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At least 19 recordsLinked to original sources
PubMed2006

Toxicity of 6-thioguanine: no hepatotoxicity in a series of IBD patients treated with long-term, low dose 6-thioguanine. Some evidence for dose or metabolite level dependent effects?

BACKGROUND: 6-Thioguanine is used in inflammatory bowel disease since 2001, with promising short-term results. In 2003, liver histology of some 6-thioguanine treated patients showed nodular regenerative hyperplasia. Recently, magnetic resonance imaging revealed nodular regenerative hyperplasia in patients with normal histology. AIMS: Investigating the presence of nodular regenerative hyperplasia in long-term 6-thioguanine treated patients. PATIENTS AND METHODS: Inflammatory bowel disease patients, using 6-thioguanine minimally 24 months, were asked to undergo liver biopsy and magnetic resonance imaging. RESULTS: Fourteen patients used 6-thioguanine minimally 24 months, 13 participated. Mean 6-thioguanine therapy duration, daily dose and 6-thioguanine nucleotide levels were: 36 months, 18.8 mg (0.28 mg/kg) and 705 pmol/8x10(8) erythrocytes, respectively. Liver histology and magnetic resonance imaging showed no nodular regenerative hyperplasia. DISCUSSION: Liver biopsy and magnetic resonance imaging showed no nodular regenerative hyperplasia in these long-term 6-thioguanine treated inflammatory bowel disease patients. 6-thioguanine dose and metabolite levels were lower compared with previous nodular regenerative hyperplasia reports, suggesting dose or metabolite level-dependent effects. Otherwise, nodular regenerative hyperplasia is related with inflammatory bowel disease itself and immunosuppressives, including azathioprine and 6-mercaptopurine. CONCLUSION: 6-Thioguanine is debated due to nodular regenerative hyperplasia. We found no nodular regenerative hyperplasia in inflammatory bowel disease patients with long-term, low dosed 6-thioguanine, suggesting metabolite level-dependent effects. Therefore, 6-thioguanine still seems useful, but in selected patients, intolerant for other immunosuppressives, low dosed and under close surveillance of metabolite levels and hepatotoxity.

Adult↗
PubMed1989

Amsacrine, cytarabine and thioguanine (AAT) versus daunorubicin, cytarabine, thioguanine (DAT) in adults with untreated acute non-lymphoblastic leukemia (ANLL). Austrian-German results.

69 patients (median age 53 years, 19-79 years old) with untreated acute non-lymphoblastic leukemia (ANLL) were randomized to receive either a regimen of amsacrine, cytarabine, thioguanine (AAT) or daunorubicin, cytarabine, thioguanine (DAT). AAT consisted of amsacrine 200 mg/m2/day x 5, thioguanine 100 mg/m2/12 h p.o. x 10; DAT was daunorubicin 50 mg/m2/day x 3, cytarabine 200 mg/m2/day x 5, thioguanine 100 mg/m2/12 h p.o. x 10. After one or two induction courses the patients subsequently received 2 consolidation courses. 17 patients were not assessable for response to therapy due to exitus during induction treatment. Complete remission could be obtained in 14/24 (58%) of DAT patients respectively. Patients less than 60 years of age achieved CR in 63% (AAT) vs 65% (DAT), whereas patients greater than or equal to 60 years obtained a CR in 50% (AAT) vs 13% (DAT). Toxicity appears not to be increased significantly with amsacrine. These data indicate that amsacrine could replace daunorubicin in remission induction regimens of ANLL containing cytosin arabinoside and thioguanine without decreasing the response rate.

Adolescent↗
PubMed1991

Thioguanine used in maintenance therapy of chronic myeloid leukaemia causes non-cirrhotic portal hypertension. Results from MRC CML. II. Trial comparing busulphan with busulphan and thioguanine.

Portal hypertension with varices developed in 18/675 patients with chronic myeloid leukaemia (CML) in a randomized trial comparing busulphan with busulphan and thioguanine. All 18 had received the drug combination and none busulphan alone (P less than 0.0001). Ascites was also seen significantly more often in the combination arm (P less than 0.05). These results strongly suggest that the addition of thioguanine was responsible for the development of portal hypertension. The histological features were predominantly those of non-cirrhotic portal hypertension--either idiopathic portal hypertension with minimal morphological abnormalities, nodular regenerative hyperplasia or in two cases leukaemic infiltration only was noted. Cirrhosis was present in 3/16 cases studied. Both treatment groups developed abnormal liver function tests during the chronic phase, but particularly with progression of the disease. During chronic phase abnormalities were significantly more frequent in those receiving busulphan and thioguanine-alkaline phosphatase (P less than 0.02), transaminases (P less than 0.04), bilirubin (P less than 0.05), multiple abnormalities (P less than 0.01). The development of portal hypertension was often associated with abnormalities of these tests; however, lack of specificity precludes their use as a predictor of subsequent clinical problems. Thioguanine confers no survival advantage in this disease. In view of its hepatotoxicity it should not be used routinely for maintenance of control in chronic phase CML.

