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 18 June 2018

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Roy Pounder It's mercaptopurine, not 6-mercaptopurine*
Roy Pounder, 07 July 2006

Everybody calls it 6-mercaptopurine, or 6-MP for short, but this is a dangerous error. The approved name for the immunosuppressive in Europe and the USA is mercaptopurine - that is, without the prefix 6-. And the same is true for tioguanine.

So what's the fuss about? Who cares? Well, it's all about safety.

I'll tell you case histories about 2 of my patients:

  • A highly intelligent man of 35 years, an office designer who plans the offices for massive buildings in the centre of London, has Crohn's disease. The time had come for him to start immunosuppression, so I prescribed 6-mercaptopurine 50mg, to be taken every morning. He was dispensed 28 tablets, with the label “6-mercaptopurine 50mg, take one every morning”. He misread the label, and he took 6 tablets every morning - but fortunately came to see me a week later, actually very angry because he'd run out of tablets after 4 days... only 4 left for the last 3 days! I stopped the tablets and he didn't develop toxicity.
  • A woman with Crohn's disease received a similar new prescription, 6-mercaptopurine 50mg, to be taken every morning. She took it to her local pharmacy, and the pharmacist dispensed six 50mg-tablets to be taken every morning. Again, we saw her, as is our routine, 7 days after starting her immunosuppression and I detected the potentially fatal error.

What needs to happen?

Prescriptions must be for mercaptopurine; all writing in terms of hospital notes, doctor's letters, and publications must stop using the 6- prefix; we should stop using 6-MP as our routine abbreviation.

It's all about safety.

This article was first published on on 7 July 2006.

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