12h OR co-trimoxazole DS (trimethoprim [TMP] 160 mg/sulfamethoxazole [SMX] 800 mg) 2 tabs PO q12h

^* Severe soft tissue infections may require a combined medical and surgical approach. Consultation with Infectious Diseases and Surgical Services is recommended.

^† Consider ceFAZolin 2 g IV q8h for patients greater than 100 kg.

^‡ Human bites do not generally require prophylaxis, but can be considered if the wound is through the dermis, especially on the hand.

^§ Consider prophylaxis for animal bites if:

moderate to severe injury <8 hours old, especially if edema or crush injury
deep puncture wounds (especially due to cat bites)
hand wounds or in close proximity to a bone or joint (particularly prosthetic joints)
immunocompromised patients (including those with splenectomy, liver disease, or steroid therapy)
wounds requiring closure
wound is in the genital area.

^¶ Clinical failures have been noted in patients treated with first-generation cephalosporins (eg. cephalexin), and clindamycin. These agents have poor in vitro activity against P. multocida and should be avoided.

Duration of Therapy

Most cases of uncomplicated cellulitis can be managed using oral therapy alone. If intravenous therapy is needed initially (inability to take oral medications or early concern regarding aggressive infection), step-down to oral antibiotics should be considered within 48-72 hours. A total duration of therapy of 5-7 days is sufficient for most uncomplicated skin and soft tissue infections.

References

Stevens DL et al. Practice Guidelines for the Diagnosis and Management of Skin and Soft Tissue Infections: 2014 Update by the Infectious Diseases Society of America Clinical Infectious Diseases. Clin Infect Dis. 2014:1-43.
Stevens DL, Bisno AL, Chambers HF et al. Guidelines for Skin and Soft-Tissue Infections. Clin Infect Dis. 2005;41:1373-80.
Mermel LA, Farr BM, Sherertz RJ et al. Guidelines for the Management of Intravascular Catheter-Related Infections. Clin Infect Dis. 2001;32:1249-72.
Lipsky BA, Berendt AR, Cornia PB, Pile JC et al. Diagnosis and Treatment of Diabetic Foot Infections. Clin Infect Dis. 2012;54:132-173.
UpToDate. Wolters Kluwer Health. http://www.uptodate.com/contents/search (accessed July 22, 2017).