TOPIC 5. ANTIBIOTICS AND SULFONAMIDES IN MODERN SURGERY
1. Role in surgery
Antimicrobials are used for treatment of established infection and prophylaxis in selected operations. They do not replace asepsis, adequate perfusion, debridement, drainage or removal of an infected focus.
2. Classification by mechanism
3. Sulfonamides
Sulfonamides are structural analogues of para-aminobenzoic acid (PABA). They competitively inhibit bacterial dihydropteroate synthase, preventing formation of dihydrofolic acid. Trimethoprim inhibits dihydrofolate reductase, producing sequential blockade of bacterial folate metabolism. The combination is often synergistic.
Examples: sulfamethoxazole combined with trimethoprim (co-trimoxazole).
Uses: selected urinary, respiratory, skin/soft tissue and opportunistic infections when the organism is susceptible and the drug is appropriate.
Adverse effects: hypersensitivity reactions, rash including severe cutaneous reactions, photosensitivity, marrow suppression, haemolysis in G6PD deficiency, hyperkalaemia and renal effects.
Precautions: allergy, pregnancy/neonatal considerations, renal function, drug interactions and local resistance patterns.
4. Surgical antibiotic prophylaxis
- Give prophylaxis only when indicated by procedure-specific guidance, wound class, patient factors and expected pathogens.
- Choose an agent active against likely organisms; cefazolin is commonly used for many clean procedures involving skin flora, with alternatives based on allergy and local policy.
- Administer at the correct time before incision so adequate tissue concentrations are present; many agents are given within 60 minutes before incision, while infusion-dependent agents may need earlier initiation.
- Redose during prolonged operations or major blood loss when indicated by drug half-life and protocol.
- Stop prophylaxis according to procedure-specific guidance; prolonged postoperative courses are not routinely justified in the absence of infection.
- Screen for allergy carefully and consider MRSA risk, colonisation and local resistance patterns.
5. Treatment of established surgical infection
- Obtain cultures from appropriate sites when feasible without delaying urgent treatment.
- Start empiric therapy based on severity, likely source, local resistance and patient risk; narrow treatment when microbiology results become available.
- Perform source control: drain abscesses, debride necrotic tissue, relieve obstruction, repair perforation or remove infected devices when indicated.
- Assess renal/hepatic function, allergy, interactions, dose, route and duration; review response and de-escalate when safe.
- Sepsis or septic shock requires immediate resuscitation, urgent antibiotics and prompt source control.
High-yield: Prophylaxis prevents infection in selected operations; therapeutic antibiotics treat established infection. Correct timing, appropriate spectrum, redosing when required and source control are central.