Stratified analysis in comparative effectiveness studies that emulate randomized trials.

PURPOSE: For observational cohort studies that employ matching by propensity scores (PS), preliminary stratification by consequential predictors of outcome better emulates stratified randomization and potentially reduces variance and bias through relaxed dependence on modeling assumptions. We assessed the impact of pre-stratification in two real-life examples. For both, prior evidence from placebo-controlled randomized clinical trials (RCTs) suggested small or no risk reduction, but observational analysis suggested protection, presumably the result of confounding bias. STUDY DESIGN AND SETTING: The study populations consisted of Medicare beneficiaries (2014-18) with type 2 diabetes initiating either (i) empagliflozin versus dipeptidyl peptidase-4 inhibitors (DPP-4i) or (ii) empagliflozin versus glucagon-like peptide-1 receptor agonists (GLP-1RA). The outcome was myocardial infarction or stroke. We estimated hazard ratios (HR) and rate differences (RD) after controlling for 143 pre-exposure covariates via 1:1 PS matching after (1) PS estimation in the total cohort (total-cohort PS-matching) and (2) PS estimation separately by baseline cardiovascular disease (stratified PS matching). RESULTS: Stratified PS matching resulted in HRs that exceeded those from total-cohort PS-matching by 13% and 9%, respectively, for the comparisons of empagliflozin to DPP-4i and GLP-1RA. Against both comparators, HRs and RDs after stratified PS matching were closer to the null, with slightly higher variances (2%-3%) than those after total-cohort PS matching. CONCLUSION: Stratified PS matching produced effect estimates closer to the expected trial findings than total-cohort PS matching. The price paid in increased variance was minimal.

Semiparametric Allocation of Subjects to Cohort Strata.

BACKGROUND: We illustrate a method for stratum assignment in small cohort studies that avoids modeling assumptions. METHODS: Off-the-shelf software ( rgenoud ) made stratum assignments to minimize a loss function built on within-stratum and population-adjusted Euclidean distances. RESULTS: In 100 trials using simulated data of 300 records with a binary treatment and four dissimilar covariate treatment predictors, minimizing a loss based on Euclidean distance reduced covariate imbalance by a median of 99%. Stratification by propensity score and weighting records by the inverse of their probability of treatment reduced imbalance by 76%-89% and 83%-94%, respectively. Loss minimization applied to a cohort of 361 children undergoing immunotherapy achieved nearly complete elimination of covariate differences for important treatment predictors. CONCLUSION: With the availability of semiparametric stratum-assignment algorithms, analysts can tailor loss functions to meet design goals. Here, a loss function that emphasized covariate balance performed well under limited testing.

Antibiotic prescribing patterns among patients admitted to an academic teaching hospital for COVID-19 during the first wave of the pandemic in Toronto: A retrospective, controlled study.

BACKGROUND: Empirical antibiotics are not recommended for coronavirus disease 2019 (COVID-19). METHODS: In this retrospective study, patients admitted to Toronto General Hospital's general internal medicine from the emergency department for COVID-19 between March 1 and August 31, 2020 were compared with those admitted for community-acquired pneumonia (CAP) in 2020 and 2019 in the same months. The primary outcome was antibiotics use pattern: prevalence and concordance with COVID-19 or CAP guidelines. The secondary outcome was antibiotic consumption in days of therapy (DOT)/100 patient-days. We extracted data from electronic medical records. We used logistic regression to model the association between disease and receipt of antibiotics, linear regression to compare DOT. RESULTS: The COVID-19, CAP 2020, and CAP 2019 groups had 67, 73, and 120 patients, respectively. Median age was 71 years; 58.5% were male. Prevalence of antibiotic use was 70.2%, 97.3%, and 90.8% for COVID-19, CAP 2020, and CAP 2019, respectively. Compared with CAP 2019, the adjusted odds ratio (aOR) for receiving antibiotics was 0.23 (95% CI 0.10 to 0.53, p = 0.001) and 3.42 (95% CI 0.73 to 15.95, p = 0.117) for COVID-19 and CAP 2020, respectively. Among patients receiving antibiotics within 48 hours of admission, compared with CAP 2019, the aOR for guideline-concordant combination regimens was 2.28 (95% CI 1.08 to 4.83, p = 0.031) for COVID-19, and 1.06 (95% CI 0.55 to 2.05, p = 0.856) for CAP 2020. Difference in mean DOT/100 patient-days was -24.29 (p = 0.009) comparing COVID-19 with CAP 2019, and +28.56 (p = 0.003) comparing CAP 2020 with CAP 2019. CONCLUSIONS: There are opportunities for antimicrobial stewardship to address unnecessary antibiotic use.

