Optimization of vancomycin dosing in very low-birth-weight preterm neonates.

OBJECTIVE: To compare vancomycin serum trough concentrations and 24-hour area under the serum concentration-versus-time curve (AUC24) among very low-birth-weight (VLBW) premature infants before and after implementation of an institution-wide increase in neonatal vancomycin dosing. STUDY DESIGN: We performed a retrospective analysis of vancomycin concentrations among preterm VLBW neonates before (2007-2010) and after (2010-2013) implementation of a new vancomycin dosing protocol consisting of increased vancomycin daily dose and frequency of administration. RESULTS: Neonates weighing < 1,500 g and receiving the new vancomycin dosing regimen had lower rates of undetectable trough concentrations (24 vs. 50%, p = 0.04), higher median trough concentrations (10.8 vs. 5.9 µg/mL, p = 0.003), a higher proportion of goal trough concentrations of 10 to 20 µg/mL (35 vs. 4%, p = 0.005), and a significantly higher vancomycin AUC24 (438 vs. 320 mg·h/L, p = 0.004) compared with historical controls. CONCLUSION: Increasing the vancomycin daily dose and dosing frequency led to an increase in vancomycin trough concentrations and AUC24, and a decrease in the proportion of undetectable (< 5.0 µg/mL) troughs, without an increase in toxicity among VLBW premature neonates.

Is blood pressure reduction a valid surrogate endpoint for stroke prevention? An analysis incorporating a systematic review of randomised controlled trials, a by-trial weighted errors-in-variables regression, the surrogate threshold effect (STE) and the Biomarker-Surrogacy (BioSurrogate) Evaluation Schema (BSES).

BACKGROUND: Blood pressure is considered to be a leading example of a valid surrogate endpoint. The aims of this study were to (i) formally evaluate systolic and diastolic blood pressure reduction as a surrogate endpoint for stroke prevention and (ii) determine what blood pressure reduction would predict a stroke benefit. METHODS: We identified randomised trials of at least six months duration comparing any pharmacologic anti-hypertensive treatment to placebo or no treatment, and reporting baseline blood pressure, on-trial blood pressure, and fatal and non-fatal stroke. Trials with fewer than five strokes in at least one arm were excluded. Errors-in-variables weighted least squares regression modelled the reduction in stroke as a function of systolic blood pressure reduction and diastolic blood pressure reduction respectively. The lower 95% prediction band was used to determine the minimum systolic blood pressure and diastolic blood pressure difference, the surrogate threshold effect (STE), below which there would be no predicted stroke benefit. The STE was used to generate the surrogate threshold effect proportion (STEP), a surrogacy metric, which with the R-squared trial-level association was used to evaluate blood pressure as a surrogate endpoint for stroke using the Biomarker-Surrogacy Evaluation Schema (BSES3). RESULTS: In 18 qualifying trials representing all pharmacologic drug classes of antihypertensives, assuming a reliability coefficient of 0.9, the surrogate threshold effect for a stroke benefit was 7.1 mmHg for systolic blood pressure and 2.4 mmHg for diastolic blood pressure. The trial-level association was 0.41 and 0.64 and the STEP was 66% and 78% for systolic and diastolic blood pressure respectively. The STE and STEP were more robust to measurement error in the independent variable than R-squared trial-level associations. Using the BSES3, assuming a reliability coefficient of 0.9, systolic blood pressure was a B + grade and diastolic blood pressure was an A grade surrogate endpoint for stroke prevention. In comparison, using the same stroke data sets, no STEs could be estimated for cardiovascular (CV) mortality or all-cause mortality reduction, although the STE for CV mortality approached 25 mmHg for systolic blood pressure. CONCLUSIONS: In this report we provide the first surrogate threshold effect (STE) values for systolic and diastolic blood pressure. We suggest the STEs have face and content validity, evidenced by the inclusivity of trial populations, subject populations and pharmacologic intervention populations in their calculation. We propose that the STE and STEP metrics offer another method of evaluating the evidence supporting surrogate endpoints. We demonstrate how surrogacy evaluations are strengthened if formally evaluated within specific-context evaluation frameworks using the Biomarker- Surrogate Evaluation Schema (BSES3), and we discuss the implications of our evaluation of blood pressure on other biomarkers and patient-reported instruments in relation to surrogacy metrics and trial design.

