2. OUTLINE
Definitions
Classification of Antibiotics
Use of antibiotics in surgery
- Prophylactic
- Therapeutic
Classification of Surgical Wounds
Causes and Prevention of Wound Infection
Indiscriminate Use of Antibiotics
Toxicity of Antibiotics
3. DEFINITIONS
An antibiotic is a substance that has the
ability to kill or inhibit the growth or spread of
a micro-organism.
Antibiotics are products of various species of
fungi that suppress growth or kill other micro-
organisms
4. Def cont
• Antibacterial-is any substance that destroys bacteria or
suppresses their growth.
• Antimicrobial-is a general term for synthetic agents
like drugs, chemicals or other substances that either kill
or slow the growth of microorganisms.
-It can be antibacterial drugs , antiviral agents ,
antifungal agents or antiparasitic agents.
5. Antibiotic Classification
a)mechanism of action
1.Cell wall synthesis inhibitors(inhibit
Peptidoglycan synthesis)
B-lactams-penicillins, cephalosporins,
carbapenems
Others-vancomycin, bacitracin
2. Protein synthesis inhibitors (interfere with 50s or
30s of rRNA)
Tetracyclines, aminoglycosides, macrolides,
Chloramphenicol,clindamycin
3. Folate antagonists(Sulphonamides)
Inhibit folate synthesis or reduction
e.g sulfamethoxazole, trimethoprim
4.Quinolones
DNA gyrase inhibitors
e.g levofloxacin, ciprofloxacin
5. Nitroimidazole e.g metronidazole
6. RNA polymerase inhibitor e.g Rifampicin
6.
7. Classif Contd;
b)Mode of Action
•Bactericidal: Kill the micro-organism
•Bacteriostatic: Retard the growth/spread of the organism
Bacteriostatic Bactericidal
Chloramphenicol Penicillins
tetracyclines Aminoglycosides
macrolides Cephalosporins
Sulfonamide Quinolones
clindamycin Metronidazole
8. Classifi Cont;
c) Based on Spectrum of Activity
- Narrow spectrum
- Extended spectrum
- Broad spectrum
9. Selection of antibiotics
• Requires knowledge of
-The organism involved and its sensitivity to a particular agent.
-The site of infection(CNS, bone, GIT, GUT)
-The safety of the agent.
-Patient factors e.g age, pregnancy, systemic illnesses,
hypersensitivity
-Availability, accessibility, affordability of the drug
10. NORMAL FLORA IN A NORMAL PERSON
IN THE COMMUNITY
ANATOMICAL SITE NORMAL FLORA
SKIN Staphylococcus, streptococcus,
propionibacteria
ORAL CAVITY ABOVE +, anaerobes (Actinomyces,
Bacteroides, Peptostreptococcus,
Fusobacterium, lactobacillus,
propionibacterium) & gram –ve rods
NASOPHARYNX Staph., strep., H. influenza & anaerobes
THORAX Staph, strep., & propionibacteria
GIT Flora of the nasopharynx+
enterobacteriaceae, Lactobacillus, candida
sp
URINARY TRACT Normally sterile
FEMALE GENITAL TRACT Lactobacillus sp.,strep. agalactiae
LIMBS Staph., strep., propionibacteria
11. A PERSON IN A HOSPITAL/ LONG-
TERM CARE FACILITY
UPPER
RESPIRATORY
TRACT
staph sp., anaerobes, Enterobacteriaceae (E. coli, klebsiella),
candida sp., pseudomonas sp.
SKIN Staph sp., Enterobacteriaceae
GIT Anaerobes , enterococcus sp( E. faecalis, E. faecium),
enterobacteriaceae( E. coli, klebsiella, salmonella, shigella),
candida sp., pseudomonas
GENITAL TRACT Candida species
12. ANTIBIOTICS FOR SURGICAL
PROPHYLAXIS
Surgical antibiotic prophylaxis is defined as the use of antibiotics to
prevent anticipated infection at the surgical site.
Indications for prophylaxis
contaminated (risk of infection is 15%)and clean-contaminated (risk of
infection is 6%) wounds
Clean wound in which implants or prosthesis are inserted
Animal or human bite
Open fracture
13. Delay to cleaning >6 hrs
Foot/hand wounds
Wound length >5cm
Crush injuries
Wound involving body cavity/perineum
Immunosuppressed pts
Burns
NOTE: In our set up, every patient going to theatre has to be given prophylactic
antibiotics because of the high risk of infections/ bacterial contamination prior to
surgery.