HISTORIQUE: L'antibiothérapie empirique n'est pas recommandée pour le traitement de la maladie à coronavirus 2019 (COVID-19). MÉTHODOLOGIE: Dans cette étude rétrospective, les chercheurs ont comparé les patients atteints de COVID-19 hospitalisés au département de médecine interne générale du Toronto General Hospital entre le 1er mars et le 31 août 2020 après être passés par l'urgence à ceux hospitalisés à cause d'une pneumonie d'origine communautaire (POC) au cours des mêmes mois en 2020 et 2019 (POC-20 et POC-19). Le résultat primaire était le schéma d'utilisation des antibiotiques, c'est-à-dire la prévalence et le respect des lignes directrices sur la COVID-19 ou la POC. Le résultat secondaire correspondait à la consommation d'antibiotiques pendant les jours de traitement (JdT)/100 jours-patients. Les chercheurs ont puisé les données dans les dossiers médicaux électroniques. Ils se sont servi de la régression logistique pour modéliser l'association entre la maladie et la réception des antibiotiques, et de la régression linéaire pour comparer les JdT. RÉSULTATS: Le groupe COVID-19, le groupe POC-20 et le groupe POC-19 étaient composés de 67, 73 et 120 patients, respectivement. Ils avaient un âge médian de 71 ans, et 58,5 % étaient de sexe masculin. La prévalence d'utilisation d'antibiotiques s'élevait à 70,2 %, 97,3 % et 90,8 % dans les groupes COVID-19, POC-20 et POC-19, respectivement. Par rapport au groupe POC-19, le rapport de cotes rajusté (RCr) relatif à la réception d'antibiotiques s'élevait à 0,23 (IC à 95 %, 0,10 à 0,53, p = 0,001) et 3,42 (IC à 95 %, 0,73 à 15,95, p = 0,117) dans les groupes COVID-19 et POC-20, respectivement. Chez les patients qui avaient reçu des antibiotiques dans les 48 heures suivant leur hospitalisation par rapport au POC-19, le RCr relatif à la posologie d'association conforme aux lignes directrices était de 2,28 (IC à 95 %, 1,08 à 4,83, p = 0,031) et de 1,06 (IC à 95 %, 0,55 à 2,05, p = 0,856) dans le groupe POC-20. La différence quant au nombre moyen de JdT/100 jours-patients correspondait à ­24,29 (p = 0,009) lorsqu'on comparait le groupe COVID-19 au groupe POC-19, et à +28,56 (p = 0,003) lorsqu'on comparait le groupe POC-20 au groupe POC-19. CONCLUSIONS: L'utilisation inutile d'antibiotiques pourrait très bien être prise en charge par la gérance des antimicrobiens.

The acute effects of azithromycin use on cardiovascular mortality as compared with amoxicillin-clavulanate in US Veterans.

PURPOSE: Azithromycin is a common first-line antibiotic for respiratory infection; however, there is conflicting evidence regarding risk of cardiovascular death. We assessed cardiovascular and noncardiovascular mortality associated with azithromycin versus amoxicillin-clavulanate among US Veterans treated for nonear-nose-throat respiratory infection ("respiratory") or ear-nose-throat infection indication. METHODS: Electronic health record data from the US Veterans Health Administration database were used to identify Veterans (30-74 years) with outpatient dispensings of oral azithromycin versus amoxicillin-clavulanate for respiratory or ear-nose-throat infection (January 01, 2000-December 31, 2014). Outcomes assessed were risk of cardiovascular death and noncardiovascular death within 1-5 and 6-10 days postdispensing. Inverse probability of treatment-weighted proportional hazards models and binomial regression models were used to estimate hazard ratios (HRs) and compute risk differences (RD) per million courses of therapy. Cardiac death (subset of cardiovascular death) was assessed in sensitivity analyses. RESULTS: There were 629 345 azithromycin and 168 429 amoxicillin-clavulanate dispensings for respiratory indications, 143 783 azithromycin, and 203 142 amoxicillin-clavulanate dispensings for ear-nose-throat indications. For respiratory indications, azithromycin was not associated with a significantly different risk of cardiovascular death versus amoxicillin-clavulanate within 1-5 days postdispensing (HR [95% confidence interval (CI)]: 1.12 [0.63, 2.00]; RD [95% CI]: 11 [-43, 64] deaths/million courses of therapy). No elevated risk for azithromycin was found for ear-nose-throat indications. Pooled results for both indications via meta-analysis showed no association between antibiotics and cardiovascular mortality. There was no significant difference in risk of noncardiovascular or cardiac death between antibiotics postdispensing. CONCLUSION: Azithromycin was not associated with elevated risk of cardiovascular or noncardiovascular death versus amoxicillin-clavulanate among US Veterans.