Alkaline Phosphatase↗
PubMed1978

Specific and sensitive combined high-performance liquid chromatographic-flow fluorometric assay for intracellular 6-thioguanine nucleotides metabolites of 6-mercaptopurine and 6-thioguanine.

A new non-radioisotopic technique is described for measuring rates of intracellular formation by human leukemic blasts of 6-thioguanine nucleotide metabolites, obligatory intermediates in the antineoplastic action of both 6-mercaptopurine and 6-thioguanine itself. The method is both specific and sensitive, and involves combined high-performance liquid chromatography and flow fluormetric detection of oxidized 6-thioquanine nucleotides in alkaline permanganate-treated cell extracts. Non-metabolized 6-thioguanine and 6-thioxanthine are also separated and quantitated in this system, permitting complementary in vivo pharmacokinetic analysis. The assay may be applied to detect resistant disease at an early stage in therapy, and thereby provides the opportunity for alternative treatments to be instituted.

Body Fluids↗
PubMed2001

6-Thioguanine in children with acute lymphoblastic leukaemia: influence of food on parent drug pharmacokinetics and 6-thioguanine nucleotide concentrations.

AIMS: Since relatively little is known about the pharmacokinetics of 6-thioguanine (6TG) in children receiving 6-thioguanine for maintenance therapy of acute lymphoblastic leukaemia (ALL), we studied plasma drug concentrations under standardized conditions and investigated the effect of food on parent drug pharmacokinetics and the accumulation of the active metabolites 6-thioguanine nucleotides (6-TGNs) in red cells. METHODS: Single oral doses of 40 mg of 6-TG were administered both in the fasting and fed state to children with ALL. Pharmacokinetic sampling was performed up to 6 h post dose. Daily oral doses of 40 mg m(-2) of 6-TG were administered both fasting and after food over two 4 week periods. Twice weekly samples were taken for metabolite concentrations. The study design was cross-over with each child receiving dosing in either fasted or after food over a 4 week period in each phase. RESULTS: Eleven patients were studied. A wide interindividual variation in Cmax (median 313 pmol ml(-1), range 51-737) and AUC (median 586 pmol ml(-1) h, range 156-1306) was observed in the fasted state. Concomitant food administration resulted in a significant reduction in Cmax (median 71 vs 313 pmol ml(-1), P = 0.006, CI from 36 to 426), AUC (median 200 vs 586 pmol ml(-1) h, P = 0.006, 95% CI from 109 to 692), and time to reach Cmax (median 1.5 vs 3 h, P = 0.013, 95% CI from 0.74 to 2.73). There was no difference in the steady state concentration of red cell 6-TGNs observed after a 4 week period of 6-TG administered fasting or after food. CONCLUSIONS: Children with ALL demonstrate significant interindividual variation in 6-TG pharmacokinetics. Although there would appear to be a reduction in parent drug Cmax and AUC with food there was no difference in 6-TGN concentrations after 4 weeks of 6-TG. Taking the drug on an empty stomach may not be necessary.

Administration, Oral↗
PubMed2004

Oral treatment of acute myeloid leukaemia with etoposide, thioguanine, and idarubicin (ETI) in elderly patients: a prospective randomised comparison with intravenous cytarabine, idarubicin, and thioguanine in the second and third treatment cycle.

