Alves, Atecla N. L.

Cançado, Eduardo L.

Chocair, Pedro R.

Duley, John A.

Fortini, Alexandre S.

Mendes, Maria E.

Nahas, WIlliam C.

Nasser, Paulo

Ono-Nita, Suzane K.

Pacheco-Neto, Maurílio

Sumita, Nairo M.

Torres, Larissa H. L.

University of Queensland eSpace

RELATO DE CASO
Azathioprine-related severe diarrhea induced by high levels of 
6-thioguanine nucleotides in renal transplant recipient carrying 
mutant thiopurine methyltransferase: a case report
MAURÍLIO PACHECO-NETO1, PAULO D. NASSER2, ATECLA N. L. ALVES1, ALEXANDRE S. FORTINI1, NAIRO M. SUMITA1, MARIA E. MENDES1, 
SUZANE K. ONO-NITA2, EDUARDO L. R. CANÇADO2, LARISSA H. L. TORRES3, JOHN A. DULEY4, WILLIAM C. NAHAS5, PEDRO R. CHOCAIR5
1Hospital das Clínicas, Medical School, Universidade de São Paulo (HC-FMUSP), Central Laboratory Division, Laboratory of Medical Investigation 03, Department of Clinical Pathology, 
FMUSP, SP, Brazil
2 Department of Gastroenterology, FMUSP, SP, Brazil
3 Department of Toxicology, Pharmaceutical Sciences School, Universidade de São Paulo (USP), SP, Brazil 
4School of Pharmacy, University of Queensland, and Mater Medical Research Institute, Brisbane, Australia
5 Renal Transplantation Unit, HC-FMUSP, SP, Brazil 
Correspondence to: 
Pedro R. Chocair
Hospital Alemão Oswaldo Cruz
Diretoria Clínica
Rua João Julião, 331 – Paraíso
CEP: 01323-903
São Paulo, SP, Brazil
Phone/Fax: +55 (11) 3549-0000
3287-8177
diretoriaclinica@haoc.com.br
Conflict of interest: None.
SUMMARY
Introduction: Azathioprine (AZA) is widely used to prevent rejection in organ transplants and treat 
auto-immune diseases. The major side effects reported for the use of AZA are myelotoxicity, hepatotoxic-
ity, and flu-like symptoms, while there are a few reports of severe diarrhea. Thiopurine methyltransferase 
(TPMT) is a major catabolic route that has pharmacogenetic importance. We describe here the evolution 
of a renal transplant recipient carrying a mutant TPMT allele, who developed severe diarrhea related 
to the use of AZA and high levels of 6-TGN. Case presentation: A 28-year-old Brazilian Caucasian 
man underwent preemptive renal transplant in 2006 and presented persistent diarrhea. Therapeutic drug 
monitoring (TDM) of AZA metabolites indicated high levels of red blood cell 6-TGN, and AZA was dis-
continued in view of the patient’s persistent diarrhea. Normalization of bowel habit was gradual, parallel 
to the patient’s physical condition. TPMT genotype showed the mutant allele TPMT*1/*3A, genotype 
associated with low enzymatic activity, high levels of 6-TGN and consequently high susceptibility to side 
effects. Discussion: AZA has been empirically used for about 50 years, even though the pharmacokinet-
ics is demonstrably variable among individuals. It is known that AZA has a higher selectivity for rapidly 
multiplying cells, which also implies higher toxicity. So it can be inferred that the high levels of 6-TGN 
were causing damage to the patient’s intestinal mucosa. This report shows that TDM of AZA may be use-
ful for differential diagnosis of the cause of less frequent adverse events, such as diarrhea.
Keywords: Azathioprine; thioguanine; side effects; diarrhea; drug monitoring; thiopurine methyltrans-
ferase.
©2012 Elsevier Editora Ltda. All rights reserved.
RESUMO
Diarreia severa relacionada à azatioprina induzida por altos níveis de 
nucleotídeos de 6-tioguanina em receptor de transplante renal porta-
dor de gene mutante da tiopurina metiltransferase: relato de caso
Introdução: A azatioprina (AZA) é amplamente utilizada para prevenir a rejeição em transplantes de 
órgãos e no tratamento de doenças autoimunes. A tiopurina metiltransferase (TPMT) é a principal via 
catabólica que apresenta importância farmacogenética. Os principais efeitos adversos relacionados ao 
uso da AZA são mielotoxicidade, hepatotoxicidade e sintomas gripais, apesar de existirem poucos relatos 
de diarreia severa. Descrevemos aqui a evolução de um receptor de transplante renal, portador de um 
alelo mutante da TPMT, que desenvolveu diarreia severa relacionada ao uso de AZA e a altos níveis de 
