Therapeutic drug monitoring of thiopurine metabolites in adult thiopurine tolerant IBD patients on maintenance therapy

BACKGROUND AND AIMS

Therapeutic drug monitoring of active metabolites of thiopurines, azathioprine and 6-mercaptopurine, is relatively new. The proposed therapeutic threshold level of the active 6-thioguanine nucleotides (6-TGN) is ≥235 pmol/8×10(8) erythrocytes. The aim of this prospective cross-sectional study was to compare 6-TGN levels in adult thiopurine tolerant IBD patients with an exacerbation with those in remission, and to determine the therapeutic 6-TGN cut-off level.

METHODS

Hundred IBD patients were included. Outcome measures were thiopurine metabolite levels, calculated therapeutic 6-TGN cut-off level, CDAI/CAI scores, thiopurine dose and TPMT enzyme activity.

RESULTS

Forty-one patients had an exacerbation, 59 patients were in remission. In 17% of all patients 6-TGN levels were compatible with non-compliance. The median 6-TGN levels were not significantly different between the exacerbation and remission group (227 versus 263 pmol/8×10(8) erythrocytes, p=0.29). The previous reported therapeutic 6-TGN cut-off level of 235 pmol/8×10(8) erythrocytes was confirmed in this study. Twenty-six of the 41 patients (63%) with active disease had 6-TGN levels below this threshold and 24 of 59 IBD patients (41%) in clinical remission (p=0.04).

CONCLUSIONS

Thiopurine non-compliance occurs frequently both in active and quiescent disease. 6-TGN levels below or above the therapeutic threshold are associated with a significant higher chance of IBD exacerbation and remission, respectively. These data support the role of therapeutic drug monitoring in thiopurine maintenance therapy in IBD to reveal non-compliance or underdosing, and can be used as a practical tool to optimize thiopurine therapy, especially in case of thiopurine non-response.

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.

Pharmacokinetics of 6-thioguanine in patients with inflammatory bowel disease

6-Thioguanine (6-TG) seems to be an attractive alternative in both AZA- and 6-MP-intolerant and -resistant IBD populations. However, little is known of 6-TG pharmacokinetics, metabolite levels, and their correlation with drug efficacy and toxicity in IBD patients. This study reports the 6-TG pharmacokinetics in a population of IBD patients and the predictive value of metabolite concentrations. Red blood cell (RBC) 6-thioguanine nucleotide (6-TGN) concentrations were measured in 28 IBD patients at t = 1, 2, 4, and 8 weeks after starting 6-TG, 20 mg once daily. Outcome measures included mean 6-TGN concentrations (+/-95% confidence interval [CI95%]) and their associations with TPMT genotype, 6-TG dose, and hematological, hepatic, pancreatic, and efficacy parameters during the 8 week period. Steady-state 6-TGN concentrations were reached after 4 weeks, indicating a half-life of approximately 5 days, and measured 856 (CI95% 715-997) pmol/8 x 10 RBCs. Large interpatient variability occurred at all time-points. No correlation was found between steady-state 6-TGN concentrations and drug dose per kilogram body weight. No significant differences in 6-TGN concentrations were found between patients with adverse events and patients without any event. Also, mean 6-TGN concentrations did not differ in patients with active disease versus patients in remission. In IBD patients on 6-TG treatment, large interindividual differences in metabolite concentrations occur. In our population, we could not demonstrate a clear relationship between 6-TGN concentrations on one hand and toxicity and efficacy on the other, as exist in AZA- and 6-MP-treated patients.

The pharmacokinetic effect of discontinuation of mesalazine on mercaptopurine metabolite levels in inflammatory bowel disease patients

BACKGROUND

In vitro studies suggest interactions between mesalazine (mesalamine) and thiopurines by thiopurine S-methyltransferase (TPMT) inhibition, influencing the balance of hepatotoxic 6-methylmercaptopurine ribonucleotide and immunosuppressive tioguanine (thioguanine) metabolites.

AIM

To examine the in vivo pharmacokinetic interaction between mesalazine and mercaptopurine.

METHODS

A prospective study was performed in quiescent inflammatory bowel disease patients using the combination of mercaptopurine and mesalazine. Laboratory parameters, 6-methylmercaptopurine ribonucleotide and tioguanine levels and thiopurine S-methyltransferase activity in erythrocytes were measured at stable medication, after mesalazine discontinuation and mesalazine reintroduction, further mercaptopurine was continued.