An Evaluation of the Effect of the OxyContin Reformulation on Unintentional Fatal and Nonfatal Overdose.

OBJECTIVES: OxyContin was reformulated with a polyethylene oxide matrix in August 2010 to reduce the potential for intravenous abuse and for abuse by insufflation. The objective of this study was to evaluate the impact of OxyContin's reformulation on overdose (OD) risk for individuals dispensed OxyContin in comparison to those dispensed other opioids under regular care. MATERIALS AND METHODS: Three national insurance databases with National Death Index linkage identified OD in individuals with any dispensing of OxyContin or a primary comparator opioid (extended release morphine, transdermal fentanyl, or methadone) between July 2008 through September 2015. A difference-in-differences design was used to compare the pre-post reformulation changes in OD rates for OxyContin versus comparators. RESULTS: A total of 297,836 individuals were dispensed OxyContin and 659,673 individuals were dispensed a primary comparator across the 3 databases. Overall, there was little or no difference in the temporal change in OD incidence in comparators versus OxyContin (Medicaid: adjusted ratio-of-rate-ratios (aRoRs) ranging from 0.90 to 1.05; MarketScan/HIRD: aRoR ranging from 1.10 to 1.22). However, restriction to person-time without concomitant opioid use revealed a modestly greater reduction in OD incidence over time during OxyContin use, as the aRoRs comparing the primary comparators to OxyContin ranged from 1.06 to 1.30 in Medicaid and from 1.64 to 1.85 in MarketScan/HIRD. DISCUSSION: This study did not detect an overall effect of the OxyContin reformulation on OD in insured patients under regular medical care. There is a suggestion of a modestly reduced OxyContin-associated OD risk following the reformulation but only in commercially insured individuals receiving single-opioid regimens.

Long-term risk of hepatocellular carcinoma mortality in 23220 hospitalized patients treated with micafungin or other parenteral antifungals.

BACKGROUND: Liver tumours observed in rats exposed to micafungin led to a black box warning upon approval in Europe in 2008. Micafungin's risk for liver carcinogenicity in humans has not been investigated. We sought to describe the risk of fatal hepatocellular carcinoma (HCC) among persons who received micafungin and other parenteral antifungals (PAFs) with up to 12 years of follow-up. METHODS: We assembled a US multicentre cohort of hospitalized patients who received micafungin or other PAFs between 2005 and 2012. We used propensity score (PS) matching on patient characteristics from electronic medical records to compare rates of HCC mortality identified through the National Death Index though to the end of December 2016. We computed HRs and 95% CIs. RESULTS: A total of 40110 patients who received a PAF were identified; 6903 micafungin recipients (87% of those identified) were successfully matched to 16317 comparator PAF users. Ten incident HCC deaths, one in the micafungin-exposed group and nine among comparator PAF users, occurred in 71285 person-years of follow-up. The HCC mortality rate was 0.05 per 1000 person-years in micafungin patients and 0.17 per 1000 person-years in comparator PAF patients. The PS-matched HR for micafungin versus comparator PAF was 0.29 (95% CI 0.04-2.24). CONCLUSIONS: Both micafungin and comparator PAFs were associated with HCC mortality rates of <0.2 per 1000 person-years. Given the very low event rates, any potential risk for HCC should not play a role in clinical decisions regarding treatment with micafungin or other PAFs investigated in this study.

