2020A Question 02

Compare and contrast povidone iodine and alcoholic chlorhexidine as skin antiseptic agents.

Examiner Report

This question was asking about two commonly used peri-operative antiseptic agents. The domains covered were similar to most previously asked pharmacology questions and covered physicochemistry, action, activity and adverse effects. This paper displayed a lack of knowledge of these two substances in the majority of candidates. A useful reference for this material would be in Katzung “Basic and Clinical Pharmacology” or Stoelting “Pharmacology and Physiology in Anesthetic Practice”.

Model Answer

General Povidone Iodine Alcoholic Chlorhexidine

Polyvinylpyrrolidone (polymer)

Diatomic iodine

10% w/v

Chlorhexidine gluconate (0.5%)

Isopropanol 70%

Mechanism Oxides proteins, nucleotides Both disrupt the cell membrane
Antimicrobial Effect Povidone Iodine Alcoholic Chlorhexidine
Bacteria Yes (G+ > G-) Yes
Viruses Yes (less so) Yes
Fungi Yes Yes
Spores Yes No
Resistance No Yes
Time course Povidone Iodine Alcoholic Chlorhexidine
Onset Slower Faster (alcohol kills quickly)
Duration Long (releases iodine slowly) Long (chlorhex binds epidermis, prevents regrowth)
Inactivation by body fluids Yes (apply to clean skin only) No
Efficacy Povidone Iodine Alcoholic Chlorhexidine
Surgical site Less effective More effective (risk ↓ ~40%)
Vascular access site Less effective More effective (risk ↓ ~50%)
Toxicity Povidone Iodine Alcoholic Chlorhexidine
Brain & neuraxis Less (but max 0.5% skin prep) More
Middle ear Less More
Cornea Less More
Mucous membrane Less More
Abdominal viscera Less More
Other AEs Povidone Iodine Alcoholic Chlorhexidine
Flammability No Yes (alcohol). Must allow to dry.

Less common

(to povidone, not iodine)

More common

Last updated 2021-08-23

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