RESULTS

Seventeen patients were participated. Mean mercaptopurine dose was 0.78 mg/kg/day and median of mesalazine dose was 3000 mg/day. After mesalazine discontinuation, mean tioguanine levels changed significantly from 262 to 209 pmol/8 x 10(8) red blood cell, increasing to 270 after reintroduction. Mean 6-methylmercaptopurine ribonucleotide levels were 1422, 2149 and 1503 pmol/8 x 10(8) red blood cell respectively. Mean 6-methylmercaptopurine ribonucleotide/tioguanine ratio increased significantly from 6.3 at baseline to 11.2. Mean baseline thiopurine S-methyltransferase activity was 0.58 pmol/10(6) red blood cell/h and stable. All patients had wild-type thiopurine S-methyltransferase genotypes however, leucocyte counts were stable.

DISCUSSION

A significantly higher tioguanine levels and improving 6-methylmercaptopurine ribonucleotide/tioguanine ratio were found during mesalazine/mercaptopurine combination. Theoretically, mesalazine inhibits thiopurine S-methyltransferase activity. In vivo thiopurine S-methyltransferase activity did not change, however.

CONCLUSION

Mesalazine has synergistic effects on mercaptopurine therapy, but the mechanism is unclear. Combining these drugs may be further indication for mesalazine in inflammatory bowel disease treatment.

Pharmacokinetics of 6-mercaptopurine in patients with inflammatory bowel disease: implications for therapy

Proper prospective pharmacokinetic studies of 6-mercaptopurine (6-MP) in inflammatory bowel disease (IBD) patients are lacking. As a result, conflicting recommendations have been made for metabolite monitoring in routine practice. The authors have evaluated 6-MP pharmacokinetics in IBD patients, including the genetic background for thiopurine methyltransferase (TPMT). Red blood cell (RBC) 6-thioguanine nucleotide (6-TGN) and 6-methylmercaptopurine ribonucleotide (6-MMPR) concentrations were measured in 30 IBD patients at 1, 2, 4, and 8 weeks after starting 6-MP, 50 mg once daily. Outcome measures included mean 6-TGN and 6-MMPR concentrations (+/- 95% confidence interval, CI95%) and their associations with TPMT genotype, 6-MP dose, and hematologic, hepatic, pancreatic, and efficacy parameters during the 8-week period. Steady-state concentrations were reached after 4 weeks, indicating a half-life of approximately 5 days for both 6-TGN and 6-MMPR; the concentrations were 368 (CI95% 284-452) and 2837 (CI95% 2101-3573) pmol/8 x 10 RBCs, respectively. Large interpatient variability occurred at all time points. TPMT genotype correlated with 6-TGN concentrations (0.576, P < 0.01), and patients with mutant alleles had a relative risk (RR) of 12.0 (CI95% 1.7-92.3) of developing leukopenia. A 6-MMPR/6-TGN ratio less than 11 was associated with therapeutic efficacy. Based on this pharmacokinetic analysis, therapeutic drug monitoring is essential for rational 6-MP dosing.

Some cases demonstrating the clinical usefulness of therapeutic drug monitoring in thiopurine-treated inflammatory bowel disease patients

The thiopurines azathioprine and 6-mercaptopurine (6-MP) are effective drugs in steroid-dependent and refractory inflammatory bowel disease patients. Therapeutic drug monitoring (TDM) is a new concept to improve drug efficacy and prevent toxic adverse events. As thiopurine metabolism is influenced by genetic polymorphisms of methylating enzymes, metabolite levels may vary considerably, enabling significant adverse effects. In the present paper five patients are described to demonstrate the clinical usefulness of TDM when applying thiopurines for inflammatory bowel disease. Emphasized are patients with liver function test abnormalities and myelosuppression due to inappropriate 6-MP metabolite levels, and subsequently the treatment of these events. In addition, sophisticated 6-MP metabolite level-guided therapy, including non-compliance, is demonstrated. These cases demonstrate that TDM may improve effectivity and safety of thiopurine treatment.

Therapeutic Drug Monitoring in???Patients with Inflammatory Bowel???Disease and Established Azathioprine Therapy

BACKGROUND AND OBJECTIVE

Azathioprine is widely used in the treatment of corticosteroid-dependent and refractory inflammatory bowel disease (IBD). The efficacy of this treatment is based on the production of 6-thioguanine nucleotides, but extremely elevated levels may cause bone marrow suppression. Other azathioprine metabolites, 6-methylmercaptopurine ribonucleotides, are associated with hepatotoxicity. Therapeutic drug monitoring (TDM) may be of help in optimising azathioprine treatment, but data on TDM in established azathioprine therapy are lacking. We therefore measured metabolite levels in a small cohort of patients established on azathioprine therapy.