6-TGN. Apresentação do caso: Paciente do sexo masculino, 28 anos, brasileiro caucasiano, submetido 
a transplante renal preemptivo em 2006 apresentou diarreia persistente. O monitoramento terapêutico 
da AZA indicou níveis elevados 6-TGN eritrocitários e foi interrompido em vista da diarreia. A norma-
lização do hábito intestinal foi gradual, paralelamente às condições físicas do paciente. O genótipo da 
TPMT encontrou o alelo mutante TPMT*1/*3A, genótipo associado à baixa atividade enzimática, níveis 
elevados de 6-TGN e consequentemente alta susceptibilidade a efeitos adversos. Discussão: A AZA tem 
sido utilizada empiricamente por cerca de 50 anos, apesar de sua farmacocinética ser comprovadamente 
variável entre os indivíduos. Sabe-se que esse medicamento apresenta maior seletividade por células de 
multiplicação rápida, o que também implica em maior toxicidade. Assim, podemos inferir que os níveis 
elevados de 6-TGN estavam causando danos à mucosa intestinal do paciente. Este relato mostra que o 
monitoramento terapêutico da AZA pode ser útil para o diagnóstico diferencial das causas menos fre-
quentes de efeitos adversos, como a diarreia.
Unitermos: Azatioprina; tioguanina; efeitos adversos; diarreia; monitoramento terapêutico; tiopurina 
metiltransferase.
©2012 Elsevier Editora Ltda. Todos os direitos reservados.
42
AZATHIOPRINE-RELATED SEVERE DIARRHEA INDUCED BY HIGH LEVELS OF 6-THIOGUANINE NUCLEOTIDES IN RENAL TRANSPLANT RECIPIENT CARRYING MUTANT THIOPURINE METHYLTRANSFERASE: A CASE REPORT
43Rev Assoc Med Bras 2012; 58(Suppl 1):S42-44
INTRODUCTION
Azathioprine (AZA) is a thiopurine drug that is widely 
used to prevent rejection in organ transplants and treat 
auto-immune diseases. The major side effects reported 
for the use of AZA are myelotoxicity, hepatotoxicity, and 
flu-like symptoms. Allergic-type reactions such as pan-
creatitis and rash are less common, while there are a few 
reports of severe diarrhea induced by AZA1-5. Therapeu-
tic drug monitoring (TDM) of thiopurines is achieved 
by measuring erythrocyte levels of the active metabolite 
6-thioguanine nucleotide (6-TGN).
Thiopurine methyltransferase (TPMT) is a major 
catabolic route that has pharmacogenetic importance. Its 
activity is regulated by a gene of about 25 kb (10 exons, 
9 introns) on chromosome 6p22.3. It exhibits codomi-
nant genetic polymorphism and 25 alleles are currently 
described, the most frequent functional (mutant) alleles 
being TPMT*2, TPMT*3A, and TPMT*3C. In general, 
individuals with high TPMT activity have low 6-TGN 
levels and poor clinical outcome, while patients with low 
TPMT activity have 6-TGN levels above therapeutic lev-
els and are more susceptible to side effects.
We describe here the evolution of a renal transplant 
recipient carrying a mutant TPMT allele who developed 
severe diarrhea related to the use of AZA and high lev-
els of 6-TGN. To our knowledge, this is the first report 
of diarrhea related to TPMT mutation and high levels of 
6-TGN.
CASE PRESENTATION
A 28-year-old Brazilian Caucasian man underwent pre-
emptive renal transplantation in 2006, followed by main-
tenance immunosuppressive regimen initially consisting 
of mycophenolate, tacrolimus and prednisone. In July 
2008, AZA was started (150 mg, 2 mg/kg daily) in place 
of mycophenolate due to persistent diarrhea, followed by 
only transient improvement of this side effect. Parasito-
logical tests were negative and colonoscopy ruled out in-
testinal structural damage.
The TDM of AZA indicated high levels of red blood 
cell 6-TGN: 1,536 ρmol/8x108 red blood cells (RBC) on 
the occasion of the first assay in November 2008. The 
AZA dose was reduced to 125 mg/day, and in July 2009 a 
second assay indicated a 6-TGN level of 2,137 ρmol/8x108 
RBC. Two weeks later, AZA was discontinued in view of 
the patient’s persistent diarrhea. After a further six days 
6-TGN level had dropped to 1,122 ρmol/8x108 RBC, with 
a progressive decrease until undetectable levels were 
achieved at about 40 days after medication withdrawal 
(Figure 1). Normalization of bowel habit was gradual, 
