The haematological effects of azathioprine
are markedly increased by the concurrent use of allopurinol
is rapidly and extensively metabolised to mercapto- purine. Mercaptopurine is therefore expected to share the interactions of azathioprine
The dosage of azathioprine
or mercaptopurine should be reduced by two-thirds to three-quarters to minimise the risk of toxicity
. Despite taking these precautions toxicity
may still be seen and very close haematological monitoring is advisable if concurrent use is necessary.