Information on doctor and pharmacy shopping for opioids adds little to the identification of presumptive opioid abuse disorders in health insurance claims data.

BACKGROUND: Doctor and pharmacy shopping ("Shopping") for opioids is related to opioid abuse and is associated with opioid overdose and death. Lacking identifiers for prescribers and pharmacies, many data resources (notably the US FDA's Sentinel System) cannot evaluate Shopping. We used data in which presumptive Shopping could be identified. We investigated whether US health insurance claims data could perform as well as Shopping to identify people with evidence for opioid abuse. METHODS: In this cross-sectional study, we examined health insurance claims from 164,923 persons with at least two dispensing of opioids in 18 months, the first occurring in 2012. Evidence for the presence of a possible opioid abuse disorder was drawn from predictive patterns of drug fills, diagnoses and care-seeking identified in a companion research project, and Shopping was determined using a published index. The prevalence of presumptive opioid abuse was examined across levels of Shopping. The comparison between Shopping and insurance-claims-derived covariates in the detection of apparent opioid abuse was examined in multiple regression analyses. RESULTS: Despite a strong correlation between presumptive opioid abuse and Shopping, most persons with extensive Shopping did not manifest presumptive opioid abuse, and half of the population with presumptive opioid abuse did not exhibit Shopping. As Shopping ranged from "None" to "Extensive," the prevalence of presumptive opioid abuse increased from 0.28 to 5.0 per 100. The discriminating power of Shopping for identifying opioid abuse could be replaced using insurance claims data. CONCLUSION: The results suggest that patient characteristics that can be inferred from insurance claims data provide as complete discrimination of persons with presumptive opioid abuse as does a full assessment of doctor and pharmacy shopping. The inference rests on patterns of health services and drug dispensing that are indicative of doctor-pharmacy shopping and of opioid abuse. There was no direct evaluation of patients. The extent to which the conclusions are generalizable beyond the study population - Americans with health insurance coverage in the early part of this decade - is uncertain in a quantitative sense. The qualitative conclusion is that diagnostic data in health insurance databases can be predictive of behaviors consistent with opioid abuse and that more elaborate indices such as doctor and pharmacy shopping may add little.Registration: ClinicalTrials.gov study number: NCT02668549.

Structural and Functional Characterization of Dynamic Oligomerization in Burkholderia cenocepacia HMG-CoA Reductase.

The enzyme 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase (HMGR), in most organisms, catalyzes the four-electron reduction of the thioester (S)-HMG-CoA to the primary alcohol (R)-mevalonate, utilizing NADPH as the hydride donor. In some organisms, including the opportunistic lung pathogen Burkholderia cenocepacia, it catalyzes the reverse reaction, utilizing NAD+ as a hydride acceptor in the oxidation of mevalonate. B. cenocepacia HMGR has been previously shown to exist as an ensemble of multiple non-additive oligomeric states, each with different levels of enzymatic activity, suggesting that the enzyme exhibits characteristics of the morpheein model of allostery. We have characterized a number of factors, including pH, substrate concentration, and enzyme concentration, that modulate the structural transitions that influence the interconversion among the multiple oligomers. We have also determined the crystal structure of B. cenocepacia HMGR in the hexameric state bound to coenzyme A and ADP. This hexameric assembly provides important clues about how the transition among oligomers might occur, and why B. cenocepacia HMGR, unique among characterized HMGRs, exhibits morpheein-like behavior.

Conditional power for assessing population interventions.

AIM: To calculate conditional power in comparative two-period studies with previously observed baseline data. METHOD: Isolate the variability attributable to the yet-to-observed data and modify the standard power formulae. RESULTS: For illustration, we examine rates of opioid overdose before and after a reformulation of one opioid product. The null hypothesis posited no impact of the reformulation, alternative hypotheses posited possible impacts, and ancillary hypotheses posited different secular pre-post changes directly observable in comparators. Conditional power varied with the size of the comparator population and with the assumed pre-post change for the comparator. CONCLUSION: Pre-post designs can be initiated after the baseline period is over. Power calculations that are conditioned on observed baseline data account differently for variability in the baseline and follow-up periods.

Removal of ineligible outcome cases reduces confounding.

