1. Azathioprine (AZA) Helen Liu Teagan Rolf von den Baumen
PHM Fall 2017
Instructor: Dr. Jeffrey Henderson
Azathioprine (AZA)
Helen Liu
Teagan Rolf von den Baumen
Mishka Danchuk-Lauzon October 3rd 2017

2. General Information Brand name: Imuran
Generic: Apo-Azathioprine, Mylan-Azathioprine, Teva- Azathioprine
Thiopurine – class of immunosuppressive and chemotherapeutic drugs
Immunosuppressant agent
Discovered by George Hitchings and Gertrude Elion in
Nobel prize in physiology or medicine in 1988
Azathioprine is a immunosuppressant agent that is sold as a generic drug and also as a brand name drug under the name Imuran
It was discovered by

3. Recurrent Pericarditis
Uses
Crohn's disease
Lupus nephritis
Uveitis
Multiple sclerosis
Recurrent Pericarditis
Labeled Indications
Renal transplantation
Rheumatoid arthritis
Off label use

4. Administration and Pricing
Oral : usually taken once a day after meals or in divided doses to decrease adverse GI effects
I.V. : usually infused over 30 to 60 minutes but infusion time can be done in 5 minutes up to 8 hours
Dosage
Injection (generic)
100mg (1 injection): $
Imuran Oral
50mg (100 tablets): $
Azathioprine Oral
50mg (100 tablets): $

5. Dosing Dosing depends on the disease being treated
Dosing also varies depending on hepatic impairment, renal impairment and other conditions
Renal transplantation
Following transplantation usually given as 3 mg/kg once daily
Decreased to 1 to 3 mg/kg once daily for maintenance
Not indicated for use in children for renal transplantation (can be taken for off-label use)

6. Pharmacodynamics/Kinetics
Half-life of the drug is approximately 2 hours depending on the patient, it is well absorbed through the oral route
The peak concentration occurs at 1 to 2 hours after oral ingestion
It is primarily excreted through the urine
Approximately 30% of the ingested drug becomes protein bound
The initial drug response occurs in the first 30 to 90 days after beginning drug therapy with the peak response occurring 30 to 120 days after the start of drug therapy

7. Metabolism
Hypoxanthine guanine phosphoribosyltransferase
6-thioguanine-nucleotides
Xanthine oxidase
6-thiouric acid
Thiopurine methyltransferase
6-methylmercaptopurine
Azathioprine is first metabolized in the liver to 6-mercaptopurine via glutathione S-transferase reduction
It is subsequently further metabolized in the liver and the GI tract through 3 main pathways
6-thioguanine metabolites produced during the metabolism of azathioprine mediate the drug’s immunosuppressive and toxic effects

10. hypoxanthine guanine phosphoribosyltransferase (HGPRT),
glutathione transferase
6-thio inosine monophosphate (6-tIMP)

11. inosine monophosphate dehydrogenase (IMPDH)
6-thio inosine monophosphate (6-tIMP)
6-thioxanthylic acid (6-tXMP)

12. Successive phosphorylation by kinases (abbreviated with k)
Guanosine monophosphate synthetase (GMPS) k k
6-thioguanine triphosphate
6-thioguanine monophosphate
6-thioguanine diphosphate
6-thioxanthylic acid (6-tXMP)

13. HGPRT Guanine 6- thioguanine (6-tG)
Alternative pathway to convert 6-tG to 6-tGTP
HGPRT
deoxy-6-thioguanosine 5’ triphosphate (6-tGTP)
Guanine
6- thioguanine (6-tG)
Or 6-thioguanosine

14. 6-tGTP Active metabolite that mimics guanine
6-tGN decreases inflammation.
6-tGN increases T cell apoptosis

15. 6-tGN inhibits many immune and inflammation related genes such as:
tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)
tumor necrosis factor receptor family 7 (TNFRSF7)
α4-integrin

16. 6-tGN incorporation in DNA
6-tGTP nucleotides incorporate itself into the T cell’s DNA
T cell senses DNA damage
Cell cycle is stopped and apoptosis is triggered
T cell proliferation is halted and immature T cells are killed off

17. T cell CD28 Co-Stimulation
T cell maturation relies on costimulation from the TCR and MHC, and CD28 and B7.
Successful costimulation by CD28 inhibits TCR induced apoptosis.
If the T cell does not receive proper costimulation, the CD28 receptor can signal for death (through apoptosis and the death receptor)
One of the enzymes involved with CD28’s signal cascade is Rac1 GTPase.

18. 6-tGN and CD28 Signaling
6-tGTP will bind to Rac1 in the T cell. (Rac1 normally binds to GTP)
Rac1’s pathway is now blocked
CD28’s costimulatory signal to the T cell is converted into an apoptotic signal
Activated T cells are killed off

20. XO Pathway Xanthine oxidase 6-Mercaptopurine Prodrug 6-thiouric acid
Inactive metabolite
Another inactivating metabolic pathway of AZA is the Xanthine oxidase (XO) pathway, which forms oxidized metabolites from 6-Mercaptopurine
6-MP is catabolized by XO to the inactive metabolite 6-thiouric acid (6TU)
6-thiouric acid is then eliminated in the urine
XO is expressed in many tissues, but not in hematopoietic cells (i.e. WBCs), making them more vulnerable to this toxicity

21. Allopurinol X
Allopurinol, a common gout medication is contraindicated in patients taking AZA
Co-prescribing requires significant dose reduction
Allopurinol blocks the XO inactivation pathway of 6MP, leading to accumulation and toxicity

