Chapter 118. Infective Endocarditis (Part 9)

Other Organisms In the absence of meningitis, endocarditis caused by Streptococcus pneumoniae with a penicillin MIC of ≤1.0 can be treated with IV penicillin (4 million units every 4 h), ceftriaxone (2 g/d as a single dose), or cefotaxime (at a comparable dosage). Infection caused by pneumococcal strains with a penicillin MIC of ≥2.0 should be treated with vancomycin. Until the strains susceptibility to penicillin is established, therapy should consist of vancomycin plus ceftriaxone, especially if concurrent meningitis is suspected. P. aeruginosa endocarditis is treated with an antipseudomonal penicillin (ticarcillin or piperacillin) and high doses of tobramycin (8 mg/kg...
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Chapter 118. Infective Endocarditis (Part 9) Chapter 118. Infective Endocarditis (Part 9) Other Organisms In the absence of meningitis, endocarditis caused by Streptococcuspneumoniae with a penicillin MIC of ≤1.0 can be treated with IV penicillin (4million units every 4 h), ceftriaxone (2 g/d as a single dose), or cefotaxime (at acomparable dosage). Infection caused by pneumococcal strains with a penicillinMIC of ≥2.0 should be treated with vancomycin. Until the strains susceptibility topenicillin is established, therapy should consist of vancomycin plus ceftriaxone,especially if concurrent meningitis is suspected. P. aeruginosa endocarditis istreated with an antipseudomonal penicillin (ticarcillin or piperacillin) and highdoses of tobramycin (8 mg/kg per day in three divided doses). Endocarditis causedby Enterobacteriaceae is treated with a potent β-lactam antibiotic plus anaminoglycoside. Corynebacterial endocarditis is treated with penicillin plus anaminoglycoside (if the organism is susceptible to the aminoglycoside) or withvancomycin, which is highly bactericidal for most strains. Therapy for Candidaendocarditis consists of amphotericin B plus flucytosine and early surgery; long-term (if not indefinite) suppression with an oral azole is advised. Caspofungintreatment of Candida endocarditis has been effective in sporadic cases;nevertheless, the role of echinocandins in this setting has not been established. Empirical Therapy In designing and executing therapy without culture data (i.e., before cultureresults are known or when cultures are negative), clinical and epidemiologic cluesto etiology must be weighed, and both the pathogens associated with the specificendocarditis syndrome and the hazards of suboptimal therapy must be considered.Thus, empirical therapy for acute endocarditis in an injection drug user shouldcover MRSA and gram-negative bacilli. The initiation of treatment withvancomycin plus gentamicin immediately after blood is obtained for culturescovers these as well as many other potential causes. In the treatment of culture-negative episodes, marantic endocarditis must be excluded and fastidiousorganisms sought serologically. In the absence of confounding prior antibiotictherapy, it is unlikely that S. aureus, CoNS, or enterococcal infection will presentwith negative blood cultures. Thus, in this situation, these organisms are not thedeterminants of therapy for subacute endocarditis. Pending the availability ofdiagnostic data, blood culture–negative subacute native valve endocarditis istreated with ceftriaxone plus gentamicin; these two antimicrobial agents plusvancomycin should be used if prosthetic valves are involved. Outpatient Antimicrobial Therapy Fully compliant patients who have sterile blood cultures, are afebrile duringtherapy, and have no clinical or echocardiographic findings that suggest animpending complication may complete therapy as outpatients. Careful follow-upand a stable home setting are necessary, as are predictable IV access and use ofantimicrobial agents that are stable in solution. Monitoring Antimicrobial Therapy The serum bactericidal titer—the highest dilution of the patients serumduring therapy that kills 99.9% of the standard inoculum of the infectingorganism—is no longer recommended for assessment of standard regimens.However, in the treatment of endocarditis caused by unusual organisms, thismeasurement, although not standardized and difficult to interpret, may provide apatient-specific assessment of in vivo antibiotic effect. Serum concentrations ofaminoglycosides and vancomycin should be monitored. Antibiotic toxicities, including allergic reactions, occur in 25–40% ofpatients and commonly arise during the third week of therapy. Blood tests todetect renal, hepatic, and hematologic toxicity should be performed periodically. In most patients, effective antibiotic therapy results in subjectiveimprovement and resolution of fever within 5–7 days. Blood cultures should berepeated daily until sterile, rechecked if there is recrudescent fever, and performedagain 4–6 weeks after therapy to document cure. Blood cultures become sterilewithin 2 days after the start of appropriate therapy when infection is caused byviridans streptococci, enterococci, or HACEK organisms. In S.aureus endocarditis, β-lactam therapy results in sterile cultures in 3–5 days,whereas positive cultures may persist for 7–9 days with vancomycin treatment.When fever persists for 7 days despite appropriate antibiotic therapy, patientsshould be evaluated for paravalvular abscess and for extracardiac abscesses(spleen, kidney) or complications (embolic events). Recrudescent fever raises thequestion of these complications but also of drug reactions or complications ofhospitalization. Serologic abnormalities (e.g., in C-reactive protein level,erythrocyte sedimentation rate, rheumatoid factor) resolve slowly and do notreflect response to treatment. Vegetations become smaller with effective therapy,but at 3 months after cure half are unchanged and 25% are slightly larger. Surgical Treatment Intracardiac and central nervous system complications of endocarditis areimportant causes of morbidity and death associated with this infection. In somecases, effective treatment for these complications requires surgery. Most of theclinical indications for surgical treatment of endocarditis are not absolute (Table118-5). The risks and benefits as well as the timing of surgical treatment musttherefore be individualized (Table 118-6).