BACKGROUND: When an exclusionary criterion is an imperfect screen, some ineligible patients will remain in a study. Medical record review for outcome adjudication can reveal such individuals. OBJECTIVE: To ascertain the circumstances under which it is advisable to remove outcome cases first found to be ineligible on chart review. METHODS: The impact on the relative risk caused by removal of ineligible outcome cases was examined under different circumstances of confounding, prevalence, and efficacy of the screening criterion for exclusions. The result is illustrated by a hospital-based cohort study in which electronic medical record diagnosis served to exclude ineligible cases, and review of text notes for putative outcome cases revealed that the codes were only 95% sensitive. Other hypothetical scenarios provide further evidence. RESULTS: If a condition to be excluded is a confounder of the exposure-outcome relation, residual confounding will continue to bias a study after application of an imperfect screening criterion. Removal of ineligible outcome cases after chart review creates a new bias, distinct from residual confounding. The new bias does not depend on the magnitude of the confounder-outcome association, and will be small if the exclusion criterion has resulted in a low prevalence of the exclusionary condition. The new bias caused by removal of ineligible outcome cases is almost certain to be smaller than the confounding bias that can result if they are retained. CONCLUSIONS: Outcome cases first discovered at chart review to be study-ineligible should be removed from the study, even when similar scrutiny is infeasible for non-cases.

The Enzyme Activity and Substrate Specificity of Two Major Cinnamyl Alcohol Dehydrogenases in Sorghum (Sorghum bicolor), SbCAD2 and SbCAD4.

Cinnamyl alcohol dehydrogenase (CAD) catalyzes the final step in monolignol biosynthesis, reducing sinapaldehyde, coniferaldehyde, and p-coumaraldehyde to their corresponding alcohols in an NADPH-dependent manner. Because of its terminal location in monolignol biosynthesis, the variation in substrate specificity and activity of CAD can result in significant changes in overall composition and amount of lignin. Our in-depth characterization of two major CAD isoforms, SbCAD2 (Brown midrib 6 [bmr6]) and SbCAD4, in lignifying tissues of sorghum (Sorghum bicolor), a strategic plant for generating renewable chemicals and fuels, indicates their similarity in both structure and activity to Arabidopsis (Arabidopsis thaliana) CAD5 and Populus tremuloides sinapyl alcohol dehydrogenase, respectively. This first crystal structure of a monocot CAD combined with enzyme kinetic data and a catalytic model supported by site-directed mutagenesis allows full comparison with dicot CADs and elucidates the potential signature sequence for their substrate specificity and activity. The L119W/G301F-SbCAD4 double mutant displayed its substrate preference in the order coniferaldehyde > p-coumaraldehyde > sinapaldehyde, with higher catalytic efficiency than that of both wild-type SbCAD4 and SbCAD2. As SbCAD4 is the only major CAD isoform in bmr6 mutants, replacing SbCAD4 with L119W/G301F-SbCAD4 in bmr6 plants could produce a phenotype that is more amenable to biomass processing.

Possible Opioid Shopping and its Correlates.

BACKGROUND: We created an operational definition of possible opioid shopping in US commercial health insurance data and examined its correlates. METHODS: The population consisted of 264,204 treatment courses in persons with a fill for an opioid or diuretic prescription in 2012 and a second within 18 months. We examined counts of prescribers and pharmacies and the numbers of fills and overlaps for ability to discriminate courses of opioids from diuretics, which were a negative control. The most discriminatory measure, indicating possible shopping behavior, was cross-tabulated against other prescriptions filled and diagnoses as found in insurance claims. The associations between claims characteristics and shopping behavior were assessed in a logistic regression. RESULTS: A definition that classified possible "moderate" or "extensive" shopping when a person obtained drug through at least 3 practices and at least 3 pharmacies over 18 months was highly discriminatory between opioid and diuretic treatment. Overlaps between fills and number of fills did not improve the discrimination. Data from insurance claims strongly predicted moderate-to-extensive levels of possible shopping (c=0.82). Prominent among 20 significant predictors were: state of residence; amount of opioid dispensed; self-payment; use of nonspecialist prescribers; high use of anxiolytics, hypnotics, psychostimulants, and antipsychotics; and use of both immediate release and extended-release or long-acting opioids. CONCLUSIONS: The use of ≥3 prescribing practices and ≥3 dispensing pharmacies over 18 months sharply discriminated courses of opioid treatment from courses of diuretics. This pattern of fills was additionally associated with the numbers of nonspecialist and self-paid fills, the total morphine milligram equivalents dispensed, and heavier use of drugs for anxiety, sleep, attention, and psychosis.