14. Principles of Antibiotics Prophylaxis in
Surgery
1. Timing- within 30 min-1 hr of making incision; often during
induction of anesthesia- so that adequate blood and tissue levels are
present at the time skin incision is made.
Timing is dependent on the half life of the antibiotic used; most of the
times it falls within the above range.
2.Mechanism/Mode of action- bactericidal preferred over bacteriostatic.
3. Spectrum- The antibiotic selected should only cover the likely
pathogens- narrowest antibacterial spectrum required
15. Principles of Prophylaxis Continued
4.Route- IV because of the need for fast onset
5.Duration- once STAT dose. Repeat dose once if
surgery takes longer than 4 hrs, when there is
contamination during operation or when there is
more than 1.5 L of blood loss.
6. Dosage- should be high dose( maximum dose)
16. Goals of Antibiotic Prophylaxis
1.Reduce the incidence of surgical site infections
2.Minimize the effect on the patient’s normal bacterial flora
3.Minimize adverse effects of antibiotics
4.Minimize the emergence of antibiotics resistant strains of
bacteria
PLEASE NOTE
• Antibiotic prophylaxis is not a substitute of aseptic technique.
17. GUIDELINES FOR SURGICAL
PROPHYLACTIC ANTIBIOTIC
PROCEDURE SUGGESTED ANTIBIOTIC
GI SURGERY IV ceftriaxone 1g + iv metronidazole
500mg
HERNIA REPAIR, BREAST(major excision),
BURNS
IV Cloxacillin 1g
VASCULAR OPERATION IV Ampicillin/ sulbactam 1.5 g
NEUROSURGERY IV Ceftriaxone 1g + iv metronidazole
500mg
UROLOGY IV amoxicillin/ clavulanate 1.2 g
19. Principles Of Therapeutic Antibiotic Use
1. Establish a clinical diagnosis and the need for antibiotic use based on hx and physical
examination
2. Determine the urgency of the situation
- non- urgent: mild infection or chronic infection
- Urgent situation: suspected severe infection
3.Obtain appropriate clinical specimens for examination, culture and sensitivity
4. Remove barrier to cure thru
-debridement
-Incision & drainage
-Good wound care
20. 5. Determine the most likely organism causing infection
-focus of infection – age
- epidemiologic features -prior culture data
6. Choose the best agent available to treat the pathogen.
7. Antibiotic combination can be considered to achieve synergism
8. Assess effectiveness of antibiotic therapy
-decrease in temp within 48 hrs after adm of antibiotics
-decrease in inflammatory markers like CRP( 25% from baseline)
within 24 hrs
9.Initial therapy may need to be modified after culture results.
21. Empirical Antibiotic Therapy
• Initiation of treatment before isolation of an organism.
• Empirical antibiotic use is mostly based on the doctor’s experience.
• When to start:
– When risk of surgical infection is high- based on underlying disease
process. (e.g. Perforated appendicitis).
– Significant contamination during surgery has occurred. e.g.
considerable spillage of colon contents
– In critically ill patients when potential site for infections has been
identified
– Severe sepsis or septic shock
• Usually is a short course (3-5 days)
• Stop if presence of a local site infection or systemic infection is not
identified.
22. Indications for empirical therapy
• Suspected or diagnosed infectious etiology
e.g. UTI, pneumonia, cellulitis
• Neutropenia or other immunocompromised
states
• Asplenia- due to the potential of
overwhelming post splenectomy infections
23. Indications for empirical therapy
Con’t
Abdominal trauma- 3rd gen cephalosporin(
ceftriaxone…)
Perforated viscus, peritonitis – 3rd gen
cephalosporins & flagyl
Breast abscess (S.aureus)- cloxacillin
Mycotic pseudo aneurysm- cloxacillin
Prosthetic graft infection-3rd generation cephalosporin
24. Duration of therapy
• Should be long enough to prevent relapse yet not excessive as can increase side
effects and resistance
• Antibiotic use post-operatively normally takes 3-5 days. It is based on the
likelihood of infections after surgery.
