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 |
|---|---|---|
| Ingredients | 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. |
| Allergy/anaphylaxis | Less common (to povidone, not iodine) |
More common |