Antibiotics

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Antibiotics

• Judith Coombes, University of Queensland

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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

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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.

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MIND ME

• M microbiology guides therapy wherever possible
• I indications should be evidence-based
• N narrowest spectrum required
• D dosage appropriate to the site and type of
  infection
• M minimise duration of therapy
• E ensure monotherapy in most situations

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5 Antibiotics

• Benzylpenicillin or Amoxycillin
• Streptococcis
• Cloxacillin
• Staphylococcis
• Vancomycin
• MRSA
• Gentamicin
• Pseudomonas
• Metronidazole
• anaerobes

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Skin and Soft Tissue
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UTI
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Cardiovascular
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Respiratory
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CNS
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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

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Sepsis
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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 (gt24-36 hours)
• reduced monitoring and administration
• reduced nephro and ototoxicity
• easier monitoring (10-12 hours post dose)

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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

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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

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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

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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 2000
• recall patient weighs 70 kg
• creatinine has improved (now 140 micro mole/l)
• start Co-Amoxiclav 1.2g IV q8h

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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
  creat140micromol/L
• CrCl 42 mL/min (140-67 X 70) / (0.814 x 140)

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Calculating first dose gent
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Gentamicin Dose Adjustment

• Day 4
• gentamicin level 2.5
• (taken 0800, 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

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2.5
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Gentamicin Dose Adjustment

• Level at 12 hours 2.5 (ideal lt 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

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Adjusting doses of gentamicin
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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

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Variable Dose Medication
Drug Level and Time Taken
Dose Time and Actual Time Given
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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 lt 1.0mmol/l
  then dose again

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