Real-World Adherence to and Persistence with Vibegron in Patients with Overactive Bladder: A Retrospective Claims Analysis.

INTRODUCTION: Vibegron is a ß3-adrenergic receptor agonist approved for overactive bladder (OAB). This analysis assessed real-world adherence and persistence with vibegron in patients with OAB, along with demographics and clinical characteristics associated with adherence and persistence. METHODS: This retrospective study used the Optum Research Database to identify patients treated with vibegron from April 2021 to August 2022 (identification period). Patients had ≥ 60 days of continuous pharmacy coverage in a commercial or Medicare Advantage plan following the index fill (follow-up). Adherence was assessed as proportion of days covered (PDC) from index to end of follow-up and was defined as PDC ≥ 80%. Persistence was measured as days to discontinuation of therapy (30-day gap) or end of follow-up. Data for adherence and persistence are presented descriptively. Characteristics associated with adherence and persistence were analyzed using multivariable models among patients with medical and pharmacy benefits during the 90 days before index (baseline). RESULTS: Overall, 9992 patients had a vibegron claim during the identification period; 9712 had ≥ 2 months of follow-up. Mean (SD) age was 74.2 (10.7) years; 68.2% were female. Mean (SD) PDC was 0.64 (0.34). Median (95% confidence interval) persistence was 142 (132-153) days. Of the 5073 patients who were ≥ 18 years old with continuous baseline pharmacy and medical benefits ≥ 90 days before index, 2497 (49.2%) were adherent. Patients were more likely to be adherent and persistent if they received a greater days' supply for the index fill and had baseline medication count ≥ 6. Patients were more likely to discontinue if their index copay was > $45. CONCLUSION: Nearly half of the patients initiating vibegron were adherent. Factors associated with adherence and persistence were more likely to be related to prescribing practices than patient characteristics. These results suggest it may be best to follow up with patients approximately 4 to 5 months after initiating treatment with vibegron.

Vibegron is a newer drug for treating overactive bladder. Vibegron was safe and worked well in clinical trials. However, there is no information on use of vibegron in a real-world population that is not a clinical trial. This study looked at how consistently and how long patients took vibegron after starting it. It also looked at what was common in patients who took vibegron consistently. To do this, the study used pharmacy prescription data from April 2021 to August 2022. It examined adherence to the study medication for each patient. Adherence is how many days patients had medication on hand compared to how long they were followed. The study also looked at persistence to the study medication. Persistence is how long a patient takes a medication before they stop taking it. Researchers then examined if there were reasons a patient may or may not take vibegron as prescribed. The study included prescription data for 9712 patients. The average age was 74 years and 68% of patients were female. Patients had their medication 64% of the time (adherence). On average, patients took their medication for 142 days before stopping (persistence). Patients had better adherence and persistence if they received a larger supply of medication at the pharmacy when first prescribed the medication and if they had more medications overall. Patients' age and gender did not affect adherence and persistence. Vibegron may be a good option for patients with overactive bladder. Follow-up with a provider may be considered 4 to 5 months after starting vibegron.

Surgical Scheduling Impacts Hospital Length of Stay and Associated Healthcare Costs for Patients Undergoing Total Hip and Knee Arthroplasty.

Background: Surgical scheduling, specifically the day of the week on which surgery is performed, has been associated with various postoperative outcomes in patients undergoing lower extremity joint arthroplasty. Purpose: We sought to investigate surgical scheduling as a potential modifiable factor for patient quality metrics and related costs. Methods: In a retrospective prognostic study, all total knee and total hip arthroplasty (TKA/THA) cases that took place in 2017 to 2018 at a multihospital academic health system were queried. Patients were separated by the day of the week the surgery was performed, with Monday/Tuesday compared to Thursday/Friday. Outcomes included length of stay (LOS) (extended LOS defined as 3 days or longer), cost, and complications. Multivariable regression models measured associations between scheduling of surgery and outcomes; odds ratios (OR) and 95% confidence intervals (CIs) are reported. Results: Overall, 1,571 TKA and 992 THA patients were included (65% and 35%, respectively, performed on Monday/Tuesday and 70% and 30%, respectively, performed on Thursday/Friday). Patients undergoing TKA on Monday/Tuesday versus Thursday/Friday had higher American Society of Anesthesiologists scores (42% vs 33% with score of 3 or higher) but less often an extended LOS (31% vs 54%; adjusted OR: 2.76, 95% CI: 2.22-3.46), lower skilled nursing facility costs (unadjusted mean, $12,515 vs $14,154) and lower home health aide costs (unadjusted mean, $3,793 vs $4,192). Similar patterns were observed in THA patients. Conclusion: These results from institutional data suggest that surgical scheduling is a modifiable factor possibly associated with postoperative outcomes. Furthermore, more rigorous study is warranted.

