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Infective Endocarditis

Bloodstream

Source: IDMP View on spectrum chart →
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Clinical scenario / source

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1. Clinical Syndrome

Infection of endocardial surface, classically valvular but can involve mural endocardium, prosthetic material, or intracardiac devices.

Subtypes drive empiric choice:

  • Native valve (NVE) — community-acquired, often subacute, viridans strep / S. aureus / enterococcus dominant.
  • Prosthetic valve (PVE) — early (<1 yr post-op, CoNS / S. aureus / GNR / fungi) vs late (≥1 yr, mimics NVE).
  • CIED-related (pacemaker / ICD) — S. aureus + CoNS dominant.
  • IVDU-associated — right-sided (tricuspid), S. aureus dominant; left-sided IE in IVDU still common.

Excludes: culture-negative IE workup (Bartonella, Coxiella, Brucella — separate workup), non-infective vegetations (marantic, Libman-Sacks).

2. Pathogens

Consider the patient: Age (older → enterococcus from GU, S. gallolyticus from colon), valve status (native vs prosthetic, early vs late post-op), IVDU (S. aureus dominant, tricuspid disease), recent dental/GI/GU procedure (VGS, enterococcus, Strep gallolyticus), CIED, healthcare exposure (CoNS, MRSA).

Consider the case: Acute fulminant (S. aureus, group B strep) vs subacute indolent (VGS, enterococcus, HACEK, culture-negative). Embolic phenomena, persistent bacteremia despite appropriate abx, evidence of heart failure or abscess → surgical consideration.

Common

Less common

3. Empiric Therapy

TierFirst choiceAlternativesDurationComments
Acute / severe
  • load + AUC-guided (target 15–20) · — · IV · Empiric until cultures + MIC
  • 2 g · q4h · IV · Empiric — covers enterococcus + most strep + Listeria.
  • Daptomycin + ampicillin 10 mg/kg dapto + 2 g amp q4h · — · IV

    Vanco alternative — useful for MRSA with rising MIC or vanco intolerance.

Empiric — 4–6 weeks total once organism identified (counted from first negative culture for S. aureus / fungi)**Native valve, hemodynamically unstable / sepsis** — empiric while cultures pend. Covers VGS, S. aureus (MR + MS), enterococcus. Add gentamicin only if enterococcus identified.
Admitted to ward
  • load + AUC-guided · — · IV · Empiric until cultures + MIC
  • 2 g · q24h · IV · Empiric — covers VGS, MSSA, HACEK.
  • 3 g · q6h · IV

    Alternative empiric for subacute community-acquired NVE — covers strep, enterococcus, HACEK.

4 weeks (PCN-S VGS, MIC ≤0.12, NVE) up to 6 weeks (PVE, S. aureus, enterococcus, MIC >0.12 VGS)**Subacute native-valve IE** — covers VGS, S. aureus, HACEK while awaiting cultures. Once organism identified, narrow per directed-therapy block.
ICU — Pseudomonas risk
  • load + AUC-guided · — · IV
  • 1 mg/kg · q8h · IV

    Synergistic dosing for CoNS / S. aureus PVE during first 2 weeks.

  • Vanc + cefepime + rifampin — · — · IV

    **Prosthetic valve early empiric.** Add rifampin 300 mg q8h after blood cultures stable (avoid early — selects resistance in high-burden bacteremia). Rifampin essential for biofilm penetration on prosthetic material.

6 weeks minimum for PVE (rifampin × 6 wks; gentamicin × first 2 wks only)**Prosthetic valve IE empiric** — covers CoNS, S. aureus, GNR. Surgery often required, especially with abscess, dehiscence, or persistent bacteremia. Discuss with cardiothoracic surgery early.

Add coverage if:

MRSA coverage
  • Healthcare-associated bacteremia
  • IVDU in MRSA-prevalent region
  • Known MRSA colonization
  • Prior MRSA infection

Add:

  • load + AUC-guided · — · IV · 6 weeks from first negative culture
VRE coverage
  • Healthcare-associated enterococcal bacteremia
  • Prior VRE colonization
  • Liver transplant
  • Prolonged hospitalization with broad-spectrum abx

Add:

  • 10–12 mg/kg · q24h · IV

    Higher dose than for SSTI to overcome vegetation burden. Linezolid is alternative but bacteriostatic.

