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Antibiotics

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Antibiotics
Antibiotics
Judith Coombes, University of
Queensland
General Principles
• Establish the need for antibiotic therapy
• When not to prescribe
–
–
–
–
–
Viral or minor bacterial disease
Viral diarrhoea
Sore throat
Sinusitis
Common cold
Are self limiting
Common cold needs common sense campaign
Antibiotic treatment can be
• Prophylactic antibiotics prevent serious infection in
specific situations (e.g. preventing the spread of
meningococcal disease).
• Presumptive antibiotic therapy is indicated in some
circumstances (e.g. a human bite to the hand
• Use empirical antibiotic therapy — which is aimed at the
likely causative organism — to manage an infection until
microbiological culture and susceptibility results are
known
• When the cause of an infection is confirmed, directed
therapy is aimed at the specific pathogen.
MIND ME
M
I
N
D
microbiology guides therapy wherever possible
indications should be evidence-based
narrowest spectrum required
dosage appropriate to the site and type of
infection
M minimise duration of therapy
E ensure monotherapy in most situations
5 Antibiotics
• Benzylpenicillin or Amoxycillin
– Streptococcis
• Cloxacillin
– Staphylococcis
• Vancomycin
– MRSA
• Gentamicin
– Pseudomonas
• Metronidazole
– anaerobes
Skin and Soft Tissue
Condition
Organism
Antibiotic
Duration
Wound
infections
surgical or
trauma
Staphylococcus
aureas
Cloxcillin
5 days
Cellulitis
Streptococcus
pyogenes
Cloxacillin
500mg q6h
7-14 days
Diabetic foot
ulcer
Anaerobic,
Metronidazole
mixed g +ve and 400mg q2h +
g-ve
Cephalxin
500mg q6h
Depends on
response
UTI
Condition
Antibiotic
Duration
Cystitis in men + E coli, ebsiella,
non pregnant
Enterococcus
women
faecalis, proteus
mirabilis
Trimethoprim
300mg daily or
Amoxycillin/clav
ulanate 875/125
q12h
W 3 days men
14 days
W 5 days men
a4 days
Catheter
associated
infections
Only treat if
symptoms,
change catheter
Cystitis in
pregnant
women
Organism
As above
Cephalexin
500mg q12h
10-14 days
Cardiovascular
Condition
Organism
Antibiotic
Duration
Endocarditis
empiric
Viridans
streptococci
other
streptococci
Enterococci
Staphylococci
Benzylpenicillin
1.8 g iv q4h +
cloxacillin 2g iv
q4h plus
gentamicin 46mg/kg/day iv
Modify as soon
as organism
and sensitivity is
known
Respiratory
Condition
Organism
Antibiotic
Community
acquired
pneumonia
mild
Strep.
Pneumonia
Haemophyllis
influenzie
Amoxycillin 1g
q8h +
Roxithramycin
300mg daily
Moderate
BenzylPenicillin
1.2g q6h +
Roxithramycin
300mg daily
severe
Azithromycin
500mg iv +
gentamicin 4-6g
daily +
Benzylpenicillin
1.2g q6h
Duration
CNS
Condition
Organism
Antibiotic
Duration
Suspected
bacterial
Meningitis
Neiserria
meningitis,
Strep.
