Skin & Soft Tissue Skin & Soft Tissue InfectionsInfectionsBrent Gunderson, PharmDInfectious Diseases Research FellowUniversity of MinnesotaCollege of PharmacyObjectivesObjectives❏Identify host factors that prevent skin and soft tissue infections, and factors that could predispose to infection❏Identify pathogens that commonly cause typical skin and soft tissue infections❏Suggest empiric antimicrobial therapy for typical skin and soft tissue infectionsIntroductionIntroduction❏ Skin/soft tissue infections are common and vary widely in severity» Can involve any or all layers of skin, fascia and muscle❏ Many classification systems, based on:» Infection local or diffuse» Systemic signs» Necrotizing» Infecting organism❏ Important to have an idea of what the infecting organism is, and determine appropriate empiric antibiotic therapy where necessarySkin Composition & Host Skin Composition & Host Defenses to InfectionDefenses to Infection❏ Multilayered construction of skin» Stratum corneum, epidermis, dermis, subcutaneous fat, superficial fascia❏ Skin is dry, continuously renewed❏ Limited epithelial cell adherence by pathogens❏ Intact stratum corneum (acts as a barrier)❏ Low skin pH (normally about 5.5)❏ Host immune system (IgA and IgG production in sweat)❏ Resident skin flora (competitive inhibition)Factors that Could Predispose Factors that Could Predispose to SSTIto SSTI❏ Damage to corneal layer allowing bacterial penetration❏High conc. of bacteria (>105)❏Excessive skin moisture❏Occlusion of blood supply to skin❏Obesity❏Blood dyscrasias❏Corticosteroid use❏Neutrophil function defects❏Paraperesis❏Diabetes❏Alcohol AbuseBacteria Associated with SSTIsBacteria Associated with SSTIs❏ Gram-positive» S. aureus, S. epidermidis» Streptococci spp.❏ Gram-negative» E. coli, Klebsiella, Proteus» Pasturella multocida❏ Anaerobes» Eikenella corrodens» Other oral anaerobes» Clostridium spp.» B. fragilisImpetigo & EcthymaImpetigo & Ecthyma❏ Pathogenesis» Bacteria invades normal skin via minor wounds (e.g., insect bites, abrasions), develops in approximately 10 days» More common in hot, humid, summer weather» Can be communicable»Spread facilitated by crowding, poor hygiene» Ecthyma similar to impetigo, but tends to penetrate through the epidermis❏ Bacteria» Usually group A streptococci» Occasionally S. aureusImpetigo & EcthymaImpetigo & Ecthyma❏ Clinical findings of impetigo» Small, superficial lesions: purulent discharge dries forming thick, golden yellow crusts» Occurs principally around mouth and nostrils❏ Clinical findings of ecthyma» Small, “punched-out” ulcers covered by greenish yellow crusts, extending deeply into the dermis and surrounded by raised margins»Most frequently in lower extremities»Particularly in children and elderly❏Lesions usually painless, but pruritus is common; can lead to spreading of the infectionImpetigoImpetigoImpetigo & EcthymaImpetigo & Ecthyma❏ Antimicrobial therapy (7-10 day duration)» β-lactams»PCN VK 25 – 50 mg/kg/day (250-500 mg) QID x10d»Single dose benzathine PCN G 300-600,000 U peds, 1.2 MU adults»Cephalexin 500 mg QID x10d»Cefaclor 500 mg TID x10d»Cefprozil 500 mg BID x10d» PCN allergy»Emycin 30-50 mg/kg/day (250-500 mg) QID x10d» Prophylaxis»Mupirocin or triple antibiotic ointment topically to lesions/insect bites can help prevent pyoderma, esp. if young children in close contact in outbreakCarbuncle & FuruncleCarbuncle & Furuncle❏Pathogenesis»Furuncle is acute inflammation of subcutaneous layers of skin, gland, or hair follicles»Carbuncle is more extensive extending into subcutaneous fat and developing into multiple abscessesCarbuncle & FuruncleCarbuncle & Furuncle❏Clinical findings»Furuncles » Occur in skin areas subject to friction and perspiration containing hair follicles (neck, face, buttocks)»Carbuncle» Larger, deeper, indurated lesion typically at nape of neck, on back, or on thighs» Often occur along the course of multiple hair follicles and may be associated with fever and malaise.CarbuncleCarbuncleCarbuncle & FuruncleCarbuncle & Furuncle❏ Etiology» S. aureus❏ Non-pharmacologic therapy» Furuncle»Most treated with moist heat, promoting localization and drainage of the process» Carbuncle/furuncle with surrounding cellulitis»Require antistaphylococcal antibiotic»Surgical drainage for large and fluctuant lesionsCarbuncle & FuruncleCarbuncle & Furuncle❏ Antimicrobial therapy» Oral»Cephalexin 500 mg QID x10d»Cefaclor 500 mg TID x10d»Cefprozil 500 mg BID x10d»Oxacillin 750 mg QID x10d» IV»Cefazolin 1-2 g q8h»Nafcillin 1-1.5 g q4h» PCN allergy»Clindamycin 150-300 mg PO QID x10d»Erythromycin 250-500 mg PO QID x10dErysipelasErysipelas❏ Pathogenesis» Bacterial invasion of normal skin via minor trauma (e.g., insect bites, abrasions), to form distinctive cellulitis with prominent lymphatic involvement❏ Clinical findings» Acute febrile disease with localized inflammation and redness of skin and subcutaneous tissue» Sharply demarcated bright red rash commonly affecting bridge of nose and cheeks» Associated with systemic symptoms: chills, fever, rigor, malaise» More common in infants, young children, elderly» Most commonly on face; also on extremities, genitaliaErysipelasErysipelas❏Etiology»Almost always S. pyogenes (group A)»Group B streptococci can be seen in newborns»Rarely S. aureusErysipelasErysipelas❏ Antimicrobial therapy (7-10 days; pts should improve dramatically in 24-48h)» Oral»PCN VK 25-50 mg/kg/d QID x10d (250-500 mg QID)»Dicloxacillin 500 mg QID»Cephalexin 500 mg QID x10d»Cefprozil 500 mg BID x10d» IV»PCN 1 MU Q6h IV»Cefazolin 1 g IV q8h»Nafcillin or oxacillin 2 g IV q4h» PCN allergy»Emycin 30-50 mg/kg/day (250-500 mg) QID PO x10dCellulitisCellulitis❏ Pathogenesis» Previous trauma (laceration, puncture wound) or underlying skin lesion (furuncle, ulceration) predisposes development of cellulitis» Acute spreading of infection of the skin extending deeper than erysipelas to involve the subcutaneous tissues» Inflammation spreads through the tissue❏ Value of culture» Not usually positive (only in 15-25% of patients)» More necessary in IVDA, who might be bacteremic» Also, immunocompromised patients, previous failure, hospitalized patientsCellulitisCellulitis❏ Clinical findings» Within hours to days of inciting trauma, have local tenderness, pain, erythema, develop and rapidly