Maternal thiopurine metabolism during pregnancy in inflammatory bowel disease and clearance of thiopurine metabolites and outcomes in exposed neonates

Summary Background Azathioprine and mercaptopurine are considered safe during pregnancy. However, the pharmacokinetic effects of pregnancy on thiopurine metabolism are undefined. Aims To characterise thiopurine metabolism in pregnancy and measure infant metabolite levels and outcomes. Methods Women with IBD who were taking a thiopurine and pregnant or trying to conceive were recruited. Maternal thiopurine metabolites were measured pre‐conception, in each trimester, at delivery and post‐partum. Infant metabolite levels, full blood examination and liver function testing were performed at birth, and repeated until levels undetectable and haematological and biochemical abnormalities resolved. Results Forty patients were included with measurements on at least two occasions, and two with only mother‐baby levels at delivery. The median maternal 6‐TGN level dropped in the second trimester compared with post‐partum (179.0 vs 323.5 pmol/8 × 108 RBCs, P