PATIENTS AND METHODS

6-Thioguanine (6-TGN) and 6-methylmercaptopurine (6-MMP) levels in erythrocytes were measured in 15 IBD outpatients established on azathioprine therapy for at least 3 months at baseline and 1, 4 and 8 weeks after inclusion (mean duration of treatment 28 months; range 7-67 months). Disease activity was evaluated by the Crohn's Disease Activity Index (Crohn's disease) or Truelove-Witts (ulcerative colitis) scores. Metabolite levels were measured by modified high-performance liquid chromatography assay (HPLC). Primary outcome measures were 6-TGN and 6-MMP metabolite levels and 95% confidence intervals (CIs). SECONDARY OUTCOMES were correlations between metabolite levels, drug dose, disease activity and laboratory parameters and compliance.

RESULTS

One patient had active disease during the study period. Eleven of 15 patients (73%) completed the 8-week study period. Dropout reasons were noncompliance in three patients (20%) and intolerance in one patient (7%).

PRIMARY OUTCOMES

At baseline mean 6-TGN levels were 158 (95% CI 113, 203) pmol/8.10(8) RBC (red blood cells), steadily increasing over the 8-week study period, but not significantly. Two patients had zero levels. Another two had significantly increasing levels also suggesting noncompliance. Mean 6-MMP levels showed almost a similar pattern. At baseline, levels were 2213 (95% CI 722, 3704) pmol/8.10(8) RBC.

SECONDARY OUTCOMES

A correlation was found between all RBC 6-MMP levels and azathioprine dose (mg/kg bodyweight) [r = 0.43, p = 0.001] and also between the 6-MMP/6-TGN ratio and azathioprine dose (mg/kg) [r = 0.36, p = 0.010). There was no correlation between RBC 6-TGN or 6-MMP levels and haematological parameters or disease activity scores. No hepatic, pancreatic or myelotoxicity occurred.Thirteen of 15 patients (87%) had baseline steady-state 6-TGN levels below the therapeutic threshold of 235 pmol/8.10(8) RBC. Forty percent (6/15) of our patients were noncompliant; TDM revealed this noncompliance in four of the six patients (27% of all patients).

CONCLUSION

Our small study demonstrates that TDM may provide insight into individual pharmacokinetics. However, TDM does not seem to be useful in patients with IBD established on azathioprine therapy and without disease activity, although it may be helpful in cases of worsening IBD activity to elucidate noncompliance or inefficient treatment.

Upper gastrointestinal endoscopy in patients aged 85 years or more. Results of a feasibility study in a district general hospital

We performed a cross sectional analysis of the feasibility and yield of upper gastrointestinal endoscopy (UGE) in a cohort of patients aged 85 years or more. The study involved 218 patients who underwent diagnostic upper gastrointestinal endoscopy in a district general hospital between 1994 and 1998. Indication, use of sedation, endoscopic findings and treatment after endoscopy were evaluated. Indications for gastroscopy were suspicious of upper gastrointestinal bleeding (UGI) bleeding (41%), anemia (15%), and presence of dyspeptic- (31%), alarm- (9%) and/or reflux symptoms (3%). Serious UGI disease (cancer, peptic ulcer, reflux oesofagitis and/or erosive gastritis/duodenitis) was detected in 97 patients (44%). With respect to clinical presentation, serious UGI disease was present in 61% with bleeding, in 57% with reflux symptoms, in 42% with alarm symptoms, in 33% with anemia and in 28% with dyspepsia. Carcinoma was detected in eight patients (3.8%), all of them were treated with supportive care. In very old people gastroscopy is generally performed on sound indications reveals serious UGI disease in almost one out of two patients, markedly influences medical treatment, and reveals low malignancy rates (3.8%). In these patients, UGE is worthwhile and should not be omitted because of age considerations.

High incidence of inflammatory bowel disease in The Netherlands: results of a prospective study. The South Limburg IBD Study Group

PURPOSE

To gain recent epidemiologic information about inflammatory bowel disease in The Netherlands, a prospective study over four years (1991-1995) was performed.

METHODS

The incidence of inflammatory bowel disease and its subgroups was examined using standardized reports of newly diagnosed patients. A separate study compared the Inflammatory Bowel Disease Registration and computerized diagnostic files of a subgroup of general practitioners with the aim of estimating completeness of case ascertainment.

