The British journal of dermatology, Volume 173, Issue 5, 13 2 2015, Pages 1338-1339 Increased liver enzyme levels during azathioprine treatment: beware of concomitant use of proton pump inhibitors. van der Schaft J, van Schaik RH, van den Broek MP, Bruijnzeel-Koomen CA, de Bruin-Weller MS