Is the MIC useful in deciding to treat endocarditis surgically?

The infecting pathogen and its susceptibility to antibiotics is used to suggest prognosis in endocarditis. A case study was performed in a tertiary referral cardiology centre to assess the contribution of the measurement of minimum inhibitory concentration (MIC) to the decision to treat endocarditis surgically. The records were examined of 125 patients admitted between 1981 and 1999 in whom the minimum inhibitory concentration for the pathogen had been measured. The measures of outcome were mortality at time of hospital discharge and at 6 months, surgical referral and cure by medical treatment. Endocarditis caused by Staphylococcus aureus with a raised MIC of flucloxacillin (methicillin) was associated with higher mortality even if glycopeptides were used in treatment (< or = 35 mg/l 0/7 versus MIC 1-2 mg/l 4/13, P = 0.01). Elevated MICs of flucloxacillin in S. aureus infection or of gentamicin in streptococcal disease were associated with surgical intervention. There were no significant differences between bacterial pathogens in mortality, surgical referral or cure by medical treatment. The measurement of MIC appears prognostically important in deciding the surgical management of endocarditis.