HOW TO INTERPRET CULTURE RESULTS Karen Brust, MD November 29, 2012
DISCLOSURES NONE
CULTURE RESULTS Based on susceptibility patterns CLSI: international, interdisciplinary, Nonprofit, standards developing, & Educational organizations
CULTURE RESULTS CLSI outlines guidelines based on research data Includes in vitro data, pharmacokinetics/ dynamics of the drugs, and clinical studies CLSI establishes interpretive criteria CLSI performs quality controls CLSI adjusts their own guidelines yearly based on the changing susceptibilities
CULTURE RESULTS WHAT IS AN MIC Minimum Inhibitory Concentration It is the lowest concentration of drug that will inhibit growth of an organism after an overnight incubation
CULTURE RESULTS WHAT IS THE BREAKPOINT An MIC or zone diameter value used to indicate susceptible, intermediate, and resistant susceptible = using the dose of abx used to treat the site of infection, the organism is killed by the usual, achievable concentrations intermediate = may be clinically effective IF the drug concentrates more readily at the site of infection resistant = organism not killed at the usual achievable levels
CULTURE RESULTS DEFINITIONS OF REPORTED INTERPRETATIONS FDA vs CLSI Other governing bodies, worldwide Example: CLSI has no definitive data regarding Tigecycline breakpoint in the treatment of a CR- Klebsiella Pneumoniae. FDA defines < 2 as susceptible
GENERAL RULES FOR INTERPRETATION The lowest number does not always mean the most potent drug Pharmacokinetics/ dynamics of the drug play into reporting an MIC Based on the clinical scenario and germ #1: pick the ideal antibiotic in that situation #2: If that abx is susceptible, consider your patient and whether that choice is appropriate (Drug allergies? Renal function? Liver function? Drug interactions?)
CASE #1 HISTORY OF PRESENT ILLNESS: 51-year-old white male with uncontrolled diabetes (Hg A1C 15.5) and tobacco abuse; admitted for treatment of diabetic foot infection 3 wk hx of left lateral wart that 2 weeks ago popped and drained ; over last week his arch turned blackish-purple and the drainage became foul-smelling; 1 day PTA he had subjective fever and rigors ALLERGIES: PCN, which causes anaphylaxis. Occurred as a child and he remembers the hospitalization INPATIENT ANTIBIOTICS: Include 1. IV vancomycin. 2. IV Cipro. 3. IV flagyl
CASE #1 PHYSICAL EXAM: - Notable for a bandaged foot, 2/6 SEM best at RUSB, splinter hemorrhages of right hand and right conjunctival hemorrhage DATA: Blood cx 2/2 (+) for steptococcus species, non-viable for susceptibilities And, as usual polymicrobial swab of draining wound collected in ER: (1) sensitive e. coli (2) sensitive p. vulgaris (3) sensitive s. aureus (4) corynebacterium
CASE #1 OPERATIVE CULTURES
CASE #1 TREATMENT OPTIONS More data: TEE positive for AoV vegetation Correct assessment: immunosuppressed male w/ DM foot infection and bacteremia with dissemination and Aortic Valve Infective endocarditis Plan? Ertapenem for 2 weeks then finish course for AoIE w/ Ceftriaxone ****Remember PCN allergy? He admitted to taking Keflex w/out issue
CASE #2 76 y/o WM w/ fairly well controlled DM, neuropathy, htn, hchol, CAD w/ stenting seen in clinic for podiatrist s concern for osteomyelitis He is s/p TMA on left in 2002. 18 mos ago developed lateral ulceration. 2 weeks ago the bone became exposed. Plain film showed osteomyelitic changes of the 4 th and 5th metatarsal remnants Denies f/c/ sweats. Otherwise, no complaints ALLERGIES: augmentin causes nausea and diarrhea OUTPATIENT ABX: none PE: afebrile, VSS, exam otherwise non-revealing w/ exception of lateral ulceration that probes to bone (no cellulitis, etc)
CASE #2
CASE #2 TREATMENT OPTIONS: (1) IV Vanc x 6 weeks (or shorter) followed by doxy for x period of time (2) PO bactrim vs PO doxy for extended period of time (3) amputation
QUESTIONS?