The Impact of Diabetes on Outcomes and Health Care Costs Following Anterior Cervical Discectomy and Fusion.

STUDY DESIGN: Retrospective cohort study. OBJECTIVES: Anterior cervical discectomy and fusion (ACDF) is commonly used to treat an array of cervical spine pathology and is associated with good outcomes and low complication rates. Diabetes mellitus (DM) is a common comorbidity for patients undergoing ACDF, but the literature is equivocal about the impact it has on outcomes. Because DM is a highly prevalent comorbidity, it is crucial to determine if it is an associated risk factor for outcomes after ACDF procedures. METHODS: Patients at a single institution from 2008 to 2016 undergoing ACDF were compared on the basis of having a prior diagnosis of DM versus no DM. The 2 cohorts were compared utilizing univariate tests and multivariate logistic and linear regressions. RESULTS: Data for 2470 patients was analyzed. Diabetic patients had significantly higher Elixhauser scores (P < .0001). Univariate testing showed diabetic patients were more likely to suffer from sepsis (0.82% vs 0.10%, P = .03) and bleeding complications (3.0% vs 1.5%, P = .04). In multivariate analyses, diabetic patients had higher rates of non-home discharge (odds ratio [OR] = 1.37, 95% confidence interval [CI] = 1.07-1.75, P = .013) and prolonged length of stay (OR = 1.95, 95% CI = 1.25-3.05, P = .003), but similar complication (OR = 1.46, 95% CI = 0.85-2.52, P = .17), reoperation (OR = 0.77, 95% CI = 0.33-1.81, P = .55), and 90-day readmission (OR = 1.53, 95% CI = 0.97-2.43) rates compared to nondiabetic patients. Direct cost was also shown to be similar between the cohorts after adjusting for patient, surgical, and hospital-related factors (estimate = -$30.25, 95% CI = -$515.69 to $455.18, P = .90). CONCLUSIONS: Diabetic patients undergoing ACDF had similar complication, reoperation, and readmission rates, as well as similar cost of care compared to nondiabetic patients.

The Cost of Poor Mental Health in Total Joint Arthroplasty.

BACKGROUND: The purpose of this analysis was to evaluate (1) the impact of depression on resource utilization and financial outcomes in bundled total joint arthroplasty (TJA) and (2) whether similar effects are seen using baseline patient-reported outcome scores. METHODS: All elective bundled TJA cases from 2017 to 2018 at an academic system in the New York City area were included. We analyzed variables associated with cost differences seen between patients with and without depression, and between patients with low (<40th percentile) and high baseline (>60th percentile) Veterans RAND 12-Item Health Survey mental component scores (MCSs). We also analyzed whether depression or low MCS could predict worse financial outcomes. RESULTS: Our population included 825 patients, 418 with patient-reported outcome scores data. Depression was associated with higher rates of skilled nursing facility (SNF) discharge (42.7% vs 36.5%, P = .04), SNF payments ($16,200 vs $12,100, P = .0002), and average total episode costs ($31,000 vs $27,000, P = .04). Depression predicted bundle cost to be greater than target price (OR 1.82, 95% CI: 1.04-.16; P = .04) and SNF payment greater than 75th percentile (OR: 1.91; 95% CI: 1.00-3.65; P < .05). Similar effects were not seen using MCS. CONCLUSION: This is the first study to determine that depression predicts bundle cost greater than target price and SNF payment greater than 75th percentile. Our results emphasize the importance of accurate preoperative assessment of mental health in optimization of care, focusing on attenuating the increased SNF payments associated with depression. As similar effects were not seen using MCS, future studies should analyze the use of validated screening tools for depression, such as the PHQ-9, for more accurate assessments of patient mental health in TJA.