Strengths and weaknesses of renal markers as risk factors and surrogate markers.

The reports of associations between albuminuria and estimated glomerular filtration rate and mortality are a major advance in understanding the progression of renal disease and its sequelae. These findings reinforce the importance of population risk profiling. However, application is limited by validity concerns due to substantial unexplained heterogeneity in many meta-analyses. Application to treatment decisions is premature given insufficient analysis of randomized trials of the association of by-arm differences in laboratory measures and by-arm differences in patient-relevant outcomes.

LDL-cholesterol differences predicted survival benefit in statin trials by the surrogate threshold effect (STE).

OBJECTIVE: We describe a new statistical method called the surrogate threshold effect (STE) that estimates the threshold level of a surrogate needed in a clinical trial to predict a benefit in the target clinical outcome. In this article, we apply this method to the LDL-cholesterol biomarker surrogate and survival benefit-target outcome in statin trials. STUDY DESIGN AND SETTING: We identified randomized trials comparing statin treatment to placebo treatment or no treatment and reporting all-cause and cardiovascular mortality. Trials with fewer than five all-cause deaths in at least one arm were excluded. Multiple regression modeled the reduction in all-cause and cardiovascular mortality as a function of LDL-cholesterol difference. The 95% confidence and 95% prediction bands were calculated and graphed to determine the minimum LDL-cholesterol difference (the surrogate threshold) below which there would be no predicted survival benefit. RESULTS: In 16 qualifying trials, regression analysis yielded an all-cause mortality model whose prediction bands demonstrated no overall survival gain with LDL-cholesterol difference values below 1.5 mmol/L. The cardiovascular mortality model yielded prediction bands that demonstrated no cardiovascular survival benefit with LDL-cholesterol difference values below 1.4 mmol/L. CONCLUSIONS: In a multitrial setting, the STE approach is a promising yet straightforward statistical method for evaluating the surrogate validity of biomarkers.

Definitions and validation criteria for biomarkers and surrogate endpoints: development and testing of a quantitative hierarchical levels of evidence schema.

OBJECTIVE: There are clear advantages to using biomarkers and surrogate endpoints, but concerns about clinical and statistical validity and systematic methods to evaluate these aspects hinder their efficient application. Our objective was to review the literature on biomarkers and surrogates to develop a hierarchical schema that systematically evaluates and ranks the surrogacy status of biomarkers and surrogates; and to obtain feedback from stakeholders. METHODS: After a systematic search of Medline and Embase on biomarkers, surrogate (outcomes, endpoints, markers, indicators), intermediate endpoints, and leading indicators, a quantitative surrogate validation schema was developed and subsequently evaluated at a stakeholder workshop. RESULTS: The search identified several classification schema and definitions. Components of these were incorporated into a new quantitative surrogate validation level of evidence schema that evaluates biomarkers along 4 domains: Target, Study Design, Statistical Strength, and Penalties. Scores derived from 3 domains the Target that the marker is being substituted for, the Design of the (best) evidence, and the Statistical strength are additive. Penalties are then applied if there is serious counterevidence. A total score (0 to 15) determines the level of evidence, with Level 1 the strongest and Level 5 the weakest. It was proposed that the term "surrogate" be restricted to markers attaining Levels 1 or 2 only. Most stakeholders agreed that this operationalization of the National Institutes of Health definitions of biomarker, surrogate endpoint, and clinical endpoint was useful. CONCLUSION: Further development and application of this schema provides incentives and guidance for effective biomarker and surrogate endpoint research, and more efficient drug discovery, development, and approval.

Response rate or time to progression as predictors of survival in trials of metastatic colorectal cancer or non-small-cell lung cancer: a meta-analysis.

