thioguanine-anhydrous and Drug-Hypersensitivity

Azathioprine and mercaptopurine are widely used in the treatment of inflammatory bowel disease. However, its use is limited by adverse drug event related to the relatively narrow therapeutic index of the active metabolites. Several patients discontinue treatment because of intolerable adverse events or toxicity such as leucopenia and hepatotoxicity. High 6-thioguanine nucleotides and 6-methylmercaptopurine ribonucleotides levels are associated with toxicity. Variations in the thiopurine S-methyltransferase (TPMT) gene can lead to diminished TPMT enzyme activity and to an increased incidence of myelotoxicity due to high 6-methylmercaptopurine ribonucleotides levels after treatment with azathioprine and mercaptopurine. Unlike azathioprine and mercaptopurine, thioguanine is more directly metabolized to the active metabolites without formation of the toxic 6-methylmercaptopurine ribonucleotides. Taking this into account, it seems likely that thioguanine is less associated with myelotoxicity due to TPMT deficiency. However, we report the case of a Crohn's disease patient with life-threatening complications on 6TG treatment due to TPMT deficiency. Our patient developed a severe pancytopenia on thioguanine therapy, with 6-thioguanine nucleotides levels more than 10 times higher than the upper limit of the therapeutic window and was found to be a TPMT poor metabolizer (TPMT *3A/*3A). This case strongly illustrates that knowledge of TPMT enzyme activity is very important in the use of all thiopurines, including thioguanine. In conclusion, clinicians should be aware of the impact of TPMT deficiency on the metabolism of thioguanine and should consider performing preemptive TPMT genotyping in combination with frequent blood test monitoring when using thiopurines in general.

Topics: Aspergillosis; Drug Hypersensitivity; Female; Humans; Inflammatory Bowel Diseases; Middle Aged; Pancytopenia; Purine-Pyrimidine Metabolism, Inborn Errors; Severity of Illness Index; Thioguanine

The activity of the enzyme thiopurine methyltransferase (TPMT) is regulated by a common genetic polymorphism. One in 300 individuals lack enzyme activity and 11% are heterozygous for a variant low activity allele and have an intermediate activity. The thiopurine drugs azathioprine, mercaptopurine and thioguanine are substrates for TPMT; these drugs exhibit well documented myelosuppressive effects on haematopoietic cells and have a track record of idiosyncratic drug reactions. The development of severe bone marrow toxicity, in patients taking standard doses of thiopurine drugs, is associated with TPMT deficiency whilst the TPMT heterozygote is at an increased risk of developing myelosuppression. Factors influencing TPMT enzyme activity, as measured in the surrogate red blood cell, are discussed in this review to enable an appreciation of why concordance between TPMT genotype and phenotype is not 100%. This is particularly important for lower/intermediate TPMT activities to avoid misclassification of TPMT status. TPMT testing is now widely available in routine service laboratories. The British National Formulary suggests TPMT testing before starting thiopurine drugs. Dermatologists were quick to adopt routine TPMT testing whilst gastroenterologists do not specifically recommend TPMT screening. TPMT testing is mandatory prior to the use of mercaptopurine in childhood leukaemia. Thiopurine drug dose and other treatment related influences on cell counts explain some of the differing recommendations between clinical specialities. TPMT testing is cost-effective and the major role is in the identification of the TPMT deficient individual prior to the start of thiopurine drugs.

Topics: Antimetabolites, Antineoplastic; Azathioprine; Cost-Benefit Analysis; Drug Hypersensitivity; Drug Labeling; Genetic Testing; Genotype; Humans; Mercaptopurine; Methyltransferases; Phenotype; Purine-Pyrimidine Metabolism, Inborn Errors; Thioguanine

Thiopurine compounds are commonly used in the treatment of childhood acute lymphoblastic leukemia, and as immunosuppressants following organ transplantation or for treatment of various autoimmune disorders. Thiopurine S-methyltransferase (TPMT) is required for detoxification, through S-methylation, of 6-thioguanine nucleotides (TGNs), a byproduct of thiopurine metabolism. Single nucleotide polymorphisms (SNPs) in the TPMT gene have been shown to affect its function, with some variants associated with serious clinical manifestations including severe to fatal myelosuppression and organ transplant rejection following treatment with standard thiopurine doses. In this study, we describe a TaqMan real time PCR allelic discrimination assay requiring minimal DNA input for TPMT genotyping.. We designed controls for the homozygous wild type and allelic variants of TPMT*2, *3B, and *3C. Genomic DNA was extracted from an additional 412 human blood samples. The samples were tested for the TPMT*2, *3B, *3C, and *3A polymorphisms by TaqMan genotyping assays using the AB 7500 FAST Real-Time PCR instrument. Allelic discrimination plots were used to identify each mutation.. The TaqMan assay correctly genotyped all custom control DNA samples. Of the 412 tested samples, our assay identified 375 samples as wild-type *1/*1 (91.02%), 3 as *1/*2 (0.73%), 1 as *1/*3B (0.24%), 3 as *1/*3C (0.73%), 27 presumed to be *1/*3A (6.55%), and 3 as *3B/*3A (0.73%).. The clinical implications of TPMT genotyping, along with the simplicity and specificity of the TaqMan genotyping assays make this test highly suitable for use in a clinical laboratory.