Disparities in Outcomes by Insurance Payer Groups for Patients Undergoing Anterior Cervical Discectomy and Fusion.

STUDY DESIGN: Retrospective, observational study of clinical outcomes at a single institution. OBJECTIVE: To compare postoperative complication and readmission rates of payer groups in a cohort of patients undergoing anterior cervical discectomy and fusion (ACDF). SUMMARY OF BACKGROUND DATA: Studies examining associations between primary payer and outcomes in spine surgery have been equivocal. METHODS: Patients at Mount Sinai having undergone ACDF from 2008 to 2016 were queried and assigned to one of five insurance categories: uninsured, managed care, commercial indemnity insurance, Medicare, and Medicaid, with patients in the commercial indemnity group serving as the reference cohort. Multivariable logistic regression equations for various outcomes with the exposure of payer were created, controlling for age, sex, American Society of Anesthesiology Physical Status Classification (ASA Class), the Elixhauser Comorbidity Index, and number of segments fused. A Bonferroni correction was utilized, such that alpha = 0.0125. RESULTS: Two thousand three hundred eighty seven patients underwent ACDF during the time period. Both Medicare (P < 0.0001) and Medicaid (P < 0.0001) patients had higher comorbidity burdens than commercial patients when examining ASA Class. Managed care (2.86 vs. 2.72, P = 0.0009) and Medicare patients (2.99 vs. 2.72, P < 0.0001) had more segments fused on average than commercial patients. Medicaid patients had higher rates of prolonged extubation (odds ratio [OR]: 4.99; 95% confidence interval [CI]: 1.13-22.0; P = 0.007), and Medicare patients had higher rates of prolonged length of stay (LOS) (OR: 2.44, 95% CI: 1.13-5.27%, P = 0.004) than the commercial patients. Medicaid patients had higher rates of 30- (OR: 4.12; 95% CI: 1.43-11.93; P = 0.0009) and 90-day (OR: 3.28; 95% CI: 1.34-8.03; P = 0.0009) Emergency Department (ED) visits than the commercial patients, and managed care patients had higher rates of 30-day readmission (OR: 3.41; 95% CI: 1.00-11.57; P = 0.0123). CONCLUSION: Medicare and Medicaid patients had higher rates of prolonged LOS and postoperative ED visits, respectively, compared with commercial patients. LEVEL OF EVIDENCE: 3.

Defining and Optimizing Value in Total Joint Arthroplasty From the Patient, Payer, and Provider Perspectives.

BACKGROUND: The purpose of this study is to define value in bundled total joint arthroplasty (TJA) from the differing perspectives of the patient, payer/employer, and hospital/provider. METHODS: Demographic, psychosocial, clinical, financial, and patient-reported outcomes (PROs) data from 2017 to 2018 elective TJA cases at a multihospital academic health system were queried. Value was defined as improvement in PROs (preoperatively to 1 year postoperatively) for patients, improvement in PROs per $1000 of bundle cost for payers, and the normalized sum of improvement in PROs and hospital bundle margin for providers. Bivariate analysis was used to compare high value vs low value (>50th percentile vs <50th percentile). Multivariate analysis was performed to identify predictors. RESULTS: A total of 280 patients had PRO data, of which 71 had Medicare claims data. Diabetes (odds ratio [OR], 0.45; P = .02) predicted low value for patients; female gender (OR, 0.25), hypertension (OR, 0.17), pulmonary disease (OR, 0.12), and skilled nursing facility discharge (OR, 0.17) for payers (P ≤ .03 for all); and pulmonary disease (OR, 0.16) and skilled nursing facility discharge (OR, 0.19) for providers (P ≤ .04 for all). CONCLUSION: This is the first article to define value in TJA under a bundle payment model from multiple perspectives, providing a foundation for future studies analyzing value-based TJA.

