Literature regarding acute human toxicity of thiopurines is limited to a handful of case reports. Our objectives were to
describe all cases of overdose with thiopurines reported to the Swiss Toxicological Information Centre between 1995–2013.
A retrospective analysis was performed to determine circumstances, magnitude, management and outcome of overdose
with these substances. A total of 40 cases (14 paediatric) were reported (azathioprine, n = 35; 6-mercaptopurine, n = 5). Of
these, 25 were with suicidal intent, 12 were accidental and 3 were iatrogenic errors. The magnitude of overdose ranged
from 1.5 to 43 (median 8) times the usual dose in adults. Twelve cases (30%) had attributable symptoms. The majority of
these were minor and included gastrointestinal complaints and liver function test and blood count abnormalities.
Symptoms were experienced by patients who took at least 1.5-times their usual daily thiopurine dose. Overdoses over two
or more consecutive days, even if of modest size, were less well tolerated. One case of azathioprine and allopurinol coingestion
over consecutive days led to agranulocytosis. Decontamination measures were undertaken in 11 cases (10
activated charcoal, 1 gastric lavage) and these developed fewer symptoms than untreated patients. This study shows that
acute overdoses with thiopurines have a favourable outcome in the majority of cases and provides preliminary evidence
that gastrointestinal decontamination with activated charcoal may reduce symptom development after overdose of these
substances if patients present to medical services soon after ingestion.