The Registrar mentioned that the patient had been on antibiotic prophylaxis since the operation, and they wondered whether it should stop after 24 hours.
“It’s not prophylaxis” said the Microbiologist.
“Yes, it is” replied the Registrar, “the Surgeons have written that they want the antibiotic prophylaxis to continue, but they haven’t said for how long.”
“No, it’s not prophylaxis” said the Microbiologist again, “it’s treatment. They are different things with different purposes”.
“Oh, here we go” muttered the Registrar, “pedantics again!”
“I heard that!” Exclaimed the Microbiologist, smiling, at least he knew someone had read his blog. “Let me explain…” he said in that manner of, shhh…listen!
The Registrar groaned inwardly, knowing a mini-lecture was coming and there was nothing he could now do to stop it…
Prophylaxis is the use of antibiotics to prevent infection of a previously uninfected site. There are 2 types of prophylaxis, primary and secondary:
- Primary prophylaxis - aims to prevent initial infection e.g. surgical prophylaxis, duration usually required for <24 hours, whilst ongoing entry of bacteria into sterile body sites e.g. at the time of surgery
- Secondary prophylaxis - aims to prevent recurrent episodes of infection, duration usually requires long courses of antibiotics at reduced doses e.g. post-splenectomy, rheumatic fever, recurrent UTIs in children
Treatment is the use of antibiotics to eliminate infection from an already infected site. Treatment and duration of treatment varies between clinical conditions.
Types of surgery
When considering whether to give antibiotics as primary prophylaxis to cover a surgical procedure it is important to think about what it is you are trying to achieve with those antibiotics. It helps to split surgical situations into four categories:
- Ultraclean – risk of infection <0.3% - this type of surgery is often done in an ultraclean operating theatre with HEPA filtered air being blown directly down over the patient and surgical team, and extracted away, without any airborne contamination being able to settle in the operative site. This is often used for operations where implants are being inserted and where post-operative infection is either life-threatening or requires further surgery e.g. heart valve replacements, prosthetic joint insertion – antibiotic prophylaxis given for 24 hours to prevent infection secondary to bacteria getting into the operative site during the procedure
- Clean – risk of infection 3% - the operation involves sterile tissue where the overlying surface has been cleaned and the risk of infection is very low, and the consequence of post-operative infection is minor e.g. removal of a skin lump – no antibiotic prophylaxis required
- Clean-contaminated – risk of infection 13% - the operation involves a site where the number of bacteria has been reduced as much as possible pre-operatively but which still contains bacteria that can leak out during the operation e.g. planned elective surgery on the bowel which has been emptied pre-operatively using laxatives and enemas, or leakage occurs during the operation but it is immediately controlled and the contaminated area cleaned – antibiotic prophylaxis given for 24 hours to deal with small amounts of bacterial leakage during the operation
- Contaminated – risk of infection >40% - operative site heavily contaminated with micro-organisms pre-operatively e.g. perforated appendix or bowel with faecal soiling into the abdomen or traumatic injury with environmental contamination from soil – antibiotic TREATMENT required, this is no longer a prophylaxis situation as the infection is already established
Endocarditis prophylaxis is a somewhat controversial topic in medicine. It’s essentially one of these areas where there is no good evidence either way. Most hospitals have their own guidelines for antibiotic prophylaxis to prevent endocarditis in at-risk patients undergoing certain procedures. There is a guideline from the National Institute for Health and Care Excellence (NICE) that now suggests “considering” antibiotic prophylaxis to prevent endocarditis but NICE does not give specific recommendations… basically they have shifted responsibility to the prescriber which isn’t overly helpful in my opinion.
The following is based upon the American Heart Association Guidelines, and is based on risk factors in patients PLUS risk factors associated with the type of procedure they are having. REMEMBER endocarditis is rare therefore there is insufficient evidence to draw firm conclusions on prophylaxis. Many Microbiologists and Cardiologists believe “absence of evidence does not mean evidence of absence” and as endocarditis is a life-threatening infection prevention is more effective than treatment.
- Previous infective endocarditis
- Prosthetic heart valve
- Acquired valvular heart disease with stenosis or regurgitation
- Cyanotic congenital heart disease
At-Risk Patients who are undergoing the Following Procedures:
- Dento-gingival manipulation or endodontics
- Surgery to the jaw and oral cavity
- Tonsillectomy and adenoidectomy
- Respiratory tract procedures with incision or biopsy of the respiratory mucosa
PO Amoxicillin 3g
OR IV Amoxicillin 2g
2nd line (if 1st line contraindicated OR recent treatment with Beta-lactam antibiotics)
PO Clindamycin 450mg OR IV Clindamycin 600mg
“Five days” replied the Microbiologist, smiling and moving on to the next patient.
The Registrar rolled his eyes to the ceiling behind the Microbiologists back and muttered under his breath “why didn’t you just say that?”
“Because I’m a Microbiologist and a pedant” called back the Microbiologist turning back and grinning at the Registrar, “now come on I haven’t got all day!”