BACKGROUND: The duration and cost of cancer clinical trials could be reduced if a surrogate endpoint were used in place of survival. We did a meta-analysis to assess the extent to which two surrogates, tumour response and time to progression, are predictive of mortality in metastatic colorectal cancer and non-small-cell lung cancer. METHODS: Summary data (median time to progression, proportion of patients responding to treatment, and median overall survival) from randomised trials of first-line treatment in colorectal cancer (146 trials) and lung cancer (191 trials) were identified. Data were extracted and analysed by linear regression. We used prediction bands for trials with 250, 500, and 750 patients to identify the surrogate threshold effect that would predict a significant difference in survival. FINDINGS: Response to treatment and time to progression correlated with improvement in survival for both lung cancer (p<0.0001 and p=0.0003, respectively) and colorectal cancer (p<0.0001 for both). To predict a significant survival gain in colorectal cancer trials, an improvement of 20% in the number of patients responding to treatment was required in trials with 750 patients, increasing to 26% in trials with 500 patients and 38% in trials with 250 patients. In lung cancer trials, the same prediction required differences in response of 18% for 750 patients, 21% for 500 patients, and 30% for 250 patients. For time to progression for both cancer types, the incremental gain needed to predict a survival improvement was a median of 1.8 months for trials with 750 patients, 2.2 months for 500 patients, and 3.3 months for 250 patients. INTERPRETATION: Irrespective of trial size, large differences in tumour response rate are needed to predict a significant survival benefit. If surrogates are chosen as the primary endpoint in a clinical trial, time to progression is the preferred measure because more modest and achievable differences are needed for a significant survival benefit. Trials in metastatic lung cancer and colorectal cancer should measure survival as their primary outcome unless the surrogate outcome difference is anticipated to exceed the threshold effect size.

Generic patient self-report and investigator report instruments of therapeutic safety and tolerability.

A patient self-report instrument was designed as a patient event index that maps to a parallel investigator instrument. Event importance (a composite of severity, frequency, and duration) was reported, but attribution was not required. The patient instrument used a checklist but also allowed for spontaneous reporting for new or unusual events. The investigator instrument (also a checklist) includes all events reported by the patient, as well as events such as signs, investigations, and diagnoses that would not generally be known to the patient. Presently, both patient and investigator instruments are to be used alongside current methods of adverse event reporting in clinical trials. The patient instrument would serve as a safety/tolerability index, whereas the investigator instrument would be a fully quantifiable (appropriately weighted), standardized adverse event index. As in many methodological projects in medicine, the overriding problem was the tradeoff between validity (comprehensiveness and accuracy) and feasibility (clarity and short administration time) in instrument development. A summary of pilot studies and results of instrument reliability and validity are presented.

Challenges and progress in adverse event ascertainment and reporting in clinical trials.

Toxicity, safety, and tolerability are integral facets of patient risk/benefit decisions, yet the capacity to define, measure, and compare these aspects is underdeveloped compared to aspects of efficacy. There are many reasons for this, scientific and administrative, but all are surmountable. Probably the greatest primary obstacle is the absence of a measurement instrument designed specifically for this purpose. There are increasing calls from various stakeholders for better evidence, and therefore better ascertainment, in this area, especially in randomized trials, and for these reasons OMERACT began deliberations about these concepts in 1994. A prototype coding instrument (the Rheumatology Common Toxicity Criteria) was developed and discussed at OMERACT 5. In the 2 years before OMERACT 7, a process of concept development and iterative design and testing were conducted to develop a patient self-report and investigator-reported adverse event instruments designed for use in trials at the time of visit. The predominant workload is performed by the patient in a self-report checklist, which is then mapped by the trialist onto a medically sophisticated version. This article presents background on the process of developing a dual adverse event instrument, which was presented and critically discussed in detail at OMERACT 7.

Standardized assessment of adverse events in rheumatology clinical trials: summary of the OMERACT 7 drug safety module update.

