Safety of thiopurines in the treatment of inflammatory bowel disease.
BACKGROUND
Thiopurines have proven efficacy in inflammatory bowel disease. However, concerns regarding toxicity have limited the use of these agents as first line of medical therapy.


METHODS
Review of the literature regarding metabolism, efficacy and side effects.


RESULTS
In clinical trials, up to 15% of patients discontinued 6-mercaptopurine or its pro-drug azathioprine prematurely due to adverse events. These events may be divided into dose-independent idiosyncratic reactions and dose-related, pharmacologically explainable toxicity. Dose-independent reactions include skin rash, fever, diarrhoea and pancreatitis. Most frequently observed dose-dependent adverse events are nausea, malaise and myelotoxicity. Furthermore, dose-dependent and dose-independent hepatotoxicity may occur. Recent insights obtained by therapeutic drug monitoring in patients on azathioprine or 6-mercaptopurine have led to strategies to reduce toxicity. One strategy is to detect poor metabolisers of thiopurines by establishing the activity of the key enzyme thiopurine methyltransferase. However, the clinical relevance of this strategy is still a point of debate. Another strategy is to administer 6-thioguanine, which is an agent close to the effective 6-thioguanine nucleotides.


CONCLUSIONS
Therapeutic drug monitoring of thiopurines resulted in strategies to reduce toxicity. The value of these strategies has yet to be proven in prospective randomized trials.
de Jong
D J
DJ
Dept. of Gastroenterology and Hepatology, University Medical Center Nijmegen, Rijnstate Hospital Arnhem, The Netherlands. d.dejong@mdl.umcn.nl
Derijks
L J J
LJ
Naber
A H J
AH
Hooymans
P M
PM
Mulder
C J J
CJ
D001379:Azathioprine / Q000009:adverse effects; D016903:Drug Monitoring / Q000379:methods; D064420:Drug-Related Side Effects and Adverse Reactions / Q000139:chemically induced; D006801:Humans; D007166:Immunosuppressive Agents / Q000009:adverse effects*; D015212:Inflammatory Bowel Diseases / Q000188:drug therapy*; D015122:Mercaptopurine / Q000009:adverse effects*; D016896:Treatment Outcome
D007166:Immunosuppressive Agents; D015122:Mercaptopurine; D001379:Azathioprine