  • 600 mg · q12h · IV/PO

    Bacteriostatic — less favored for IE but salvage option.

Pseudomonas coverage
  • IVDU (right-sided IE)
  • Recent broad-spectrum abx
  • Healthcare-associated

Add:

  • 2 g · q8h · IV
  • 4.5 g · q6h · IV

    Alternative anti-pseudomonal beta-lactam.

4. Directed Therapy

Native valve VGS, PCN-susceptible (MIC ≤0.12):

  • PCN-G 12–18 MU/d IV continuous or q4h × 4 weeks, OR
  • Ceftriaxone 2 g q24h × 4 weeks (OPAT-friendly), OR
  • PCN/CTX + gentamicin 3 mg/kg/d × 2 weeks (short-course combo).

Native valve VGS, MIC 0.12–0.5:

  • PCN-G 24 MU/d + gentamicin × 2 weeks, then PCN alone × 2 more weeks.

Native valve VGS, MIC >0.5:

  • Treat as enterococcus (PCN/amp + gent or amp + CTX).

Native valve MSSA: Nafcillin 2 g q4h × 6 weeks (or cefazolin 2 g q8h — equivalent efficacy, better tolerated). NO routine gentamicin for native-valve S. aureus IE.

Native valve MRSA: Vancomycin AUC-guided × 6 weeks. Daptomycin 10 mg/kg if vanc intolerance or MIC creep.

Enterococcus faecalis (susceptible): Ampicillin 2 g q4h + ceftriaxone 2 g q12h × 6 weeks (AHA 2015 preferred — equivalent efficacy, no nephrotoxicity vs amp + gent).

Prosthetic valve VGS: Same MIC tiers as NVE but extend to 6 weeks; add gentamicin × first 2 weeks for MIC >0.12.

Prosthetic valve MSSA: Nafcillin + rifampin × 6 weeks + gentamicin × first 2 weeks. Start rifampin only after blood cultures clear (avoids resistance).

Prosthetic valve MRSA: Vanc + rifampin × 6 weeks + gentamicin × first 2 weeks.

Surgical indications (AHA 2015): heart failure from valvular dysfunction, fungal IE, abscess / fistula, persistent bacteremia (>5–7 days on appropriate abx), recurrent embolic events, large vegetations (>10 mm) with embolism, S. aureus PVE.

5. Monitoring

Resolution: repeat blood cultures q24–48h until clear (essential for S. aureus / fungal — duration of therapy counted from first negative). Defervescence usually 5–7 days; persistent fever → re-image (TEE), look for abscess, embolic phenomenon, alternative source.

Imaging: TTE on presentation; TEE if TTE non-diagnostic, prosthetic valve, suspected abscess (sensitivity >90%). Duke 2023 criteria now incorporate ¹⁸F-FDG PET-CT for PVE and CIED.

Toxicity: vanc AUC + Cr q48h; gentamicin trough <1 + audiogram if prolonged; rifampin → orange secretions, hepatotoxicity, prolific drug interactions (warfarin, immunosuppressants).

Pearls

Cultures before antibiotics — 3 sets from separate sites over 30+ min if subacute, 2 sets if acutely septic. Duke 2023 criteria added prosthetic surgery + CIED material as predisposing, ¹⁸F-FDG PET-CT and CT angiography as major imaging criteria. Strep gallolyticus (formerly bovis biotype I) IE → colonoscopy to evaluate for colorectal CA. Don't routinely use gentamicin for native-valve S. aureus IE — AHA 2015 removed this recommendation. For enterococcus, amp + CTX preferred over amp + gent. Right-sided IVDU IE without complications can sometimes use shorter courses (2 weeks of nafcillin or oxacillin + gentamicin) — but only with strict criteria (susceptible MSSA, no metastatic infection, no LV involvement).

References