A presentation, demonstration, and discussion of recently developed adverse event instruments were the topics for the OMERACT 7 Drug Safety Module. The module began with a plenary introducing the needs and challenges of adverse event ascertainment. It was followed by a review of module work from previous OMERACT meetings on a prototype coding instrument (Rheumatology Common Toxicity Criteria), then a brief description of the process behind the recently developed patient self-report and investigator report adverse event instruments. These current instruments are designed for use in controlled trials although they could be used in other settings. The instruments rely primarily on patient self-reporting using a checklist, which the investigator then folds into a parallel structured but more medically sophisticated instrument. In pilot testing, this innovative dual-use system has shown reliability and acceptability, while preserving validity. A "stakeholder panel" of representatives from 8 sectors followed--patient, nurse investigator, regulator, clinician scientist, industry, OMERACT, global public health/WHO, and Cochrane Collaboration--for their perspectives on the needs, challenges, and potential ways forward for adverse event ascertainment and reporting in clinical trials. At the breakout session small focus groups participated in hands-on interactive testing of one of 3 versions of the instruments, which differ in degree of comprehensiveness. Each focus group had a participatory patient with rheumatoid arthritis. At a second plenary there was group feedback by rapporteurs and presentation of results from pilot studies of iterative testing of validity, reliability, and feasibility of the instruments. During plenary discussion a frequent suggestion for improvement was to refine the process so that event ascertainment could be done entirely using the patient instrument with minimal input from the investigator at the visit, if patient-investigator agreement was high. Most found the patient checklist attractive, particularly if the patient instrument was shown to be reliable and valid. Finally, a future research agenda was discussed.

Minimal disease activity for rheumatoid arthritis: a preliminary definition.

Agreement on response criteria in rheumatoid arthritis (RA) has allowed better standardization and interpretation of clinical trial reports. With recent advances in therapy, the proportion of patients achieving a satisfactory state of minimal disease activity (MDA) is becoming a more important measure with which to compare different treatment strategies. The threshold for MDA is between high disease activity and remission and, by definition, anyone in remission will also be in MDA. True remission is still rare in RA; in addition, the American College of Rheumatology definition is difficult to apply in the context of trials. Participants at OMERACT 6 in 2002 agreed on a conceptual definition of minimal disease activity (MDA): "that state of disease activity deemed a useful target of treatment by both the patient and the physician, given current treatment possibilities and limitations." To prepare for a preliminary operational definition of MDA for use in clinical trials, we asked rheumatologists to assess 60 patient profiles describing real RA patients seen in routine clinical practice. Based on their responses, several candidate definitions for MDA were designed and discussed at the OMERACT 7 in 2004. Feedback from participants and additional on-site analyses in a cross-sectional database allowed the formulation of 2 preliminary, equivalent definitions of MDA: one based on the Disease Activity Score 28 (DAS28) index, and one based on meeting cutpoints in 5 out the 7 WHO/ILAR core set measures. Researchers applying these definitions first need to choose whether to use the DAS28 or the core set definition, because although each selects a similar proportion in a population, these are not always the same patients. In both MDA definitions, an initial decision node places all patients in MDA who have a tender joint count of 0 and a swollen joint count of 0, and an erythrocyte sedimentation rate (ESR) no greater than 10 mm. If this condition is not met: * The DAS28 definition places patients in MDA when DAS28 < or = 2.85; * The core set definition places patients in MDA when they meet 5 of 7 criteria: (1) Pain (0-10) < or = 2; (2) Swollen joint count (0-28) < or = 1; (3) Tender joint count (0-28) < or = 1; (4) Health Assessment Questionnaire (HAQ, 0-3) < or = 0.5; (5) Physician global assessment of disease activity (0-10) < or = 1.5; (6) Patient global assessment of disease activity (0-10) < or = 2; (7) ESR < or = 20. This set of 2 definitions gained approval of 73% of the attendees. These (and other) definitions will now be subject to further validation in other databases.