A randomised multicentre study was conducted among patients over 65 yr of age with newly diagnosed acute myeloid leukaemia (AML) to compare oral treatment with etoposide 80 mg/m(2) and thioguanine 100 mg/m(2) twice daily on 5 d and idarubicin 15 mg/m(2) on 3 d (ETI) to a mainly i.v. combination of cytarabine 100 mg/m(2) twice daily on 5 d, idarubicin 12 mg/m(2) x 1, and thioguanine (TAI). Ninety-two patients were enrolled. Their median age was 72 yr, range 65-84 yr. Sixty-five patients had de novo AML, 21 AML subsequent to myelodysplastic syndrome, and six treatment-related AML. They received at first a 6-d i.v. treatment with cytarabine and idarubicin. After the first treatment, 68 patients were randomised to receive two cycles of ETI (n = 36) or TAI (n = 32) and thereafter maintenance with mercaptopurine and methotrexate. Of the 92 patients, 52 (57%) achieved remission at some stage. The median survival was 10 months. There were no significant differences between the patients randomised to ETI or TAI in the remission rate (67% vs. 72%), survival (12 months from randomisation in both arms), event-free survival or relapse rate. The patients randomised to receive ETI spent significantly fewer days at hospital during the two randomised cycles (20 vs. 41 d, P = 0.010), and they had fewer days with infusions, shorter neutropenias and thrombocytopenias and fewer and less severe infections. In conclusion, treatment with oral ETI resulted in a similar antileukaemic effect as obtained with mainly i.v. TAI, with less toxicity and reduced need for hospitalisation.

Administration, Oral↗
PubMed1983

Assay of 6-thioguanine nucleotide, a major metabolite of azathioprine, 6-mercaptopurine and 6-thioguanine, in human red blood cells.

An assay for 6-thioguanine (6-TG) nucleotide, a major metabolite of the cytotoxic drugs azathioprine, 6-mercaptopurine and 6-thioguanine in human red blood cells (RBCs) has been developed. The metabolite was not detected in RBCs when azathioprine or 6-mercaptopurine was incubated with whole blood in-vitro. The assay for intracellular 6-TG nucleotide is specific and requires 8 X 10(8) RBCs (100 microliters packed cells) for which the limit of sensitivity is 30 pmole 6-TG nucleotide. Pre-dose blood samples were obtained, 12 h after the last azathioprine dose, from 10 renal transplant recipients with stable functioning cadaver grafts on a total daily dose of 150 mg azathioprine. The mean 6-TG nucleotide concentration was 171 pmole/8 X 10(8) RBCs (s.d. = 84). The assay is also suitable for use in measuring 6-TG nucleotide in the RBCs of leukaemic children undergoing 6-mercaptopurine treatment.

Azathioprine↗
PubMed1999

Thioguanine administered as a continuous intravenous infusion to pediatric patients is metabolized to the novel metabolite 8-hydroxy-thioguanine.

Thiopurine antimetabolites have been in clinical use for more than 40 years, yet the metabolism of thiopurines remains only partially understood. Data from our previous pediatric phase 1 trial of continuous i.v. infusion of thioguanine (CIVI-TG) suggested that TG was eliminated by saturable mechanism, with conversion of the drug to an unknown metabolite. In this study we have identified this metabolite as 8-hydroxy-thioguanine (8-OH-TG). The metabolite coeluted with the 8-OH-TG standard on HPLC and had an identical UV spectrum, with a lambda(max) of 350 nm. On mass spectroscopy, the positive ion, single quad scan of 8-OH-TG yielded a protonated molecular ion at 184 Da and contained diagnostic ions at m/z 167, 156, 142, and 125 Da. Incubation of TG in vitro with partially purified aldehyde oxidase resulted in 8-OH-TG formation. 8-OH-TG is the predominant circulating metabolite found in patients receiving CIVI-TG and is likely generated by the action of aldehyde oxidase.

Aldehyde Oxidase↗
PubMed1999

Delayed cytotoxicity of 6-mercaptopurine is compatible with mitotic death caused by DNA damage due to incorporation of 6-thioguanine into DNA as 6-thioguanine nucleotide.

Many protocol studies have shown that low dose 6-mercaptopurine (6MP) in maintenance chemotherapy for childhood acute lymphoblastic leukemia (ALL) can be utilized to cure the disease. Mitotic or reproductive cell death has been recognized after G2 arrest when cells are treated with antitumor agents. The precise mechanism of mode of action of 6MP still remains unclear. We found delayed cytotoxic effect of 6MP in P388 murine leukemic cells. Morphological study showed that 6MP induced delayed death was characterized by an enlargement of cell size and multinucleated nuclei. Agarose gel electrophoresis of fragmented DNA from cells treated with 6MP showed the typical ladder pattern. These findings were compatible with mitotic death. Our results make us hypothesize that the delayed cytotoxicity of 6MP is one of the drug induced mitotic deaths caused by DNA damage due to incorporation of 6-thioguanine (6TG) into DNA as thioguanine nucleotide (TGN). Mitotic death may be a mechanism for killing the cycling cells from residual leukemic cells in G0 or long G1 phases in the treatment of childhood ALL.

