Principles of Antibiotics in Surgery

Comprehensive vocabulary flashcards covering the surgical indications, wound classifications, pharmacology, timing, de-escalation, and antimicrobial resistance mechanisms outlined in Dr S.E. Okpara's lecture on Principles of Antibiotics in Surgery.

Antibiotics

Chemical substances that can kill or inhibit bacteria without harm to human hosts, which may be organic (natural) or synthetic.

Bactericidal Antibiotics

Antimicrobial agents that actively kill bacteria, commonly by destroying the bacterial cell wall (e.g., $\beta$-lactams, aminoglycosides, fluoroquinolones, vancomycin, metronidazole).

Bacteriostatic Antibiotics

Antimicrobial agents that inhibit the replication and growth of bacteria, typically by inhibiting protein synthesis (e.g., macrolides, tetracyclines, chloramphenicol, linezolid, clindamycin).

Discovery Void

The historical timeframe between 1987 and 2000 during which no major novel class of antibiotics was discovered and approved.

Contamination

The inoculation of a surgical wound with bacteria, which does not necessarily proceed to infection.

Colonization

The active attachment and multiplication of an inoculated bacterial population within host tissue without overt signs or symptoms of infection.

Infection

The state characterized by the manifestation of clinical signs and symptoms resulting from active microbial invasion and host tissue reaction.

Jawetz Law

Pharmacodynamic principles governing antibiotic combinations: cidal + cidal produces synergism, static + static produces additive effects, and cidal + static produces antagonism.

Synergism

An interaction resulting from an antimicrobial drug combination that yields at least a $4$-fold decrease in the Minimal Inhibitory Concentration ($\text{MIC}$) compared to single agents.

Minimal Inhibitory Concentration (MIC)

The lowest concentration of an antimicrobial substance sufficient to inhibit the visible growth of a bacterium when tested in vitro.

Major Antibacterial Target Sites

The key cellular mechanisms targeted by antibiotics: cell wall synthesis, cell membrane integrity, 30S and 50S ribosomal protein synthesis, nucleic acid synthesis (DNA gyrase and RNA polymerase), and folate pathway synthesis.

Clean Wound (Class I)

An uninfected operative wound without inflammation encountered, where the respiratory, alimentary, and urinary tracts are not entered; associated with an SSI risk of $< 2\%$.

Clean-Contaminated Wound (Class II)

An operative wound where the respiratory, alimentary, or urinary tract is entered under controlled conditions without unusual contamination or major break in asepsis; associated with an SSI risk of $4\text{--}10\%$.

Contaminated Wound (Class III)

An open, fresh accidental wound ($< 4\,\text{h}$), or an operative wound involving a major break in sterile technique, gross gastrointestinal spillage, or acute non-purulent inflammation; associated with an SSI risk of $> 20\%$.

Dirty / Infected Wound (Class IV)

An old traumatic wound with retained devitalized tissue, feces, or pus, or an operation where clinical infection or perforated viscera was present prior to incision; associated with an SSI risk of $> 40\%$.

First-Generation Cephalosporins

Agents including cefazolin and cephalexin with activity primarily against Gram-positive cocci and limited Gram-negatives, serving as gold-standard surgical prophylaxis for clean and clean-contaminated operations.

Fifth-Generation Cephalosporins

Advanced cephalosporins (ceftaroline, ceftolozane-tazobactam) with activity against Methicillin-Resistant Staphylococcus aureus (MRSA) and multidrug-resistant (MDR) Gram-negatives.

Empirical Antibiotic Therapy

Initial antibacterial treatment initiated before specific culture and sensitivity results are available, guided by likely pathogens, site characteristics, and local institutional antibiograms.

Antibiotic De-escalation

The clinical practice of switching from a broad-spectrum empirical intravenous regimen to a narrower, targeted agent based on microbiological culture and sensitivity results reviewed at $48\text{--}72\,\text{h}$.

Intravenous-to-Oral (IV-to-PO) Switch

Transitioning stable patients from parenteral to enteral therapy once they demonstrate clinical improvement, normal bowel absorption, and tolerance of oral intake, typically utilizing agents with high oral bioavailability ($70\text{--}100\%$).

Surgical Antibiotic Prophylaxis

The administration of an antimicrobial agent prior to bacterial contamination in order to reduce the inoculum at the operative site below the threshold required to establish infection.

Surgical Site Infection (SSI)

An infection occurring at or near an operative incision within $30\,\text{days}$ of a surgical procedure, or within $90\,\text{days}$ if foreign prosthetic material was implanted.

Optimal Prophylactic Timing Window

The administration of standard intravenous surgical antibiotic prophylaxis within $0\text{--}60\,\text{minutes}$ prior to surgical skin incision (or $60\text{--}120\,\text{minutes}$ for vancomycin and fluoroquinolones) to ensure adequate tissue levels.

Intra-operative Re-dosing Rule

The administration of an additional prophylactic dose during surgery if the procedure exceeds $2$ elimination half-lives ($2 \times t_{1/2}$) of the drug (e.g., $3\text{--}4\,\text{h}$ for cefazolin) or if blood loss exceeds $\ge 1{,}500\,\text{mL}$.

Mechanisms of Antimicrobial Resistance

The primary physiological pathways bacteria use to survive antimicrobial exposure: enzymatic inactivation, target site modification, active efflux pumps, and reduced membrane permeability.

PBP2a

An altered penicillin-binding protein encoded by the mecA gene that possesses low binding affinity for $\beta$-lactams, mediating methicillin resistance in MRSA.

Persister Cells

A metabolically dormant phenotypic subpopulation of bacteria that survive lethal antibiotic concentrations without genetic changes and contribute to recurrent or chronic infections.

WHO AWaRe Framework

An antibiotic classification tool categorizing agents into Access (first-line, widely available), Watch (higher resistance potential), and Reserve (last-resort agents to be protected from overuse).

Antimicrobial Stewardship Programme (ASP)

A coherent set of multidisciplinary actions and organizational protocols designed to promote the responsible use of antimicrobials to optimize patient outcomes and curb resistance.

Surgical Source Control

Physical surgical interventions—including drainage of abscesses, debridement of infected necrotic tissue, and removal of infected prosthetic implants—that are required to treat surgical infections and cannot be replaced by antibiotics alone.