parallel to the patient’s physical condition, becoming 
normal four to five weeks after AZA withdrawal. Nine 
months later, while undergoing a maintenance immuno-
suppressive regimen consisting of 4 mg prednisone and 5 
mg tacrolimus, the patient had stable renal function with 
creatinine around 1.2 mg/dL, and had recovered 19 kg 
in weight.
Figure 1 – Patient weight changes over 3 years, also showing 6-TGN levels (pmol/8 x 108 RBC).
AZA
initiation
1,536
28
-A
ug
-2
00
7
30
-O
ct-
20
07
15
-Ja
n-
20
08
2,137
1,122
W
ei
gh
t 
(k
g) AZA
interruption
85
80
75
70
65
60
55
Weight
6-TGN (pmol/8 x 108 RBC)
217 < 60
15
-A
pr
-2
00
8
24
-Ju
n-
20
08
4-
No
v-2
00
8
3-
Fe
b-
20
09
16
-A
pr
-2
00
9
28
-Ju
l-2
00
9
11
-A
ug
-2
00
9
14
-S
ep
-2
00
9
15
-S
ep
-2
00
9
27
-O
ct-
20
09
22
-D
ec
-2
00
9
5-
Ma
r-2
01
0
13
-A
pr
-2
01
0
1-
Ju
n-
20
10
MAURÍLIO PACHECO-NETO ET AL.
44 Rev Assoc Med Bras 2012; 58(Suppl 1):S42-44
TPMT genotype determined by sequencing showed 
the patient carried the mutant allele TPMT*3A, a geno-
type associated with low enzymatic activity, high levels of 
6-TGN and consequently high susceptibility to side effects.
DISCUSSION
AZA has been used for about 50 years, but its mechanism 
of action is still poorly understood. It continues to be used 
empirically, i.e. mg/kg, even though the pharmacokinetics 
is demonstrably variable among individuals, without any 
correlation with body weight. The case described herein 
reports a patient who was withdrawn from mycophenolate 
because of diarrhea and then started on a standard AZA 
dose. He then developed high levels of 6-TGN and severe 
diarrhea. After extensive investigation, laboratory tests 
and imaging assessment, the only cause of the continuing 
diarrhea appeared to be the high levels of 6-TGN.
This finding may be relevant also for patients with in-
flammatory bowel diseases, as the disease may cause sensi-
tization of the gut and diarrhea. It is known that AZA has 
a higher selectivity for rapidly multiplying cells, such as 
neoplastic cells, leukocytes and mucosal cells. This higher 
selectivity also implies higher toxicity to these cells. So it 
can be inferred that the high levels of 6-TGN were caus-
ing damage to the patient’s intestinal mucosa, followed 
by malabsorption, diarrhea and weight loss. The delay of 
about 30 days until cessation of diarrhea corresponded to 
the period reported as necessary for the recovery of intes-
tinal villi1.
This report shows that TDM of AZA, such as RBC 
6-TGN, may be useful for differential diagnosis of the 
cause of less frequent adverse events, such as diarrhea and 
other toxicity effects related to drug use.
ACKNOWLEDGMENTS
This study was presented in part to the III International 
Thiopurine Symposium, held at the Instituto de Educação 
e Ciências, Hospital Alemão Oswaldo Cruz, São Paulo, 
September 30th – October 2nd, 2010.
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1. Ziegler TR, Fernández-Estívariz C, Gu LH, Fried MW, Leader LM. 
Severe villus atrophy and chronic malabsorption induced by azathio-
prine. Gastroenterol.  2003;124:1950-1957.
2. Santiago M, Fuller R, Alarcon-Segovia D. Diarrhea secondary to aza-
thioprine in two patients with SLE. Lupus. 1999;8:565.
3. Assini JF, Hamilton R, Strosberg JM. Adverse reactions to azathio-
prine mimicking gastroenteritis. J Rheumatol. 1986;13:1117-1118.
4. Marbet U, Schmidt I. Severe life-threatening diarrhea caused by aza-
thioprine but not by 6-mercaptopurine. Digestion. 2001;63:139-142.
5. Daneshmend TK, Hawkey CJ, Logan RF, Walt RP. Devastating diar-
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Azathioprine-related severe diarrhea induced by high levels of 6-thioguanine nucleotides in renal transplant recipient carrying mutant thiopurine methyltransferase: A case report

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Azathioprine-related severe diarrhea induced by high levels of 6-thioguanine nucleotides in renal transplant recipient carrying mutant thiopurine methyltransferase: A case report

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