Animals↗
PubMed1981

Efficiency of isolation of revertible 6-thioguanine resistant clones is dependent on the concentration of thioguanine used for selection.

The availability of a number of well characterised mammalian cell mutants which revert at measurable frequencies when exposed to specific chemical mutagens would considerably aid analysis of mechanisms of mutagenesis in mammalian cells, might ultimately provide the mammalian cell equivalent of the "Ames' tester strains and could aid the understanding of the spectrum of mutations produced by different carcinogens. As an approach to this goal we have analysed the phenotypes and revertibility of a considerable number of 6-thioguanine resistant (6TGR) mutants isolated from V79 cells and have determined the 6TG concentration which yields the optimum number of revertible cell lines.

Animals↗
PubMed1978

Daunomycin, cytosine arabinoside and 6-thioguanine (DAT) vs vincristine, cytosine arabinoside and 6-thioguanine (VAT) in the induction treatment of acute nonlymphocyte leukemia: a randomized collaborative study.

One hundred patients were entered in a cooperative study comparing the efficacy of two different regimens in the induction treatment of acute nonlymphocytic leukemia (ANLL). Patients were randomly allocated to receive either the DAT or VAT combination; half of the patients were also randomized to receive CNS prophylaxis including intrathecal methotrexate + prednisone and cranial irradiation. Consolidation and maintenance therapy were uniform in responding patients. Out of 82 evaluable patients 41 (50%) attained complete remission (CR) with no significant difference between the two regimens. Median remission duration was slightly longer in the DAT group (32.5 vs 22 weeks); median survival was 34 weeks for all evaluable patients with no difference between the two schedules. Meningeal relapse occurred only in two patients after 19 and 99 weeks of continuous remission. Fourteen patients are still alive after 61 to greater than or equal to 155 weeks, of whom seven are in their initial remission (six in the DAT and one in the VAT group). We conclude that 1) DAT and VAT are equally effective in inducing CR in a high proportion of ANLL patients; 2) until marrow remission can be prolonged significantly, preventing CNS leukemia will not have any significant impact of the course of ANLL.

Adolescent↗
PubMed2004

Thioguanine-nucleotides do not predict efficacy of tioguanine in Crohn's disease.

BACKGROUND: 6-Thioguanine-nucleotides seem to be the active metabolites of thiopurine therapy, and their monitoring has been considered a useful tool for optimizing response in inflammatory bowel diseases. Tioguanine (thioguanine) therapy results in much higher levels of 6-thioguanine-nucleotide levels when compared with azathioprine or mercaptopurine. AIM: To elucidate the influence of 6-thioguanine-nucleotide and methylated 6-thioguanine-nucleotide levels under tioguanine on efficacy and toxicity in Crohn's disease. METHODS: 6-Thioguanine-nucleotide and methylated 6-tioguanine-nucleotide levels were measured regularly in 26 Crohn's disease patients treated with tioguanine. Nucleotide levels were related to efficacy and toxicity. RESULTS: 6-Thioguanine-nucleotide levels rose very high [median 1241 pmol/8 x 10(8) red blood cells (range 313-1853)]. Methylated 6-thioguanine-nucleotide levels were detected in all patients [491 pmol/8 x 10(8) red blood cells (154-1775)]. 6-Thioguanine-nucleotide and methylated 6-thioguanine-nucleotide concentrations correlated significantly (r = 0.7, P < 0.0001). Nucleotide levels from patients achieving remission (n = 14) did not differ significantly from non-remitters (n = 12) [6-thioguanine-nucleotide: 1077 (599-2160) vs. 1210 (534-4665); methylated 6-thioguanine-nucleotide: 510 (214-1222) vs. 421 (145-1284)]. One patient with intermediate thiopurine S-methyltransferase activity experienced bone marrow toxicity upon dose escalation parallel with excessively high thioguanine-nucleotide levels. CONCLUSIONS: 6-Thioguanine-nucleotide as well as methylated 6-thioguanine-nucleotide levels under tioguanine therapy were not related to efficacy. This suggests that monitoring of 6-thioguanine-nucleotide levels is not a useful tool to predict response to thiopurines.

Adult↗
PubMed1988

A novel class of unstable 6-thioguanine-resistant cells from dog and human kidneys.