Topics: Drug Hypersensitivity; Genotype; Genotyping Techniques; Humans; Methyltransferases; Mutation; Polymorphism, Single Nucleotide; Precursor Cell Lymphoblastic Leukemia-Lymphoma; Purine-Pyrimidine Metabolism, Inborn Errors; Thioguanine

Thiopurine S-methyltransferase (TPMT) is an excellent example of an enzyme whose pharmacogenetic polymorphisms affect efficacy and toxicity of a drug. The association between TPMT activity and thiopurine-related myelosuppression is well recognized. To study the significance of TPMT deficiency in thiopurine metabolism and immunosuppressive activity in vitro, we established RNA interference-based TPMT knockdown (kd) in a Jurkat cell line.. In Jurkat TPMT kd cells, TPMT expression was reduced to 73% at the RNA level and 83% at the protein level. TPMT kd cells were more sensitive to 6-mercaptopurine (6-MP) (10 μmol/L) and 6-thioguanine (6-TG) (8 μmol/L) than wild-type (wt) cells, (32% versus 20%) and (18% versus 9%), respectively. Both Jurkat wt and kd cells were more sensitive to 6-TG-induced apoptosis than to 6-MP. 6-TG activity was also more affected by TPMT levels than was 6-MP as reflected by IC60, concentrations that is, 6-MP [4.6 μmol/L (wt) and 4.7 μmol/L (kd)], 6-TG [2.7 μmol/L (wt) and 0.8 μmol/L (kd)]. IC60 concentrations induced significant apoptosis in both Jurkat wt and kd cells (257%, versus 314%) with 6-MP and (323% versus 306%) with 6-TG, respectively. At IC60 (6-MP) 6-thioguanine nucleotides (6-TGN) accumulation in cells was 518 versus 447 pmol/million cells in wt and kd cells, respectively. On the other hand 6-TGN accumulation at IC60 (6-TG) was 477 versus 570 pmol/million cells in wt and kd cells, respectively. 6-Methylated mercaptopurine (6-MeMP) concentrations were more affected than 6-TGN by TPMT kd (194 versus 10 pmol/million cells) in wt and kd cells, respectively.. We conclude that TPMT kd cells are an appropriate in vitro model to investigate the significance of TPMT deficiency with thiopurine therapy and could be helpful in understanding possible clinical consequences of TPMT polymorphism.

Topics: Apoptosis; Cell Line, Tumor; Drug Hypersensitivity; Gene Knockdown Techniques; Guanine Nucleotides; Humans; Immune Tolerance; Jurkat Cells; Mercaptopurine; Methyltransferases; Polymorphism, Genetic; Purine-Pyrimidine Metabolism, Inborn Errors; T-Lymphocytes; Thioguanine; Thionucleotides

Topics: Abnormalities, Drug-Induced; Adult; Aged; Azathioprine; Bone Marrow Diseases; Chemical and Drug Induced Liver Injury; Child; Cost-Benefit Analysis; Drug Administration Schedule; Drug Approval; Drug Costs; Drug Hypersensitivity; Drug Interactions; Female; Genetic Testing; Humans; Immunosuppressive Agents; Infections; Kidney Diseases; Lactation; Male; Methyltransferases; Nausea; Neoplasms; Off-Label Use; Patient Education as Topic; Pregnancy; Risk Factors; Skin Diseases; Thioguanine; Virus Diseases