What Are the Uses and Limitations of Time-driven Activity-based Costing in Total Joint Replacement?

BACKGROUND: With increasing emphasis on value-based payment models for primary total joint arthroplasty (TJA), there is greater need for orthopaedic surgeons and hospitals to better understand the actual costs and resource use of TJA. Time-driven activity-based costing (TDABC) is a methodology for accurate cost estimation, but its application in the TJA care pathway across institutions/regions has not yet been analyzed. QUESTIONS/PURPOSES: In this systematic review of studies applying TDABC to primary TJA, we investigated the following: (1) Is there variation in TDABC methodology and cost estimates across institutions? (2) Is a standard set of direct and indirect costs included across studies? (3) Is there a difference in cost estimates derived from TDABC and traditional hospital cost-accounting approaches? and (4) How are institutions using TDABC (process and outputs) with respect to the TJA care pathway? METHODS: A comprehensive search strategy was developed that included the keywords "TDABC," "time-driven activity-based cost," "THA," "TKA," "THR," "TKR," and "TJR" in the PubMed/MEDLINE, EMBASE, Web of Science, Ovid SP, Scopus, and ScienceDirect databases for articles published between 2004 and 2018 as well as extensive hand searching and citation mining. Relevant studies (n = 15) were screened to include THA or TKA as the focus of the TDABC model, full-text articles, TDABC-based cost estimates for TJA, and studies written in English (n = 8). Due to the heterogeneity of outcomes/methodology in TDABC studies involving TJA, quality assessment was based on each study's adherence to the seven steps delineated by Kaplan et al. in their original publication introducing TDABC in health care. RESULTS: There was substantial variation in TDABC methodology (especially in scope), adherence to the seven steps of TDABC, and data collection. Only five of eight studies incorporated indirect costs into their TDABC calculation, with notable differences in which direct and indirect expenses were included. TDABC-based cost estimates for TJA ranged from USD 7081 to USD 29,557, with variation driven by the TJA timeframe and whether implant costs were included in the costing calculation. TDABC was most frequently used to compare against traditional hospital accounting methods (n = 4), to increase operational efficiency (n = 4), to reduce wasted resources (n = 3), and to mitigate risk (n = 3). CONCLUSIONS: TDABC-based cost estimates are more granular and useful in practice than those calculated via traditional hospital accounting; however, there is a lack of standardized principles to guide TDABC implementation (especially for indirect costs) due to institutional and regional differences in TDABC application. Although TDABC methodology will likely continue to vary somewhat between studies, standardized principles are needed to guide the definition, estimation, and reporting of costs to enable detailed examination of study methodology and inputs by readers. LEVEL OF EVIDENCE: Level III, economic and decision analysis.

Skilled Nursing Facility Placement Process After Total Hip and Total Knee Arthroplasty: Revised Rating System and Opportunities for Intervention.

BACKGROUND: With the advent of bundled payment models, identifying high-performing skilled nursing facilities (SNFs) has become increasingly important. The goal of this study is to develop a rating system to rank SNFs within our health system and to use this system to improve the SNF discharge process at our institution. METHODS: All SNF-discharged primary total joint arthroplasty cases in 2017 at a multi-hospital academic health system were queried. Discharge patterns were assessed using heat map analysis. Regression analyses in conjunction with structured discussions with subject matter experts were used to identify measures of SNF efficiency and care quality. A revised rating system was developed and used to identify high-performing facilities within our health system. Opportunities to re-direct patients to higher performing facilities were identified. RESULTS: A revised rating system for SNFs was constructed based on risk-adjusted SNF length of stay, 30-day re-admission rate, and 30-day emergency department visit rate. As 82% of patients were discharged to SNFs in close proximity to their home, high-performing SNFs (according to the revised rating system) were identified by geographic region. Mapping of the discharge process revealed multiple opportunities where patients could be re-directed to a higher performing SNF in their area. Using conservative estimates (25% of discharges re-directed), this is expected to achieve a cost saving of $2,600,000 over a 5-year period, mainly through reductions in SNF length of stay. CONCLUSION: This study describes the development of a revised rating system for SNFs which, when implemented, is expected to achieve substantial cost savings over a 5-year period.