Thioguanine-resistant primary clones were grown from single cell suspensions obtained from dog and human kidneys by enzymatic digestion. In medium containing a relatively high concentration (10 micrograms/ml) of thioguanine, thioguanine-resistant primary clones arose from each source at frequencies ranging from 10(-4) to 10(-5). A reduction in total hypoxanthine uptake was found in the thioguanine-resistant primary clones which had developed in thioguanine medium, consistent with a reduction in hypoxanthine phosphoribosyltransferase activity. When these thioguanine-resistant primary clones were subsequently grown in the absence of thioguanine and assayed for the thioguanine-resistant phenotype and hypoxanthine phosphoribosyltransferase activity, it was found that most were now thioguanine-sensitive and yielded cell-free extracts with substantial amounts of hypoxanthine phosphoribosyltransferase activity. In contrast, thioguanine-resistant human clones grown continuously in the presence of thioguanine yielded cell-free extracts with little or no detectable hypoxanthine phosphoribosyltransferase activity. Southern blot analysis demonstrated no structural alterations in the hypoxanthine phosphoribosyltransferase gene in thioguanine-resistant primary human kidney clones. These results suggest that a novel mechanism(s) for thioguanine resistance and the control of hypoxanthine phosphoribosyltransferase expression may occur in dog and human kidney cells.

Animals↗
PubMed1981

Clinical pharmacology of oral thioguanine in acute myelogenous leukemia.

Although thioguanine has been in clinical use for over 20 years, few data are yet available on the clinical pharmacology of thioguanine administered orally. We have studied the plasma thioguanine levels in acute myelogenous leukemia patients during remission induction (daunomycin 60 mg/m2 on day 1, arabinosylcytosine 200 mg/m 2. day for 7 days by infusion, thioguanine 100 mg/m2 PO every 12 h for 7 days) and remission maintenance (arabinosylcytosine 200 mg/m2 . day for 4 days by infusion, thioguanine 100 mg/m2 PO every 12 h for 4 days). Hourly blood samples were taken after thioguanine administration, and plasma thioguanine levels were measured by high-performance liquid chromatography with an anion-exchange column. Prior to the chromatography the thioguanine was oxidized by alkaline potassium permanganate to the corresponding 6-sulfonate, which was monitored by means of fluorescence detection. Peak plasma levels of thioguanine were observed 2-4 h after administration and varied from 0.03-0.94 microM. Plasma levels of thioguanine were markedly lower in patients with severe nausea and emesis. Food intake at the same time as thioguanine administration also tended to lower plasma drug levels. The 30-fold range in thioguanine plasma levels observed in this study suggests that intermittent IV administration may provide a better means of standardizing the dosage of thioguanine.

Chromatography, Ion Exchange↗
PubMed1984

Synergistic interaction between acivicin (AT-125) and 6-thioguanine in the murine leukemia L1210. Biochemical and cytokinetic considerations.

The effect of the purine antagonist acivicin (AT-125) on the metabolism and cytotoxicity of 6-thioguanine was examined in the murine leukemia L1210. Cells exposed to 5 X 10(-6) M acivicin for 18 hr followed by 10(-5) M [14C]-6-thioguanine for 2 hr accumulated 2.90 +/- 0.17 nmoles 6-thioguanine/10(6) cells compared to 0.69 +/- 0.07 nmoles 6-thioguanine/10(6) cells in untreated controls. Intracellular accumulation of 6-thioguanine monophosphate, a lethal 6-thioguanine metabolite, increased from 0.27 +/- 0.05 to 1.08 +/- 0.13 nmoles 6-thioguanine monophosphate/10(6) cells following the same acivicin exposure. A similar increment was observed for the formation of 6-thioguanine triphosphate. These alterations in 6-thioguanine metabolism were associated with an increase in the intracellular level of 5-phosphoribosyl-1-pyrophosphate, an obligatory substrate in 6-thioguanine activation (57.9 +/- 7.6 vs 13.4 +/- 2.3 ng 5-phosphoribosyl-1-pyrophosphate/10(6) cells). In contrast, there was a 50% reduction in the amount of 6-thioguanine incorporated into RNA and DNA following acivicin pretreatment. Cytofluorometric analysis revealed that an 18-hr exposure to 5 X 10(6) M acivicin increased the population 5-phase cells, which are more sensitive to the actions of 6-thioguanine, by 50% relative to untreated controls. In both suspension culture growth and soft agar studies, the sequential administration of acivicin followed by 6-thioguanine resulted in substantial growth inhibitory activity; in contrast, the effects of the reverse sequence were subadditive. Pretreatment of L1210 cells with acivicin potentiates the action of subsequently administered 6-thioguanine, and the mechanism may involve both biochemical as well as cytokinetic factors. In vivo studies involving the sequential administration of these agents appear warranted.