Structural and Biochemical Characterization of Cinnamoyl-CoA Reductases.

Cinnamoyl-coenzyme A reductase (CCR) catalyzes the reduction of hydroxycinnamoyl-coenzyme A (CoA) esters using NADPH to produce hydroxycinnamyl aldehyde precursors in lignin synthesis. The catalytic mechanism and substrate specificity of cinnamoyl-CoA reductases from sorghum (Sorghum bicolor), a strategic plant for bioenergy production, were deduced from crystal structures, site-directed mutagenesis, and kinetic and thermodynamic analyses. Although SbCCR1 displayed higher affinity for caffeoyl-CoA or p-coumaroyl-CoA than for feruloyl-CoA, the enzyme showed significantly higher activity for the latter substrate. Through molecular docking and comparisons between the crystal structures of the Vitis vinifera dihydroflavonol reductase and SbCCR1, residues threonine-154 and tyrosine-310 were pinpointed as being involved in binding CoA-conjugated phenylpropanoids. Threonine-154 of SbCCR1 and other CCRs likely confers strong substrate specificity for feruloyl-CoA over other cinnamoyl-CoA thioesters, and the T154Y mutation in SbCCR1 led to broader substrate specificity and faster turnover. Through data mining using our structural and biochemical information, four additional putative CCR genes were discovered from sorghum genomic data. One of these, SbCCR2, displayed greater activity toward p-coumaroyl-CoA than did SbCCR1, which could imply a role in the synthesis of defense-related lignin. Taken together, these findings provide knowledge about critical residues and substrate preference among CCRs and provide, to our knowledge, the first three-dimensional structure information for a CCR from a monocot species.

Short-term risk of liver and renal injury in hospitalized patients using micafungin: a multicentre cohort study.

BACKGROUND: Although echinocandins are generally well tolerated, there is little information on the frequency with which renal and hepatic adverse effects occur during use of micafungin or other parenteral antifungal (PAF) agents in clinical practice. METHODS: MYCOS is a multicentre cohort study of adult and paediatric patients who received micafungin or other PAFs between 2005 and 2012 at seven tertiary care hospitals from six centres in the USA. PAF cohort controls were selected through propensity score (PS) matching to micafungin recipients using clinical characteristics, other treatments, procedures and hospital service where PAF treatment was initiated. Analysis was restricted to patients without chronic liver and kidney conditions at the time of cohort entry. Treatment-emergent hepatic and renal injury was documented by changes in liver enzymes or estimated glomerular filtration rate through 30 days following completion of PAF treatment. Comparisons were quantified using the HR from a proportional hazards analysis. RESULTS: There were 2970 micafungin recipients PS matched to 6726 recipients of comparator PAFs. Balance was achieved in all baseline covariates between treatment groups. There were similar rates of hepatic injury (micafungin, 13 events per 100 patients and other PAF, 12 per 100; HR = 0.99; 95% CI 0.86-1.14) and lower rates of renal injury (micafungin, 63 events per 100 patients and other PAF, 65 per 100; HR = 0.93; 95% CI 0.87-0.99) for micafungin recipients versus PAF comparators. CONCLUSION: For a wide spectrum of underlying conditions, we observed no increase in liver injury by micafungin and possibly a reduced risk of renal dysfunction in comparison with other PAF medications.

Design and analysis choices for safety surveillance evaluations need to be tuned to the specifics of the hypothesized drug-outcome association.