RESULTS

The following mean incidence rates (per 100,000 inhabitants and year) were found: 6.9 (95 percent confidence interval, 5.9-7.9) for Crohn's disease, 10 (95 percent confidence interval, 8.7-11.2) for ulcerative colitis (23 percent of these with ulcerative proctitis), and 1.1 (95 percent confidence interval, 0.7-1.5) for indeterminate colitis. In the age category 20 to 29 years, the incidence rate of Crohn's disease with small-bowel involvement was higher in females than in males. In extended ulcerative colitis, a male preponderance was observed in the older age groups. Estimated case ascertainment was 78 percent.

CONCLUSIONS

Compared with recent studies in neighboring countries, the observed age and gender standardized incidence rates are high in the south of The Netherlands. Completeness of case ascertainment might have contributed to this observation; however, case ascertainment was low in ulcerative proctitis. In the study area, differences in age and gender standardized incidence rates and in disease localizations could be compatible with an influence of environmental risk factors.

An uncommon cause of anaemia in ulcerative colitis

A 56-year-old woman is reported with severe ulcerative colitis who developed a corticosteroid-resistant haemolytic anaemia. The pathogenesis and treatment options in ulcerative-colitis-related haemolytic anaemia are discussed.

Ursodeoxycholic acid treatment in a patient with primary biliary cirrhosis

A women with stage I-II primary biliary cirrhosis was treated with ursodeoxycholic acid (UDCA). During UDCA treatment a notable improvement in biochemical liver profile was achieved. Liver histology did not deteriorate after one year UDCA. UDCA offers a promising non-toxic alternative in the treatment of PBC.

Efficacy of diltiazem in the treatment of diffuse oesophageal spasm

Calcium antagonist relax smooth muscle, a possible useful concept in treatment of diffuse oesophageal spasm. Therefore the effects of oral diltiazem (60 mg t.d.s.) and placebo were compared in eight patients with diffuse oesophageal spasm in a 10-week double-blind crossover study. The patients recorded the severity of chest pain and/or dysphagia in daily pain diaries using visual analogue scales. Chest pain index and dysphagia index were calculated by multiplying frequency with daily intensity of each individual symptom. When compared to placebo, diltiazem did not significantly change the overall dysphagia index and chest pain index. An individual sizeable reduction of dysphagia was attained on diltiazem in four out of six patients and in six out of eight patients suffering from chestpain. Side effects were not seen during diltiazem therapy. Diltiazem, in our study, did not yield in a significant improvement of symptoms in diffuse oesophageal spasm. Diltiazem, however, can offer relief in selected individual patients suffering from diffuse oesophageal spasm.

Sucralphate-technetium scintigraphy in inflammatory bowel disease: experience in 23 patients

Serial abdominal scanning after the oral administration of sucralphate-99mTc was performed in order to determine the extent of active inflammatory bowel disease in 15 patients with Crohn's disease and in 8 patients with ulcerative colitis. Scintigraphic data were compared with those obtained by endoscopy and radiology in all patients. True positive scans were obtained in 6 (40%) patients with Crohn's disease and in 3 (38%) patients with ulcerative colitis. Overall, sensitivity was higher in colonic disease than that in ileal disease. In 4 (17%) patients, false negative scans were obtained and in the remaining 10 (44%) patients, localisation of the inflammatory bowel disease by the isotope was completely inaccurate. Since sensitivity of the sucralphate-99mTc scintigraphy appears to be low, its widespread use in the screening for inflammatory bowel disease or in assessing the extent of disease involvement cannot be advocated at this moment.

Clinical relevance of lysozyme in the faeces

To elucidate the value of faecal lysozyme determination in the differential diagnosis of patients with atypical abdominal complaints, stool samples of healthy controls, patients with irritable bowel syndrome (IBS) and inflammatory bowel disease (IBD) were analysed. Faecal lysozyme concentration in healthy controls ranged from 0 to 6 mg/l with a mean of 3 mg/l. Patients with IBS had similar faecal lysozyme levels. In contrast, faecal lysozyme concentrations in patients with IBD were increased (range 6 to 104 mg/l). The difference between patients with IBS and IBD was highly significant (P less than 0.001). The determination of faecal lysozyme concentration may provide a useful test in the work-up of patients with abdominal complaints. In addition, the faeces lysozyme concentration appeared to be an objective parameter of the inflammatory activity of IBD in 11 patients investigated.