Preoperative Patient-Reported Outcomes and Clinical Characteristics as Predictors of 90-Day Cost/Utilization and Complications.

BACKGROUND: With the advent of mandatory bundle payments for total joint arthroplasty (TJA), assessing patients' risk for increased 90-day complications and resource utilization is crucial. This study assesses the degree to which preoperative patient-reported outcomes predict 90-day complications, episode costs, and utilization in TJA patients. METHODS: All TJA cases in 2017 at 2 high-volume hospitals were queried. Preoperative HOOS/KOOS JR (Hip Injury and Osteoarthritis Outcome Score/Knee Injury and Osteoarthritis Outcome Score) and Veterans RAND 12-item health survey (VR-12) were administered to patients preoperatively via e-collection platform. For patients enrolled in the Medicare bundle, cost data were extracted from claims. Bivariate and multivariate regression analyses were performed. RESULTS: In total, 2108 patients underwent TJA in 2017; 1182 (56%) were missing patient-reported outcome data and were excluded. The final study population included 926 patients, 199 (21%) of which had available cost data. Patients with high bundle costs tended to be older, suffer from vascular disease and anemia, and have higher Charlson scores (P < .05 for all). These patients also had lower baseline VR-12 Physical Component Summary Score (PCS; 24 vs 30, P ≤ .001) and higher rates of extended length of stay, skilled nursing facility discharge, 90-day complications, and 90-day readmission (P ≤ .04 for all). In multivariate analysis, higher baseline VR-12 PCS was protective against extended length of stay, skilled nursing facility discharge, >75th percentile bundle cost, and 90-day bundle cost exceeding target bundle price (P < .01 for all). Baseline VR-12 Mental Component Summary Score and HOOS/KOOS JR were not predictive of complications or bundle cost. CONCLUSION: Low baseline VR-12 PCS is predictive of high 90-day bundle costs. Baseline HOOS/KOOS JR scores were not predictive of utilization or cost. Neither VR-12 nor HOOS/KOOS JR was predictive of 90-day readmission or complications.

Are Medicare's Nursing Home Compare Ratings Accurate Predictors of 90-Day Complications, Readmission, and Bundle Cost for Patients Undergoing Primary Total Joint Arthroplasty?

BACKGROUND: Nursing Home Compare (NHC) ratings, created and maintained by Medicare, are used by both hospitals and consumers to aid in the skilled nursing facility (SNF) selection process. To date, no studies have linked NHC ratings to actual episode-based outcomes. The purpose of this study was to evaluate whether NHC ratings are valid predictors of 90-day complications, readmission, and bundle costs for patients discharged to an SNF after primary total joint arthroplasty (TJA). METHODS: All SNF-discharged primary TJA cases in 2017 at a multihospital academic health system were queried. Demographic, psychosocial, and clinical variables were manually extracted from the health record. Medicare NHC ratings were then collected for each SNF. For patients in the Medicare bundle, postacute and total bundle cost was extracted from claims. RESULTS: Four hundred eighty-eight patients were discharged to a total of 105 unique SNFs. In multivariate analysis, overall NHC rating was not predictive of 90-day readmission/major complications, >75th percentile postacute cost, or 90-day bundle cost exceeding the target price. SNF health inspection and quality measure ratings were also not predictive of 90-day readmission/major complications or bundle performance. A higher SNF staffing rating was independently associated with a decreased odds for >75th percentile 90-day postacute spend (odds ratio, 0.58; P = .01) and a 90-day bundle cost exceeding the target price (odds ratio = 0.69; P = .02) but was similarly not predictive of 90-day readmission/complications. CONCLUSION: Results of our study suggest that Medicare's NHC tool is not a useful predictor of 90-day costs, complications, or readmissions for SNFs within our health system.

Assessment of owner-administered monthly treatments with oral spinosad or topical spot-on fipronil/(S)-methoprene in controlling fleas and associated pruritus in dogs.

