Thiopurine methyltransferase (TPM T) activity exhibits monogenic co-dominant inheritance, with ethnic differences in the frequency of occurrence of variant alleles. With conventional thiopurine doses, homozygous TPMT-deficient patients (~1 in 178 to 1 in 3,736 individuals with two nonfunctional TPMT alleles) experience severe myelosuppression, 30–60% of individuals who are heterozygotes (~3–14% of the population) show moderate toxicity, and homozygous wildtype individuals (~86–97% of the population) show lower active thioguanine nucleolides and less myelosuppression. We provide dosing recommendations (updates at http://www.pharmgkb.org) for azathioprine, mercaptopurine (MP), and thioguanine based on TPMT genotype.

The Clinical Pharmacogenetics Implementation Consortium (CPIC) Guideline for Thiopurine Methyltransferase Genotype and Thiopurine Dosing was originally published in March 2011. We reviewed recent literature and concluded that although relevant new evidence has been generated, none of the evidence would change the primary dosing recommendations in the original guideline; therefore, the original publication remains clinically current. Up‐to‐date information on thiopurine methyltransferase (TPMT) gene alleles and nomenclature can be found at PharmGKB (http://www.pharmgkb.org). Clinical Pharmacology & Therapeutics (2013); 93 4, 324–325. doi:

Inadequate bowel cleansing negatively affects the efficiency of colonoscopy in routine clinical practice. The aim of this study was to design and validate a predictive model for inadequate bowel cleanliness. The model was built from 667 consecutive outpatients (development cohort) who were prospectively scheduled for colonoscopy between June and September 2014. The validation cohort included 409 outpatients who underwent colonoscopy between October and December 2014. Cleansing was evaluated using the Boston Bowel Preparation Scale (BBPS). Bowel preparation was administered on the same day as the examination. In the development cohort, BBPS was adequate in 541 patients (81.1 %). At multivariate analysis, antidepressants (odds ratio [OR] 4.25, 95 % confidence interval [CI] 1.91 - 9.47), co-morbidity (OR 3.35, 95 %CI 2.16 - 5.18), constipation (OR 2.09, 95 %CI 1.29 - 3.40), and abdominal/pelvic surgery (OR 1.60, 95 %CI 1.03 - 2.47) were independent predictors for inadequate cleansing. The model built with these variables showed an area under the curve of 0.72 in the development cohort and 0.70 in the validation cohort. A cutoff of 1.225 predicted inadequate bowel preparation with a sensitivity, specificity, positive predictive value, and negative predictive value of 60.3 % (95 %CI 51.6 - 68.4), 75.4 % (95 %CI 71.6 - 78.9), 36.4 % (95 %CI 30.1 - 43.1), and 89.1 % (95 %CI 85.9 - 91.6) in the development cohort, and 50.0 % (95 %CI 38.1 - 61.9), 80.0 % (95 %CI 75.3 - 84.2), 35.7 % (95 %CI 26.4 - 45.6), and 87.9 % (95 %CI 83.7 - 91.3) in the validation cohort. A simple score may assist the clinician in predicting which patients are at high risk of inadequate bowel cleanliness. This may guide changes in bowel preparation strategy accordingly.

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