Faecal lysozyme: determination, reference intervals and some data in gastro-intestinal disease

After diluting faecal samples with a solution of Brij and saline and subsequently ultrafiltrating the faecal mixtures, lysozyme concentration can be reproducibly measured in the obtained faecal fluids, using a turbidimetric method. Measuring faecal lysozyme concentration enables discrimination normal individuals and patients with irritable bowel syndrome between patients with inflammatory bowel disease and colonic cancer. Lysozyme distribution in stools appears to be homogeneous. Faecal lysozyme concentration is stable when samples are stored during at least 1 wk at 6 degrees C. It appears that the lysozyme activity is directly correlated with the clinical status and severity of the disease. Faecal lysozyme may thus serve as an important tool both in diagnosis and in follow-up in the out-patients clinic for gastroenterology.

A new method for chemical analysis of faeces

By using a centriflo membrane cone filter it has become possible to obtain an ultrafiltrate from a 24-h stool specimen. In this faecal fluid several clinical chemical parameters were analysed, such as pH, osmolality, creatinine, sodium, potassium, calcium, magnesium, chloride, bicarbonate, phosphate and lactate. Reference intervals for these substances were obtained in healthy individuals. The data of this control group were compared to those of patients with diarrhoea due to active inflammatory bowel disease, irritable bowel syndrome, lactose intolerance and persons with an ileostomy.

Energy intake and the appearance of 5,8,11-eicosatrienoic acid in serum lipids during parenteral nutrition without fat

During parenteral nutrition without fat, biochemical changes in fatty acid composition of serum lipids may occur, such as a decrease in the concentration of linoleic and arachidonic acid and an increase of 5,8,11-eicosatrienoic acid. In various reports on essential fatty acid deficiency in parenteral nutrition, the rates and degrees of these changes in fatty acid composition of serum lipids are different. We have tested the hypothesis that a relationship exists between the energy intake and the increase in 5,8,11-eicosatrienoic acid in parenteral nutrition without fat. The hypothesis is based on the assumption that mobilization of lipids from body fat, and thus of stored essential fatty acids, only takes place when energy intake is below requirements. Seventeen patients with gastrointestinal diseases were fed parenterally without fat during 1 to 5 weeks (mean 3.5 week). The energy supply to the patients varied from 88 to 222 kilo Joules per kilogram per day. In all patients, the fatty acid pattern of the serum phospholipid fraction was determined weekly. It appeared that those patients with the highest energy intake per kilogram body weight showed the lowest increase in 5,8,11-eicosatrienoic acid. In ten patients, energy was given as glucose and fructose, in seven patients as sorbitol. The type of carbohydrate investigated did not influence the changes in the fatty acid pattern. Results show further that the individual values of the concentrations of 5,8,11-eicosatrienoic acid and of arachidonic acid provide more information concerning the essential fatty acid status of a patient than the commonly used ratio of these two fatty acids.

Total parenteral nutrition in Crohn's disease

A personal experience involving use of total parenteral nutrition in 115 patients with Crohn's disease is reported from a medical unit. Remission occurred without surgery in 24 patients. The regimen was considered to have failed in its objectives in 50 patients, and complications were recorded in 57.

Simultaneous and consecutive administration of nutrients in parenteral nutrition

In seven patients, six with Crohn's disease and one with pancreatitis, two methods of parenteral nutrition were compared: the partial consecutive administration of the components of a parenteral nutrition regimen versus the administration of all nutrients simultaneously. With respect to the consecutive regimen, the simultaneous infusion regimen gave an improvement in the nitrogen balance of 13% and a decrease in urinary lactic acid of about 50%. Urinary excretion of alpha-amino nitrogen, glucose, and fructose was very small in both cases but was slightly lower during the simultaneous infusion regimen. The improvement in the nitrogen balance attained with the simultaneous infusion regimen can be explained by the fact that infused nutrients, especially carbohydrates, cause fewer metabolic disturbances. The simultaneous infusion regimen has three other advantages. The patients rarely complain of headache and nausea, the infusion regimen is markedly simplified and the risk of contamination when nutrients are added to the infusion bottles in the ward is considerably diminished.

Skin lesions in acquired zinc deficiency due to parenteral nutrition

The skin lesions seen in 10 patients who received parenteral nutrition during treatment of chronic enteropathy are described. All of these patients had a lowered serum zinc concentration. The skin lesions were similar to those seen in acrodermatitis enteropathica. After supplementation with zinc sulphate, the skin lesions disappeared completely. A decrease in the serum alkaline phosphatase level can be regarded as a sign of an impending zinc deficiency. Parenteral nutrition formulae should contain a sufficient amount of zinc.