Transcript How to prescribe antibiotics: maybe it’s not as simple as

Microbiology Nuts & Bolts
Test Yourself – Skin & Bone
Begin here
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The patient in this test yourself case is
entirely fictitious, however it is based
on many clinical scenarios the author
has come in to contact with during his
medical career. Any similarity to a real
case is entirely coincidental.
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George
• 69 year old man
• Presents with a painful swollen left knee 1 year
after a total knee replacement
• He has a normal temperature, heart rate and
blood pressure
• On examination there is a large effusion in the
knee joint
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How should George be managed?
Choose A, B, C or D for the answer you feel best
fits the question
A
B
C
D
Start antibiotics for presumed septic arthritis
Aspirate the joint and withhold antibiotics
Aspirate the joint and start antibiotics
Replace the prosthesis
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Correct
• Answer: Aspirate the joint and withhold antibiotics
• It is likely that George has a chronic infection in his knee
prosthesis but it is not urgent to start treatment
immediately
• Withholding the antibiotics at this stage allows the
diagnosis of septic arthritis to be proven and antibiotic
treatment to be tailored to treat whatever bacteria is
causing the infection
• Different bacteria require different antibiotics and also
often different surgical strategies, and this can only be
decided once the bacterium is known
• If George were very unwell, and showing signs of sepsis,
then empirical treatment should be started as soon as the
joint had been aspirated
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George
• The synovial fluid was sent to the laboratory and
the Gram film was reported as showing Grampositive cocci in clumps
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What is the likely identification of the
bacterium causing the septic arthritis?
Choose A, B, C or D for the answer you feel best
fits the question
A
B
C
D
Staphylococcus aureus
Streptococcus pyogenes
Coagulase-negative Staphylococcus
Escherichia coli
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Correct
• Answer: Coagulase-negative Staphylococcus
• The presence of Gram-positive cocci in clumps suggests a
Staphylococcus spp. in the synovial fluid, but the length of time
the prosthesis has been in and the lack of systemic symptoms
and signs of infection make Staphylococcus aureus less likely
than a Coagulase-negative Staphylococcus
• S. aureus is an aggressive bacterium associated with severe
infections, systemic symptoms and signs, and often sepsis
• Coagulase-negative Staphylococci cause more indolent and
chronic infections and do not normally trigger a severe systemic
response
• S. pyogenes is a Gram-positive coccus that forms chains and E.
coli is a Gram-negative bacillus
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Which of the following antibiotics could
now be started empirically?
Choose A, B, C or D for the answer you feel best
fits the question
A
B
C
D
Flucloxacillin
Flucloxacillin PLUS Benzylpenicillin
Meropenem
Teicoplanin
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Correct
• Answer: Teicoplanin
• Vancomycin would be a suitable alternative as it is also a
glycopeptide antibiotic
• The glycopeptides are the most commonly used antibiotics in the
UK which are reliable first line empirical treatment of infections
caused by Coagulase-negative Staphylococci
• It may not be necessary to start antibiotic treatment
immediately the Gram film is known as ultimately the correct
treatment of George involves removal of the infected prosthesis
as well as antibiotics
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George
• The orthopaedic surgeons plan on taking George
to theatre the next day and ask what specimens
the laboratory would like
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How many specimens at least would
you recommend the surgeons take?
Choose A, B, C or D for the answer you feel best
fits the question
A
B
C
D
5
1
3
8
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Correct
• Answer: 5
• It is recommended that orthopaedic surgeons take at least 5
separate specimens when replacing a prosthetic joint that might
be infected
• The result of the culture is considered positive if the same
bacterium grows from at least 3 of the 5 samples
• If less than 3 samples are positive it might be due to
contamination of the samples with skin flora, or the patient may
have been inadvertently given a dose of antibiotics before the
operation which stopped the bacteria from growing and has
therefore made it difficult to diagnose the infection
• Remember: it is always best to wait for samples to be taken
before giving antibiotics if at all possible
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George
• George has his prosthesis removed and an
antibiotic impregnated spacer put in to his knee
• All of his operative samples grow
Staphylococcus epidermidis sensitive to
Teicoplanin, Ciprofloxacin and Rifampicin
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What initial treatment would you
recommend for George?
