Delayed leukopenia following intentional azathioprine ingestion

ABSTRACT

Background: Azathioprine is a purine analog metabolized to 6- mercaptopurine (6-MP) utilizing glutathione. Its high oral bioavailability and longer duration of action make it viable as a treatment for ulcerative colitis or as an anti-rejection medication for renal transplant patients. Specific experience in overdose with this agent is limited although toxicity mimics 6-MP including hepatotoxicity, delayed leukopenia, and acute interstitial nephritis. Case report A 46 year old female (64 kg) with a history of ulcerative colitis, migraines, and anxiety presented with a selfreported intentional ingestion of 1000mg azathioprine and presented to care approximately 8 h post-ingestion. Her compliance with azathioprine preceding the ingestion was unclear. She reported taking her other medications as prescribed (tadalafil, sulfasalazine, fioricet, alprazolam) the day prior to presentation. Other than one episode of emesis without pill fragments, myalgias, headache she had no other symptoms. Her presenting vital signs were HR 84, RR 22, BP 90/63, T 36.2 degreeC. Initial labs included a normal chemistry profile, undetectable serum acetaminophen and salicylates, an ethanol level of 50 mg/dL and venous lactate of 1.6mmol/L. She received a total of 3 L of crystalloid IV fluids with improvement in blood pressure to 125/66 and was transferred for higher level of care. Due to the delay in presentation and well appearance, activated charcoal and hemodialysis were considered but deferred. While inpatient she had laboratory evaluation including CBC and differential every 8 h. In the ED she developed a fever, 38.1 degreeC. PCR testing for COVID-19 was negative. Whole blood thiopurine metabolites (Prometheus Biosciences, Test 3200) were sent approximately 33 h from time of ingestion. 6-thioguanine levels were 108 pmol/8x10degree8 RBC, below the therapeutic reference range (230-400 pmol/8x10degree8 RBC). 6-methylmercaptopurine metabolites were below the lower limit of quantification (761pmol/8x10degree8 RBC). Genetic testing for thiopurine S-methyltransferase was declined by the patient. She was hospitalized for 4 days and did not develop any substantial vital sign abnormalities or creatinine elevation. Her absolute neutrophil count dropped to 500/mm3 approximately 76 h post-ingestion, but started to improve 84 h post-ingestion and granulocyte-macrophage colony-stimulating factor was deferred. Her peak AST was 113 IU/L, approximately 46 h post-ingestion and returned to normal (16 IU/L) upon follow-up 7 days postingestion. White blood cell count 7 days post-ingestion was 4.3 K/mm3. Discussion(s) Azathioprine overdose is rarely reported in the literature. Case reports describe delayed leukopenia and hepatotoxicity from repeat supratherapeutic ingestions, however, based upon limited experience serious toxicity from single acute ingestions appears rare. A report of a single acute ingestion of 7500mg of azathioprine resulted in moderate leukopenia (4.1 K/ mm3) 3 days post-ingestion. Peak immunosuppressive effects can take up to 2 weeks from initiation or change in dose. Symptoms in this case are consistent with effects from azathioprine including vomiting, transient hypotension, and myalgias. Conclusion(s) Intentional ingestions of azathioprine are infrequently reported and can result in serious delayed myelosuppression. We report a case of a single acute ingestion of >15 mg/kg resulting in delayed myelosuppression managed conservatively.