Monitoring of the performance of flea control products under conditions of natural challenge is valuable in assessing continued effectiveness and determining the ongoing relevance of laboratory studies. A multi-clinic, investigator-blinded study was undertaken in client-owned dogs to investigate and compare the flea control provided by 3 consecutive monthly treatments of oral spinosad (SPN) or fipronil/(S)-methoprene topical (FSM) spot-on. The first household dog meeting enrollment criteria and with at least 10 fleas (whole-body flea count) served as the index dog in a household against which primary objectives were set. Stratification was based on pruritus scores at the enrollment visit and on single or multiple pet household. Index pets were randomized to treatment with either SPN or FSM, dispensed on day 0 for at-home administration by owners. All other household dogs and cats, maximum 4 pets per household, were dispensed the same treatment as the index dog (spinetoram was dispensed for cats in SPN households). Subsequent treatments were dispensed when index dogs were returned for whole-body flea counts and pruritus-scoring at visits on days 30 and 60, with final assessments on day 90 (±5 days on each occasion). Primary endpoints were the number of flea-free index dogs in each group one month after the final treatment, the reduction in owner-reported pruritus, and the reduction from baseline mean flea counts. One hundred twenty eight index dogs were enrolled (65 in the SPN arm; 63 in the FSM arm) at 10 clinics in FL (6), NC (2), LA (1), and TX (1). On day 0, geometric mean flea counts were 57.7 (range: 10-1469) and 44.8 (10-717) for the SPN and FSM groups, respectively. On Day 90, 55 of 58 (95%) and 21 of 55 (38%) index dogs completing the study were flea-free in SPN and FSM groups, respectively; mean SPN pruritus scores declined to 0.92 (6.67 on day 0), and to 3.83 (6.33 on day 0) for FSM; geometric mean flea counts (% control) were 0.08 (99.9%) and 5.19 (88.4%), for SPN and FSM groups, respectively. Between-treatment differences were highly statistically significant (p<0.0001). In conclusion, SPN provided reliable flea control in client-owned dogs, regardless of challenge level.

Assessment of the effectiveness of a combination product of spinosad and milbemycin oxime on the prophylaxis of canine heartworm infection.

Three separate randomized, blinded, vehicle-controlled studies were conducted to determine the effectiveness of a single treatment and consecutive monthly treatments of a combination flavored tablet product containing spinosad and milbemycin oxime (MBO) in the prevention of the establishment of heartworm infections in dogs challenged with recent field isolates of the heartworm (HW), Dirofilaria immitis. For each study, dogs were allocated randomly based on pre-treatment body weights to treated or control groups of 10 animals each. Dogs were infected once with infective HW larvae, on Day-30, using either a Michigan isolate or a Georgia (MP3) isolate of D. immitis. Treatments of beef-flavored chewable tablets were administered in two studies one time either on Day 0 or Day 15, and in one study twice (Days 0 and 30, or Days 15 and 45) or 3 times (Days 0, 30 and 60). For the combination product groups, dosages were in the range of 30-45 mg/kg (13.6-20.5mg/lb) for spinosad and 0.5-0.75 mg/kg (0.2-0.34 mg/lb) for MBO. Necropsies for heartworm counts were completed following euthanasia on Day 120 or Day 123. A single treatment with the combination product of spinosad and MBO 30 or 45 days post-inoculation with infective HW larvae was completely effective (100%) in preventing establishment of the Michigan D. immitis isolate, but efficacy against the Georgia MP3 isolate was incomplete, with geometric mean reductions in HW counts relative to vehicle treated controls of 99% reduction of the 30 day infection and a 98.9% reduction of the 45 day old infection. Against this same MP3 isolate, 3 consecutive monthly treatments provided complete prevention (100%) against establishment of D. immitis infections. The combination product of spinosad and MBO provides effective control of canine heartworms. A single treatment at 30 days post infection showed high but incomplete effectiveness against a heartworm isolate that had been shown to be partially refractory to treatment with marketed monthly heartworm preventives. Three consecutive monthly treatments provided complete control, providing support to the recommendation that heartworm prophylaxis should be maintained year round for optimal effectiveness.