• Factors such as decreasing WBC and lack of fever guide therapy
• For instance:
-Penetrating GI trauma without extensive contamination (12-24 hours)
-Perforated/gangrenous appendicitis (3-5 days)
-Peritoneal soilage due to perforated viscus with moderate degree of contamination
(5-7 days)
-Extensive peritoneal soilage/ immunocompromised host (7-14 days)
25. CLASSIFICATION OF SURGICAL
WOUNDS
1.CLEAN WOUND ( <5% infection rate)
-wound made under ideal operating condition
-No entry into hollow viscus i.e the oropharyngeal cavity, lumen of the respiratory, alimentary or
genitourinary tract.
-Inflammation is not encountered
-No break in sterile technique occurs
-Example: hernia repair, breast biopsy, thyroidectomy
2. CLEAN-CONTAMINATED .(2-8% Infxn rate)
-Hollow viscous entered without significant spillage
-no inflammation
-minor breaks in the aseptic technique
–Example: appendectomy, biliary tract
26. 3.CONTAMINATED WOUND (15-20% infxn rate)
- includes open, fresh and traumatic wounds
-uncontrolled spillage from viscous
-operations with major breaks in the aseptic technique
- incisions encountering acute, non purulent inflammation e.g in cholecystitis or cystitis
-other examples: penetrating abd trauma, enterotomy during bowel obstruction, large tissue injuries
4. DIRTY WOUND( 30-40% infxn rate)
-Traumatic wounds ( >4 hrs old)
-untreated uncontrolled spillage
-severe inflammation
-perforated viscera or operations involving clinically evident infxns e.g pus in the wound
-wounds containing foreign bodies or devitalized tissue.
27. CAUSES OF WOUND INFECTION
• Combination of bacterial numbers and virulence that overcome local host
defenses.
• Bacterial factors:-
– Type of bacteria
– Numbers of inoculums ≥105.
– Toxins produced by pathogen
– Organism ability to resist phagocytosis and intra-cellular destruction
28. CAUSES OF WOUND INFECTION
cont
• Local wound factors:-
– Inhibition of local defense mechanisms
– Presence of foreign bodies
– Strangulation of tissues
– Presence of dead tissue, haematomas or seromas
29. CAUSES OF WOUND INFECTION cont.
Patient Factors:
• Very young and very old
• Reduced blood flow to wound – vascular disease, anemia
• Inhibition of cellular function – malignancy states, trauma
• Immunocompromised states
30. PREVENTION OF WOUND INFECTION
• Avoidance of bacterial contamination- aseptic technique
• Environmental factors: theatre design to limit airborne
contamination. Use of ultraviolet light for decontamination of
theatre, lamina flow of ventilation systems, limiting of traffic
within operating room.
• Sterilization techniques
31. Prevention of Wound Infection: Pre-
operative preparation of patient
• Pre-op shower using antibacterial soap- for elective cases
• Treatment of all cutaneous and any other infection before elective
procedures
• Hair removal – extensive hair removal should not be done. If needed (e.g
to prevent adherence of dressings), it should be done on the operating table
because minor skin injury enhances superficial bacterial colonisation.
• Skin preparation–adequate cleaning (5-7 min) using
chlorhexidine/povidine-iodine and draping (antimicrobial incision drape)
are vital.
32. Operating room team and discipline-
prevention of wound infections
• Wear clean scrub suits, cap and mask.
• Scrub hands and forearms with antimicrobial
soap
• Careful wearing of gowns and gloves
• Change punctured or torn gloves
33. Dangers of Indiscriminate Use of
Antibiotics
Changes of normal flora of body --> overgrowth of
resistant organisms with development of drug
resistance
- Masking serious infection without eradicating it (e.g.
abscess)
- Direct Drug Toxicity
- Alteration of individual and hospital bacterial ecology
- Higher cost of treatment
- False sense of security
34. Antibiotic resistance
Resistance of a micro-organism to an antimicrobial agent to which it was
previously sensitive.
Intrinsic – drug target is not present in the bacteria’s metabolic pathways
Acquired- mutation, transfer of genetic material from the resistant to
susceptible organisms (plasmids, transposons, bacteriophages)
Factors contributing to resistance
Excess antibiotic use(over a long period)
Incorrect use of broad spectrum agents
Incorrect dosing
Non compliance