Choose A, B, C or D for the answer you feel best
fits the question
A
B
C
D
PO Ciprofloxacin PLUS PO Rifampicin
IV Teicoplanin PLUS PO Ciprofloxacin
IV Teicoplanin PLUS IV Rifampicin
IV Teicoplanin PLUS PO Rifampicin
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Correct
• Answer: IV Teicoplanin PLUS PO Rifampicin
• The correct initial treatment phase for this type of
infection is with 6 weeks of IV therapy (Teicoplanin) with
PO Rifampicin in addition
• After the initial 6 week phase it is appropriate to change
to a further 6 weeks of a highly bioavailable combination
of oral antibiotics which in this case could be Ciprofloxacin
PLUS Rifampicin
• The total duration of treatment would be 12 weeks before
considering putting a prosthetic knee back in to George
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George
• George was given 12 weeks in total of
antibiotics before plans were made to reinsert a
prosthetic knee
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What blood tests should be monitored
whilst George is on antibiotics?
Choose A, B, C or D for the answer you feel best
fits the question
A
B
C
D
FBC,
FBC,
FBC,
FBC,
U&Es
U&Es, LFTs
U&Es, LFTs, Teicoplanin levels
U&Es, LFTs, INR, Teicoplanin levels
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Correct
• Answer: FBC, U&Es, LFTs, Teicoplanin levels
• Long-term high dose Teicoplanin can suppress bone marrow
function causing a fall in white blood cell counts, platelets and
haemoglobin, therefore a weekly full blood count should be
done
• Teicoplanin can also cause renal failure and so weekly Urea and
Electrolytes should be checked
• Teicoplanin levels should be done every week to ensure the
levels are adequate to treat a bone and joint infection as well as
to make sure the levels are not toxic
• Rifampicin can cause hepatitis and so liver function tests should
be monitored weekly
• It is important that someone takes responsibility for ensuring
these tests are done as well as the results checked and any
appropriate actions are taken
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How long should George be off
antibiotics before his 2nd operation?
Choose A, B, C or D for the answer you feel best
fits the question
A
B
C
D
1
2
3
4
week
weeks
weeks
weeks
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Correct
• Answer: 2 weeks
• It is recommended that patients should be off antibiotics for at
least 2 weeks between stopping treatment for an infected
prosthetic joint and reinsertion of a new prosthesis
• This allows any residual bacteria to grow back by the time of
surgery in sufficient numbers to be detectable by the
microbiology laboratory in samples taken at the second
operation
• If these samples are positive then antibiotics can be continued
for a further 6-12 weeks depending on the bacterium grown
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George
• The samples taken at the 2nd stage operation
are culture negative and George is eventually
discharged from hospital
• Unfortunately his surgical wound continues to
ooze post-operatively after he returns home
• A few weeks later the wound starts to
breakdown from the outside inwards and he
goes on to develop a sinus leading in to the joint
space
• A further prosthetic joint infection is diagnosed
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Which of the treatment options should
NOT be used to treat this infection?
Choose A, B, C or D for the answer you feel best
fits the question
A
B
C
D
Long-term antibiotic suppression
Permanent resection arthroplasty
Two-stage revision arthroplasty
Debridement & retention of prosthesis (DAIR)
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Correct
• Answer: Debridement & retention of prosthesis (DAIR)
• In DAIR the infected prosthesis is cleaned and as much infected
material removed as possible
• All of the other treatment options could be considered but DAIR
is contraindicated by the presence of a sinus because the
infection will not be treated or suppressed by this method
• It is not unreasonable to give long-term antibiotic suppression to
patients in this circumstance if surgery is not an option, as the
antibiotics can prevent worsening of the infection or secondary
complications such as sepsis even if they have no hope of curing
the infection
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George
• The fluid oozing from Georges wound was sent
to the microbiology laboratory and an
Enterobacter cloacae was cultured
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What type of bacterium is
Enterobacter cloacae?
Choose A, B, C or D for the answer you feel best
fits the question
A
B
C
D
Gram-negative bacillus
Gram-positive coccus
Gram-negative coccus
Gram-positive bacillus
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Correct
• Answer: Gram-negative bacillus
• Enterobacter cloacae is a Gram-negative bacillus which
likes to colonise moist sites, including inadequately
healing post-operative wounds
• This bacterium does not normally cause skin and bone
infections, but if allowed to colonise a prosthetic joint
because there is a sinus that allows it to enter the joint
then it can do so (as can any Gram-negative bacillus)
• E. cloacae is often resistant to many antibiotics due to the
presence of a chromosomal AmpC enzyme causing
resistance to many of the Beta-lactam antibiotics,
although carbapenems such as Ertapenem, Imipenem and
Meropenem usually remain active
• Prosthetic joint infections with Gram-negative bacilli are
often very difficult to treat
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George
• In the end George opted for permanent
resection arthroplasty and the hip joint was
removed
• George was left with reduced function in his
knee and was unable to walk far without walking
sticks
The End
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