Application of a mathematical model to describe the effects of chlorpyrifos on Caenorhabditis elegans development.

BACKGROUND: The nematode Caenorhabditis elegans is being assessed as an alternative model organism as part of an interagency effort to develop better means to test potentially toxic substances. As part of this effort, assays that use the COPAS Biosort flow sorting technology to record optical measurements (time of flight (TOF) and extinction (EXT)) of individual nematodes under various chemical exposure conditions are being developed. A mathematical model has been created that uses Biosort data to quantitatively and qualitatively describe C. elegans growth, and link changes in growth rates to biological events. Chlorpyrifos, an organophosphate pesticide known to cause developmental delays and malformations in mammals, was used as a model toxicant to test the applicability of the growth model for in vivo toxicological testing. METHODOLOGY/PRINCIPAL FINDINGS: L1 larval nematodes were exposed to a range of sub-lethal chlorpyrifos concentrations (0-75 microM) and measured every 12 h. In the absence of toxicant, C. elegans matured from L1s to gravid adults by 60 h. A mathematical model was used to estimate nematode size distributions at various times. Mathematical modeling of the distributions allowed the number of measured nematodes and log(EXT) and log(TOF) growth rates to be estimated. The model revealed three distinct growth phases. The points at which estimated growth rates changed (change points) were constant across the ten chlorpyrifos concentrations. Concentration response curves with respect to several model-estimated quantities (numbers of measured nematodes, mean log(TOF) and log(EXT), growth rates, and time to reach change points) showed a significant decrease in C. elegans growth with increasing chlorpyrifos concentration. CONCLUSIONS: Effects of chlorpyrifos on C. elegans growth and development were mathematically modeled. Statistical tests confirmed a significant concentration effect on several model endpoints. This confirmed that chlorpyrifos affects C. elegans development in a concentration dependent manner. The most noticeable effect on growth occurred during early larval stages: L2 and L3. This study supports the utility of the C. elegans growth assay and mathematical modeling in determining the effects of potentially toxic substances in an alternative model organism using high-throughput technologies.

A discrete time model for the analysis of medium-throughput C. elegans growth data.

BACKGROUND: As part of a program to predict the toxicity of environmental agents on human health using alternative methods, several in vivo high- and medium-throughput assays are being developed that use C. elegans as a model organism. C. elegans-based toxicological assays utilize the COPAS Biosort flow sorting system that can rapidly measure size, extinction (EXT) and time-of-flight (TOF), of individual nematodes. The use of this technology requires the development of mathematical and statistical tools to properly analyze the large volumes of biological data. METHODOLOGY/PRINCIPAL FINDINGS: Findings A Markov model was developed that predicts the growth of populations of C. elegans. The model was developed using observations from a 60 h growth study in which five cohorts of 300 nematodes each were aspirated and measured every 12 h. Frequency distributions of log(EXT) measurements that were made when loading C. elegans L1 larvae into 96 well plates (t = 0 h) were used by the model to predict the frequency distributions of the same set of nematodes when measured at 12 h intervals. The model prediction coincided well with the biological observations confirming the validity of the model. The model was also applied to log(TOF) measurements following an adaptation. The adaptation accounted for variability in TOF measurements associated with potential curling or shortening of the nematodes as they passed through the flow cell of the Biosort. By providing accurate estimates of frequencies of EXT or TOF measurements following varying growth periods, the model was able to estimate growth rates. Best model fits showed that C. elegans did not grow at a constant exponential rate. Growth was best described with three different rates. Microscopic observations indicated that the points where the growth rates changed corresponded to specific developmental events: the L1/L2 molt and the start of oogenesis in young adult C. elegans. CONCLUSIONS: Quantitative analysis of COPAS Biosort measurements of C. elegans growth has been hampered by the lack of a mathematical model. In addition, extraneous matter and the inability to assign specific measurements to specific nematodes made it difficult to estimate growth rates. The present model addresses these problems through a population-based Markov model.