Clopidogrel and TIA - Is it Always Effective?
Does clopidogrel help to prevent strokes in everyone?
Genetic tests have come a long way.
From cancer to inherited diseases, the advancement of research and technology in the 21st century can track even the smallest variations in genes.
Every so often I have patients who come to me asking about certain genetic tests. The most recent was haemochromatosis and I had to desperately search google, NICE and other webpages to get some clarity. Turns out we don’t offer genetic testing and offer blood tests instead.
NICE have recently produced guidance on a new form of genetic test - this time for TIA/strokes. For a long time we’ve relied on clopidogrel - also known as “clopi” to give patients the protection they need once they’ve had a confirmed TIA. The consensus seems to now be that clopidogrel doesn’t work on everyone. This is a game changer.
It all centres around a particular enzyme - CYP2C19. The current thinking is that 32% of people in the UK, particularly those from an Asian background have a deficiency in the enzyme. The enzyme comes from a family of enzymes that I’m sure you’re familiar with - cytochrome p450 (CP450).
Yes, it’s that bugger again. CP450 is responsible for metabolising cholesterol, steroids and other lipid based tablets. It’s a real pain as I’m sure you know as some medications enhance cp450 activity and others hinder it so as clinicians we tend to be quite cautious. Some patients have deficiencies in “para-chains” of cp450 such as CYP2C19.
This means that those with the deficiency are unable to convert clopidogrel into its active form. Current evidence suggests that these patients have a 46% additional risk of having a stroke post TIA. Currently there are no genetic variation tests available on the NHS but this will most likely change in the future. There are other alternatives to clopidogrel but before proposing them NICE is currently working out the best way forward.
The plan is to keep patients on clopidogrel whilst ensuring that we refer early to stroke services as well as keeping an eye on other causative factors including diabetes and hypertension. This is certainly an interesting space to watch.
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