Severe megaloblastic anaemia associated with abnormal azathioprine metabolism

Br J Clin Pharmacol. 1984 Feb;17(2):171-2. doi: 10.1111/j.1365-2125.1984.tb02333.x.


Severe anaemia is a rare, unexplained, side effect of azathioprine therapy. We report here such a case associated with a previously unreported abnormality in azathioprine metabolism. A 57 year old man on azathioprine therapy, for a presumed collagen vascular disease, developed severe megaloblastic anaemia. This resolved on cessation of azathioprine treatment. A very high concentration of an azathioprine metabolite, 6-thioguanine nucleotide, was found in the patient's red blood cells and this was confirmed by subsequent rechallenge with a single dose of 50 mg azathioprine.

Publication types

  • Case Reports
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Anemia, Macrocytic / chemically induced*
  • Anemia, Megaloblastic / chemically induced*
  • Azathioprine / adverse effects*
  • Guanine Nucleotides / blood
  • Humans
  • Male
  • Middle Aged
  • Thionucleotides / blood


  • Guanine Nucleotides
  • Thionucleotides
  • 6-thioguanylic acid
  • Azathioprine