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Antibiotics

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  1. Antibiotics Judith Coombes, University of Queensland

  2. 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

  3. 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.

  4. 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

  5. 5 Antibiotics • Benzylpenicillin or Amoxycillin • Streptococcis • Cloxacillin • Staphylococcis • Vancomycin • MRSA • Gentamicin • Pseudomonas • Metronidazole • anaerobes

  6. Skin and Soft Tissue

  7. UTI

  8. Cardiovascular

  9. Respiratory

  10. CNS

  11. 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

  12. Sepsis

  13. 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)

  14. 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

  15. 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

  16. 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

  17. 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

  18. 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)

  19. Calculating first dose gent

  20. 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

  21. 2.5

  22. 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

  23. Adjusting doses of gentamicin

  24. 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

  25. Variable Dose Medication Drug Level and Time Taken Dose Time and Actual Time Given

  26. 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