Pneumonia,
Haemophilus
influenzae
Ceftriaxone 4g
iv daily (OR 2g
bd)
7-21 days
Prophylaxis if
known
Neiserria
meningitis,
Haemophilus
influenzae
Rifampicin
600mg daily
2 days
Sepsis- definition
• In adults and older children, severe sepsis
is the systemic response to an infection
manifested by organ dysfunction,
hypoperfusion or hypotension combined
with 2 or more of the following:
– fever,
– tachycardia,
– tachypnoea,
– elevated white cell count
Sepsis
Condition
Organism
Antibiotic
Duration
Sepsis
Psuedomonas
has high
morbidity
Cloxacillin 2g
q4-6h +
Gentamicin 46mg/kg dose 1
then adjust
2 days then add
Neutropenic
sepsis
Pseudomonas
Gentamicin 4most dangerous 6mg/kg/day
Ticarcillin/Clavul
anate 3.1g q6h
Suspect staph- Vancomycin 1g
skin wound or at q12h
48 hrs
At 96 hrs
antifungals
Gentamicin Revision
• Gram negative bactericidal agent
• Excellent anti-pseudomonal cover
• Once daily dosing benefits vs tds or bd:
- high peak level – excellent distribution
- post antibiotic effect (>24-36 hours)
- reduced monitoring and administration
- reduced nephro and ototoxicity
- easier monitoring (10-12 hours post dose)
Severe risks of nephrotoxicity and
ototoxicity
• Mrs HR
• 78 years, wt 57kg
• Admitted to outlying hospital acute exacerbation
COPD
• Baseline Cr 80mol/L, Urea 8.5
• Charted gentamicin 160mg daily for 5/7 – no
levels requested
• Baseline CrCl = 45ml/min
Date
3/6
5/6
6/6
7/6
8/6
9/6
10/6
11/6
12/6
13/6
14/6
15/6
16/6
17/6
Gent Dose
160mg
160mg
160mg
160mg
160mg
ceased
Level
Cr
0.08
Urea
8.5
15.5
6.2
9.0
0.11
0.13
0.17
16.9
0.22
28.3
7.8
0.36
0.39
0.41
0.50
0.59
0.65
35.0
21.9
33.6
38.9
40.6
Patient progress
• 15/6 K+ = 6.7, Acidotic to ICU +
haemodialysis
• 21/6 Gent level still 1.4!!!!
• 23/6 complaining of dizziness, unsteady
feeling, vestibular symptoms, vomiting
• 1/7 Cr 0.21 recovering
• 14/11 Out patient – permanent Ototoxicity
Local Sri Lankan Hospital
• 75 yr old patient post amputation, septic
• Gentamicin iv 80mg tds, Co Amoxyclav iv
+ metronidazole iv
• Day 7 reviewed by anesthetists – pain
control
• Noted Urea increased from 7.1 – 15.2
• Patient not septic - ? Need for antibiotic
• Seen Day 12 post operative, Urea = 26
same dose gentamicin
Aminoglycoside dosing and
Monitoring
Case continued…
Day 3:
• Mr AD (67yrs) has now developed sever hospital
acquired pneumonia
• Ward round decisions
- start gentamicin once a day
 dose as per levels each night at 20:00
 recall patient weighs 70 kg
 creatinine has improved (now 140 micro mole/l)
- start Co-Amoxiclav 1.2g IV q8h
Creatinine Clearance
• Recall Cockcroft-Gault Formula:
CrCl (mL/min) = [140-age (years)] * ideal weight (kg)
[0.814 * serum creatinine
(micromol/L)]
{♀ * 0.85 }
If patient 70 kg, 67 y.o. with serum
creat~140micromol/L:
CrCl ≈ 42 mL/min (140-67 X 70) / (0.814 x
140)
Calculating first dose gent
Gentamicin Dose Adjustment
Day 4:
 gentamicin level = 2.5
(taken 08:00, 12 hrs post dose)
• The initial dose given in emergency department was
280mg (4mg/kg x approx 70kg)
Prescribe new gentamicin dose based on level
2.5
Gentamicin Dose Adjustment
• Level at 12 hours = 2.5 (ideal = < 2)
• New Dose =
Level Wanted (mg/L) x Dose Given
(mg)
Level Achieved (mg/L)
In this case: (1.5/2.5) x 280 = 168 mg
• round down to 160 (nearest multiple of 40 mg)
- amps = 40 mg/mL
Adjusting doses of gentamicin
When NOT to take levels
•
•
•
•
Do not take levels if:
Stat dose
Or
Patient has Normal renal function and is
only receiving 1 or 2 doses ie prophylactic
Variable Dose Medication
Drug Level and Time Taken
Dose Time and Actual Time Given
Use in moderate to severe renal
function
• Where ever possible withhold other
nephrotoxic drugs and ensure no other
altenative
• Ie unavoidable use of gentamicin:
• Requires extended dose intervals 36, 48
or 96 hours
• Effectively daily levels wait til < 1.0mmol/l
then dose again
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