Measurement of thiopurine metabolite levels may be useful as a clinical tool to optimize thiopurine treatment of paediatric inflammatory bowel disease (IBD).. The authors evaluated correlations between 6-thioguanine nucleotide (6-TGN) and therapeutic response, metabolite levels and drug toxicity.. Fifty-six paediatric IBD patients treated with thiopurines had 326 metabolite level measurements and were retrospectively reviewed. Clinical status and laboratory parameters were compared with metabolite levels.. There was significant correlation between 6-TGN levels and therapeutic response, with higher median 6-TGN levels among patients with therapeutic response than those with non-therapeutic response (194 vs. 146 pmol/8 x 10(8) RBC; P = 0.0004). Patients with 6-TGN levels >235 pmol/8 x 10(8) RBC were more likely to achieve therapeutic response than those below the cut-off (odds ratio, 2.5; 95% CI, 1.5-4.1). Patients who developed leukopenia tended to have higher median 6-TGN levels than those without leukopenia (261 vs. 160 pmol/8 x 10(8) RBC) but the difference was not statistically significant. There was no correlation between 6-methylmercaptopurine levels and hepatotoxicity. Two patients developed acute pancreatitis. Metabolite level measurements were helpful in identifying non-compliance in nine patients.. Monitoring of thiopurine metabolite levels is useful to guide and optimize dosing, as an adjunct to clinical judgement, blood count and liver biochemistry measurements to minimize the risk of drug toxicity and to confirm non-compliance.

Topics: Adolescent; Azathioprine; Chemical and Drug Induced Liver Injury; Child; Child, Preschool; Drug Hypersensitivity; Female; Humans; Immunosuppressive Agents; Infant; Inflammatory Bowel Diseases; Leukopenia; Male; Mercaptopurine; Pancreatitis; Retrospective Studies; Thioguanine; Thrombocytopenia; Treatment Refusal

Approximately 10% of inflammatory bowel disease (IBD) patients receiving 6-mercaptopurine (6-MP) or azathioprine (AZA) develop drug hypersensitivity reactions necessitating early discontinuation of these traditional thiopurines. These allergic reactions typically reoccur upon rechallenge. Our recently published pilot study suggested that thioguanine (6-TG), a closely related thiopurine, was efficacious and well tolerated in IBD patients resistant to 6-MP/AZA. The aim of this study was to determine if hypersensitivity reactions to 6-MP/AZA reoccur with 6-TG therapy.. IBD patients allergic to 6-MP and/or AZA were treated with 6-TG as an alternate thiopurine. Hypersensitivity reactions to 6-MP/AZA must have been documented within 6 wk of 6-MP/AZA initiation.. 6-TG was initiated in 21 IBD patients at a median (range) dose of 20 (10-40) mg/day. 6-TG hypersensitivity reaction occurred in only four of 21 (19%) patients after a median time interval of 9 days. Pancreatitis did not reoccur with 6-TG. Eighty-two percent of 6-TG tolerant patients were assessed as improved at last follow-up.. These results suggest that 6-TG may be considered as a possible alternate thiopurine in patients allergic to traditional 6-MP/AZA. Despite these favorable results, candidates for 6-TG should be selected with caution, and its use should be reserved for IBD patients well informed about potential toxicities.

Topics: Adult; Azathioprine; Drug Hypersensitivity; Female; Humans; Immunosuppressive Agents; Inflammatory Bowel Diseases; Intestinal Mucosa; Male; Mercaptopurine; Middle Aged; Pilot Projects; Prospective Studies; Safety; Thioguanine; Treatment Outcome

Topics: Azathioprine; Drug Hypersensitivity; Humans; Immunosuppressive Agents; Inflammatory Bowel Diseases; Mercaptopurine; Thioguanine

Topics: Animals; Antibodies; Antibody Specificity; Antigens; Autoimmune Diseases; Blood Coagulation Factors; Blood Coagulation Tests; Blood Platelets; Blood Transfusion; Carbamazepine; Drug Hypersensitivity; Haplorhini; Humans; Immune Sera; Immunoglobulin Fragments; Immunoglobulin G; Lupus Erythematosus, Systemic; Myeloma Proteins; Phospholipids; Purpura, Thrombocytopenic; Quinidine; Rabbits; Thioguanine

Topics: Adolescent; Adult; Aged; Allopurinol; Anaphylaxis; Asparaginase; Blood Coagulation Disorders; Cytarabine; Daunorubicin; Drug Hypersensitivity; Female; Fever; Gastrointestinal Hemorrhage; Hallucinations; Humans; Hyperglycemia; Injections, Intravenous; Jaundice; Leukemia, Lymphoid; Leukemia, Myeloid, Acute; Liver; Male; Mercaptopurine; Methotrexate; Middle Aged; Oral Hemorrhage; Prednisone; Thioguanine; Uremia; Vincristine; Vomiting

Topics: Animals; Antigen-Antibody Reactions; Chlorphenesin; Cyclophosphamide; Drug Hypersensitivity; Guinea Pigs; Mercaptopurine; Methotrexate; Muscles; Passive Cutaneous Anaphylaxis; Penicillin G; Serum Albumin, Bovine; Thioguanine