Animals↗
PubMed1992

Effect of 6-thioguanine on Chlamydia trachomatis growth in wild-type and hypoxanthine-guanine phosphoribosyltransferase-deficient cells.

Chlamydiae have evolved a biphasic life cycle to facilitate their survival in two discontinuous habitats. The unique growth cycle is represented by two alternating forms of the organism, the elementary body and the reticulate body. Chlamydiae have an absolute nutritional dependency on the host cell to provide ribonucleoside triphosphates and other essential intermediates of metabolism. This report describes the pleiotropic effects of the purine antimetabolite 6-thioguanine on chlamydial replication. In order to display cytotoxicity, 6-thioguanine must first be converted to the nucleotide level by the host cell enzyme hypoxanthine-guanine phosphoribosyltransferase. Our results show that 6-thioguanine is an effective inhibitor of chlamydial growth with either wild-type or hypoxanthine-guanine phosphoribosyltransferase-deficient cell lines as the host. Interestingly, the mechanism of 6-thioguanine-induced inhibition of chlamydial growth is different depending on which cell line is used. With wild-type cells as the host, the cytotoxic effects of 6-thioguanine on chlamydial growth are relatively fast and irreversible. Under these circumstances, cytotoxicity likely results from the combined effect of starving chlamydiae for purine ribonucleotides and incorporation of host-derived 6-thioguanine-containing nucleotides into chlamydial nucleic acids. With hypoxanthine-guanine phosphoribosyltransferase-deficient cells as the host, 6-thioguanine must be present at the start of the chlamydial infection cycle to be effective and the growth inhibition is reversible upon removal of the antimetabolite. These findings suggest that in hypoxanthine-guanine phosphoribosyltransferase-deficient cells, the free base 6-thioguanine may inhibit the differentiation of elementary bodies to reticulate bodies. With hypoxanthine-guanine phosphoribosyltransferase-deficient cells as the host, 6-thioguanine was used as a selective agent in culture to isolate a Chlamydia trachomatis isolate resistant to the effects of the drug. This drug resistant C. trachomatis isolate was completely resistant to 6-thioguanine in hypoxanthine-guanine phosphoribosyltransferase-deficient cells; however, it displayed wildtype sensitivity to 6-thioguanine when cultured in wild-type host cells.

Adenine Phosphoribosyltransferase↗
PubMed2006

The thiopurine methyltransferase genetic polymorphism is associated with thioguanine-related veno-occlusive disease of the liver in children with acute lymphoblastic leukemia.

OBJECTIVE: Thiopurine metabolism was investigated in children with acute lymphoblastic leukemia treated in the United Kingdom Medical Research Council trial ALL97. This trial compared the efficacy and toxicity of thioguanine (INN, thioguanine) versus mercaptopurine. METHODS: Consecutive children were randomized to receive thioguanine or mercaptopurine during maintenance chemotherapy. Toxicity data were collected by an adverse event-reporting system with follow-up questionnaires. Red blood cell thiopurine methyltransferase (TPMT) activity and thioguanine nucleotide concentrations were measured by standard techniques. RESULTS: Of the children, 748 were randomized to thioguanine and 744 were randomized to mercaptopurine. There was no difference in the event-free survival rate between the 2 groups (80% and 81%, respectively, at 5 years). Thioguanine was associated with veno-occlusive disease (VOD) of the liver in 95 children, and persistent splenomegaly as a result of portal hypertension developed in 43 children. TPMT activity was significantly lower in the children in whom VOD developed, with a median of 13.4 U (range, 5.8-23 U) compared with 15.2 U (range, 5.3-27) in a control group of 161 leukemia patients in whom VOD did not develop (median difference, 1.8 U; 95% confidence interval, 0.9-2.7 U; P = .0001). TPMT activity in children with persistent splenomegaly was also lower than that in control subjects (median difference, 1.6 U; 95% confidence interval, 0.3-2.8 U; P = .012). There was no difference in red blood cell thioguanine nucleotide concentrations. CONCLUSIONS: Thioguanine was associated with liver damage in 11% of children randomized to thioguanine without an improvement in event-free survival rate. The association of lower TPMT activity with thioguanine-related liver damage could provide a means of identifying at-risk patients.

Adolescent↗