BACKGROUND: We reviewed the results of the Observational Medical Outcomes Research Partnership (OMOP) 2010 Experiment in hopes of finding examples where apparently well-designed drug studies repeatedly produce anomalous findings. OMOP had applied thousands of designs and design parameters to 53 drug-outcome pairs across 10 electronic data resources. Our intent was to use this repository to elucidate some sources of error in observational studies. METHOD: From the 2010 OMOP Experiment, we sought drug-outcome-method combinations (DOMCs) that met consensus design criteria, yet repeatedly produced results contrary to expectation. We set aside DOMCs for which we could not agree on the suitability of the designs, then selected for an in-depth scrutiny one drug-outcome pair analyzed by a seemingly plausible methodological approach, whose results consistently disagreed with the a priori expectation. RESULTS: The OMOP "all-by-all" assessment of possible DOMCs yielded many combinations that would not be chosen by researchers as actual study options. Among those that passed a first level of scrutiny, two of seven drug-outcome pairs for which there were plausible research designs had anomalous results. The use of benzodiazepines was unexpectedly associated with acute renal failure and upper gastrointestinal bleeding. We chose the latter as an example for in-depth study. The factitious appearance of a bleeding risk may have been partly driven by an excess of procedures on the first day of treatment. A risk window definition that excluded the first day largely removed the spurious association. CONCLUSION: One cause of reproducible "error" may be repeated failure to tie design choices closely enough to the research question at hand. Copyright © 2016 John Wiley & Sons, Ltd.

The Structure and Catalytic Mechanism of Sorghum bicolor Caffeoyl-CoA O-Methyltransferase.

Caffeoyl-coenzyme A 3-O-methyltransferase (CCoAOMT) is an S-adenosyl methionine (SAM)-dependent O-methyltransferase responsible for methylation of the meta-hydroxyl group of caffeoyl-coenzyme A (CoA) on the pathway to monolignols, with their ring methoxylation status characteristic of guaiacyl or syringyl units in lignin. In order to better understand the unique class of type 2 O-methyltransferases from monocots, we have characterized CCoAOMT from sorghum (Sorghum bicolor; SbCCoAOMT), including the SAM binary complex crystal structure and steady-state enzyme kinetics. Key amino acid residues were validated with site-directed mutagenesis. Isothermal titration calorimetry data indicated a sequential binding mechanism for SbCCoAOMT, wherein SAM binds prior to caffeoyl-CoA, and the enzyme showed allosteric behavior with respect to it. 5-Hydroxyferuloyl-CoA was not a substrate for SbCCoAOMT. We propose a catalytic mechanism in which lysine-180 acts as a catalytic base and deprotonates the reactive hydroxyl group of caffeoyl-CoA. This deprotonation is facilitated by the coordination of the reactive hydroxyl group by Ca(2+) in the active site, lowering the pKa of the 3'-OH group. Collectively, these data give a new perspective on the catalytic mechanism of CCoAOMTs and provide a basis for the functional diversity exhibited by type 2 plant OMTs that contain a unique insertion loop (residues 208-231) conferring affinity for phenylpropanoid-CoA thioesters. The structural model of SbCCoAOMT can serve as the basis for protein engineering approaches to enhance the nutritional, agronomic, and industrially relevant properties of sorghum.

Computer-assisted expert case definition in electronic health records.

PURPOSE: To describe how computer-assisted presentation of case data can lead experts to infer machine-implementable rules for case definition in electronic health records. As an illustration the technique has been applied to obtain a definition of acute liver dysfunction (ALD) in persons with inflammatory bowel disease (IBD). METHODS: The technique consists of repeatedly sampling new batches of case candidates from an enriched pool of persons meeting presumed minimal inclusion criteria, classifying the candidates by a machine-implementable candidate rule and by a human expert, and then updating the rule so that it captures new distinctions introduced by the expert. Iteration continues until an update results in an acceptably small number of changes to form a final case definition. RESULTS: The technique was applied to structured data and terms derived by natural language processing from text records in 29,336 adults with IBD. Over three rounds the technique led to rules with increasing predictive value, as the experts identified exceptions, and increasing sensitivity, as the experts identified missing inclusion criteria. In the final rule inclusion and exclusion terms were often keyed to an ALD onset date. When compared against clinical review in an independent test round, the derived final case definition had a sensitivity of 92% and a positive predictive value of 79%. CONCLUSION: An iterative technique of machine-supported expert review can yield a case definition that accommodates available data, incorporates pre-existing medical knowledge, is transparent and is open to continuous improvement. The expert updates to rules may be informative in themselves. In this limited setting, the final case definition for ALD performed better than previous, published attempts using expert definitions.