Medical Fun Facts Podcast

MFF0073: PANDAS

It’s Monday 03 July 2017.

Tonight’s show is inspired by a friend’s status update on Facebook. My friend is holidaying on a resort in a country which doesn’t regulate drugs in the same way as we do in Australia, the United States, Canada and the UK, you know the like-minded nations.

My friend mentioned she had a sore throat and could buy antibiotics over the counter without a prescription.

I asked what she bought and she replied amoxicillin (Amoxil™).

This raised a few concerns

Most pharyngitis or sore throat is caused by a viral infection. It’s often associated with those viruses that cause head colds. Amoxil is not going to kill viruses. Secondary bacterial infections of the pharynx rarely occur so that’s not a good reason to take Amoxil either.

The Amoxil will be swallowed, absorbed and distributed through the body. Any resident bacteria, especially bowel bacteria will be exposed and through natural selection, susceptible good bacteria will be killed and resistant bacteria will remain. This could potentially, create an imbalance that if other factors are present could lead to colonisation with drug-resistant bacteria. Should the person suffer an injury, say a burn or a significant soft tissue injury of a lower limb, the drug-resistant bacteria may colonise and then infect the wound. This is not a good outcome.

The other problem with Amoxil is that if the sore throat was part of an infectious mononucleosis and the cause is the Epstein-Barr virus, Amoxil commonly results in a rash which sometimes can be quite severe. While this reaction may be allergic-like, it does not result in true allergy. So the problem we face is that a patient may suffer a rash and sometimes that rash can be quite severe. The patient may also come away with the mistaken belief that he or she is allergic to Amoxil and every time he or she needs an antibiotic, he or she may state this with such confidence, that a simple infection that could be treated with Amoxil may be treated with something more potent and more expensive. In some situations, doctors will assume the patient is allergic to all beta-lactam drugs making a whole class of valuable medication unavailable on a misunderstanding.

There’s a basic principle for sore throats. The vast majority are caused by pathogenic viruses for which there are no effective and cheap drugs. The one bacteria we all worry about is Streptococcus pyogenes or the Group A streptococci (GAS for short). There is no way by just looking into someone’s mouth to tell if the cause of the sore throat is Streptococcus pyogenes. The presence or absence of pus is generally meaningless. The only reliable method is to refer the patient for a diagnostic test. This can be culture or any of the newer reliable methods.

The classical treatment in patients who are not allergic to penicillin is penicillin for 10 days. In fact, if we know the cause is definitely group A streptococci, then Amoxil is fine too. The duration is important because the aim is to reduce the opportunity for post-infectious immunological sequelæ like glomerulonephritis and rheumatic fever.

However, it’s not known if antimicrobial therapy will change the incidence of PANDAS or Pædiatric autoimmune neuropsychiatric disorder associated with group A streptococci. PANDAS is an observation that in children with group A streptococcal infection, they may be prone to obsessive-compulsive disorders and tics. That is, T I C S which are spasmodic muscle contractions and not T I C K S the eight-legged blood eating arachnids.

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