1B - Prophylaxis for a dental procedure
1B) A 70 year old man is going to have his remaining teeth extracted for subsequent dentures. He has mitral valve stenosis. The dentist decides that his medical history warrants prophylactic antibiotic therapy prior to the procedure. Give the name of the antibiotics the man is likely to have been given. What is the mechanism of action of this antibiotic? List at least two common adverse effects. (3 marks)
Speculated mark distribution:
- Naming the antibiotic: 1 mark;
- MOA: 1 mark;
- Two adverse effects: 1 mark
Comment: The number of marks allocated to this question indicates the difficulty level. The majority of pharmacists should be able to score 2 marks.
Answer:
Standard antibiotic prophylaxis for a dental procedure to prevent infective endocarditis (see below) is amoxicillin 2g 30-60 min before procedure (for the answer just ‘amoxillin’ should suffice).
Mode of action: MOA of penicillins is disruption of bacterial cell wall synthesis (inhibition of the bacterial enzymes which manufacture peptidoglycan).
Two common adverse effects:
- Allergic reaction including rash and anaphylaxis
- Diarrhoea/GI upset
CPD:
Mitral valve stenosis is a where for some reason the mitral valve of the heart is abnormal and unable to open fully. This narrows the opening and causes reduced blood flow into the left ventricle which is the main pumping chamber of the heart. The most common cause is rheumatic fever.
Rationale behind antibiotic prophylaxis for dental procedures:
There is a very small theoretical risk of causing infective endocarditis (IE) due to Streptococci in the mouth spreading into the blood stream (bacteraemia) during dental surgery and lodging in the heart. IE is an uncommon but life threatening condition where the endocardium of the heart becomes infected, leading to formation of vegetations on the heart valves. Untreated this leads to heart failure and death. Valve infections are difficult to treat because they are not supplied directly with blood and are unable to be reached by white blood cells.
In the past it was common to prescribe antibiotic prophylaxis for dental procedures, this is now no longer official standard practise due to lack of evidence. Only in a small number of extreme medical conditions may the use of antibiotic prophylaxis may considered reasonable. (Incidentally according to the American Heart Association mitral valve stenosis is not one of these conditions!)
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