Infective Endocarditis (Antimicrobial)


What's New:
27/02/23: Please note changes to requirements of blood cultures. 

Discuss antibiotic choice with infection specialist

Advice from NHS Highland Cardiology Department and use of antibiotic prophylaxis prior to dental procedures is available under Dental.

For glossary of terms see Glossary


  • Endocarditis is a clinical diagnosis confirmed by appropriate microbiology. Early involvement of Microbiology, Cardiology and a clinician with expertise in infection is essential. 
  • If the patient’s clinical condition is already severe or deteriorating, start antibiotic therapy immediately after a minimum of 3 sets of blood cultures. DISCUSS ANTIBIOTIC CHOICE WITH INFECTION SPECIALIST.  If gentamicin is recommended, follow hospital gentamicin endocarditis guidelines.

Cardiology opinion and referral is required for ALL patients with endocarditis

  • A vital part of management of infective endocarditis is to get a causative organism to help guide management. This requires blood cultures to be taken OFF antibiotics. If patient is clinically stable then do NOT start antibiotics and take at least 3 sets of blood cultures, taken at least 30 minutes apart but preferably 12 hours apart. Do not wait for a fever before taking blood cultures.
  • Note a positive blood culture for Staphylococcus aureus requires a transthoracic echocardiogram and potential further discussion with a consultant cardiologist even in the absence of a murmur. National guidance on the management of Staphylococcus aureus bacteraemia in adults (SAB) is available.
  • Murmur and fever - suspect endocarditis.
  • ‘Normal’ echo [transthoracic (TTE) or transoesophageal (TOE)] does not exclude endocarditis.
  • TOE may help if TTE is ‘normal’ or if images are poor (e.g. lung disease, obesity).
  • TOE is unnecessary if TTE shows vegetations unless aortic valve endocarditis suspected.
  • If aortic valve endocarditis is suspected TOE should be considered routinely to look for abscess formation.
  • Deteriorating heart failure or rhythm instability despite antibiotic therapy should prompt an urgent cardiac/surgical assessment.
  • Delay in valve replacement can prove fatal.


  • Insert an intravenous cannula using aseptic technique and dress with topical povidone-iodine.
  • Always give antibiotic therapy intravenously.
  • Change the intravenous cannula every 48 hours.
  • Once the diagnosis has been confirmed and long-term IV antibiotic administration (>2 weeks) is required, arrange insertion of a PICC line or Hickman line using full surgical technique in the operating theatre.
  • Consider referral to Outpatient Parenteral Antimicrobial Therapy (OPAT) service.

Modified Dukes Criteria for the Diagnosis of Infective Endocarditis (IE)

MAJOR criteria

Blood culture positive for IE:

  • Typical microorganisms consistent with IE from 2 separate blood cultures:
    Viridans streptococci, Streptococcus bovis, HACEK group, Staphylococcus aureus; 
    or Community-acquired enterococci, in the absence of a primary focus; or
  • Microorganisms consistent with IE from persistently positive blood cultures, defined as follows:
    At least 2 positive cultures of blood samples drawn >12h apart; or
    All of 3 or a majority of >4 separate cultures of blood (with first and last sample drawn at least 1h apart)
  • Single positive blood culture for Coxiella burnetii or phase I IgG antibody titre >1 : 800

Evidence of endocardial involvement

  • Echocardiogram positive for IE
  • Vegetation – Abscess - New partial dehiscence of prosthetic valve
  • New valvular regurgitation

Minor criteria

  • Predisposition: predisposing heart condition, injection drug use
  • Fever: temperature >38°C
  • Vascular phenomena: major arterial emboli, septic pulmonary infarcts, mycotic aneurysm, intracranial haemorrhage, conjunctival haemorrhages, and Janeway lesions
  • Immunologic phenomena: glomerulonephritis, Osler’s nodes, Roth’s spots, rheumatoid factor
  • Microbiological evidence: positive blood culture but does not meet a major criterion or serological evidence of active infection with organism consistent with IE

Diagnosis of IE is definitive in the presence of

  • 2 major criteria, or
  • 1 major and 3 minor criteria, or
  • 5 minor criteria

Diagnosis of IE is possible in the presence of

  • 1 major and 1 minor criteria, or
  • 3 minor criteria

Adapted from Li JS, Sexton DJ, Mick N, Nettles R, Fowler VG, Jr., Ryan T, Bashore T, Corey GR. Proposed modifications to the Duke criteria for the diagnosis of infective endocarditis. Clin Infect Dis 2000;30:633–638.

Last reviewed: 27/02/2023

Next review date: 28/02/2026

Author(s): Antimicrobial Management Team.

Version: 7

Approved By: TAM subgroup of ADTC

Reviewer name(s): Alison Macdonald, Area Antimicrobial Pharmacist.

Document Id: AMT103

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