22. Allopurinol + AZA
Cases where pharmacists and health teams who have failed to check drug risks has lead to deaths

23. Genetic Considerations: TPMT polymorphisms and 6-MP toxicity
TPMT (Thiopurine S-methyltransferase) full or parital deficiency is associated with increased IC level of 6-TGNs
An increase in the active metabolite, 6-TGN can cause life-threatening bone marrow suppression when patients are treated with standard doses of 6MP or AZA
The lack of the XO inactivation pathway in hematopoietic cells makes them most vulnerable to toxicity
A deficiency in the TPMT pathway would make both inactivation pathways null, causing an accumulation of active metabolite and suppression of DNA synthesis here
TPMT deficiency associated with increased intracellular levels of 6-thioguanine nucleotides (active metabolite)

24. TPMT Polymorphisms Extensive metabolizers: high enzyme activity
2 WT alleles
Intermediate metabolizers: intermediate enzyme activity
Heterozygotes: 1 variant, 1 WT allele
11% of population
Poor metabolizers: poor or complete lack of enzyme activity
2 variant alleles
Normal dose can be life-threatening or fatal
1/300 individuals
3 phenotypes for TPMT activity: Extensive metabolizers, intermediate metabolizers, and poor metabolizers.
~1/300 individuals in the population are intermediate or poor metabolizers, and for them a ‘normal’ dose can be life threatening
Poor metabolizers require a 10-fold lower dose or alternative drug if possible
The occurrence of severe hematopoietic toxicity is minimized with genetic-based dosing
Results of TPMT phenotyping may not be accurate following recent blood transfusions
Genetic-based dose adjustments aim to equalize levels of IC drug concnetration, therefore preventing toxicity while allowing the drug to still be efficacious

25. Summary Slide
Azathioprine is first metabolized in the liver to 6-mercaptopurine via glutathione S-transferase reduction
Azathioprine is further metabolized in the liver and the GI tract by the following enzymes: hypoxanthine guanine phosphoribosyltransferase, xanthine oxidase and thiopurine methyltransferase
This immunosuppressant is important in preventing rejection of the transplanted organ since it lowers the efficacy of the recipient’s immune system by targeting white blood cells
6-tGN plays many important roles:
1) It inhibits many inflammation related genes
2) it incorporates itself into T cell DNA, halts the cell cycle and triggers apoptosis of immature T cells- stopping t cell proliferation.
3) It further increases apoptosis of T cells by modifying the CD28 costimulatory response into an apoptotic signal. Therefore also deleting activated T cells.
It is important to take into consideration genetic factors when administering this drug since toxicity can occur in patients who have TPMT polymorphisms
Taking Azathioprine and Allopurinol is contraindicated because Allopurinol blocks the XO inactivation pathway of 6MP leading to toxicity

26. References
Wong, D., Derijks, L., Den Dulk, M., Gemmeke, E., & Hooymans, P. (2007). The role of xanthine oxidase in thiopurine metabolism: a case report. Ther Drug Monit, doi: /FTD.0b013e31815bf4dc
Sanderson, J. D. (2015). TPMT Testing Before Starting Azathioprine or Mercaptopurine: Surely Just Do It? Gastroenterology, 149(4), doi: /j.gastro
Wang, L., & Weinshilboum, R. (2006). Thiopurine S-methyltransferase pharmacogenetics: insights, challenges and future directions. Oncogene, 25, doi: /sj.onc
Liew, D., & Booth, J. (2017). Fatal azathioprine toxicity. Aust Prescr, 40(3), doi: /austprescr
Connell, W. R., Kamm, M. A., Ritchie, J. K., & Lennard-Jones, J. E. (1993). Bone marrow toxicity caused by azathioprine in inflammatory bowel disease: 27 years of experience. Gut, 34, doi: /gut
VanLoon, J., Weinshilboum, RM. (1982). Thiopurinemethyltransferase biochemical genetics human lymphocyte activity. BiochemGenet, 20,

27. References 2
Tiede, I., Fritz, G., Strand, S., Poppe, D., Dvorsky, R., Strand, D., … Neurath, M. F. (2003). CD28-dependent Rac1 activation is the molecular target of azathioprine in primary human CD4+ T lymphocytes. Journal of Clinical Investigation, 111(8), 1133–
Dumont, C., Corsoni-Tadrzak, A., Ruf, S., de Boer, J., Williams, A., Turner, M., … Tybulewicz, V. L. J. (2009). Rac GTPases play critical roles in early T-cell development. Blood, 113(17), 3990–
Anna L. Taylor, Christopher J.E. Watson, J. Andrew Bradley, Immunosuppressive agents in solid organ transplantation: Mechanisms of action and therapeutic efficacy, In Critical Reviews in Oncology/Hematology, Volume 56, Issue 1, 2005, Pages 23-46, ISSN , (
Keywords: Immunosuppression; Solid organ transplant
STARZL, T. E., MARCHIORO, T. L., & WADDELL, W. R. (1963). THE REVERSAL OF REJECTION IN HUMAN RENAL HOMOGRAFTS WITH SUBSEQUENT DEVELOPMENT OF HOMOGRAFT TOLERANCE. Surgery, Gynecology & Obstetrics, 117, 385–395.
Elion G.B., Hitchings G.H. (1975) Azathioprine. In: Sartorelli A.C., Johns D.G. (eds) Antineoplastic and Immunosuppressive Agents. Handbuch der experimentellen Pharmakologie / Handbook of Experimental Pharmacology (Heffter-Heubner / New Series), vol 38 / 2. Springer, Berlin, Heidelberg
University of Toronto IMM250 Notes

28. References 3 Azathioprine [PDF]. (n.d.). Ipharmacist.
Booth, R. A. (n.d.). Introduction. Retrieved September, 2017, from
George Hitchings and Gertrude Elion. (2016, September 13). Retrieved September, 2017, from
Physiology or Medicine Press Release. (n.d.). Retrieved September, 2017, from
Images: