Antimicrobial resistance patterns and empiric antibiotic selections for patients admitted from post-acute care facilities

PURPOSE

To characterize the susceptibilities of positive bacterial cultures and the appropriateness of empiric antimicrobial regimens for patients admitted from post-acute care facilities (PACFs).

METHODS

This was a retrospective quality improvement study. The study included patients admitted from a PACF to one of 2 tertiary care teaching hospitals within the University of Pennsylvania Health System, located in Philadelphia, PA, from August 2020 to December 2021. Patients were included if they had at least one positive culture within 72 hours of admission.

RESULTS

A total of 167 patients and 230 isolates from the study period were evaluated. The majority of positive cultures were from a urinary source (114 of 230, 49.6%). Nineteen patients (11.4%) had a history of multidrug-resistant organisms. The most common empiric antibiotics used were vancomycin (61.7%) and cefepime (59.3%). Sixty-one patients (36.5%) received inappropriate empiric therapy based on the culture results. When comparing our hospitals' general antibiogram to that of only PACF patients, Escherichia coli and Klebsiella pneumoniae had at least a 20% difference in susceptibility to levofloxacin, ceftriaxone, and cefepime. Extended-spectrum β-lactamase resistance was also higher in the PACF cohort (odds ratio, 2.09; 95% confidence interval, 1.4-3.1).

CONCLUSION

Clinically significant differences in antimicrobial susceptibility were found among patients admitted from PACFs compared to our health system's general antibiogram. The increased resistance rates identified in this study support the need for hospitals to evaluate this at-risk patient population, which may drive changes to empiric antibiotic prescribing practices.

The Penn Medicine COVID-19 Therapeutics Committee-Reflections on a Model for Rapid Evidence Review and Dynamic Practice Recommendations During a Public Health Emergency

The Penn Medicine COVID-19 Therapeutics Committee-an interspecialty, clinician-pharmacist, and specialist-front line primary care collaboration-has served as a forum for rapid evidence review and the production of dynamic practice recommendations during the 3-year coronavirus disease 2019 public health emergency. We describe the process by which the committee went about its work and how it navigated specific challenging scenarios. Our target audiences are clinicians, hospital leaders, public health officials, and researchers invested in preparedness for inevitable future threats. Our objectives are to discuss the logistics and challenges of forming an effective committee, undertaking a rapid evidence review process, aligning evidence-based guidelines with operational realities, and iteratively revising recommendations in response to changing pandemic data. We specifically discuss the arc of evidence for corticosteroids; the noble beginnings and dangerous misinformation end of hydroxychloroquine and ivermectin; monoclonal antibodies and emerging viral variants; and patient screening and safety processes for tocilizumab, baricitinib, and nirmatrelvir-ritonavir.

1759. Risk Factors for OPAT-Related Adverse Drug Events: A Case-Control Study

Background

Outpatient parenteral antimicrobial therapy (OPAT) offers numerous clinical advantages, though adverse drug events (ADEs) are a common and potentially preventable challenge that may contribute to 30-day readmissions and other negative outcomes. In January 2021, our OPAT program began documenting all significant ADEs using an electronic template. The purpose of this study was to characterize significant OPAT ADEs and to identify potential risk factors for their development.

Methods

Outpatient parenteral antimicrobial therapy (OPAT) offers numerous clinical advantages, though adverse drug events (ADEs) are a common and potentially preventable challenge that may contribute to 30-day readmissions and other negative outcomes. In January 2021, our OPAT program began documenting all significant ADEs using an electronic template. The purpose of this study was to characterize significant OPAT ADEs and to identify potential risk factors for their development.

Results

Cumulative ADE incidence was 11%, and median time-to-ADE was 13 days after discharge. During the study period, 54 ADE patients vs. 100 control patients were identified. The most common ADEs attributed to OPAT were kidney injury (50%), rash (10%), and leukopenia (9%) (Table 1). Most ADEs resulted in an OPAT regimen change (33%), dosage adjustment (29%), or early cessation of OPAT (21%) (Table 2). In the final logistic regression model, receipt of vancomycin, use of empiric therapy for culture-negative infection, and OPAT duration ≥ 28 days were associated with increased ADE risk, whereas African American race and receipt of ceftriaxone were protective (Table 3).

Conclusion

Several modifiable risk factors may increase the likelihood of an ADE during OPAT and should be carefully considered prior to hospital discharge. Based on these data, OPAT programs should consider employing vancomycin alternatives, diagnostic stewardship, and strategies to minimize duration of therapy.

Disclosures

Kathleen Degnan, MD, Gilead: Grant/Research Support.

1794. Evaluation of Antimicrobial Susceptibility Patterns for Patients Admitted from Post-Acute Care Facilities in the Philadelphia Region

Background

Antimicrobial resistance is a rapidly emerging threat and antibiograms are a key component in guiding empiric antimicrobial selection. Patients admitted from post-acute care facilities (PACF) are at a heightened risk for infections from multi-drug resistant organisms, posing a challenge for clinicians selecting empiric therapy. It is uncommon for antibiograms to differentiate between sources of admission. This study aimed to characterize culture proven infections and the appropriateness of empiric antimicrobial regimens for patients admitted from PACF in the Philadelphia region.

Methods

This was a retrospective quality improvement study that included patients admitted from Philadelphia PACF from August 2020 to June 2021. Patients were included if they had at least one positive culture within 72 hours of admission. Appropriate therapy was determined based on a comparison of empiric antimicrobial selection and susceptibilities that resulted from collected cultures. Descriptive statistics were employed for data analysis.

Results

A total of 106 patients and 154 cultures were evaluated during the study period. The majority of patients received initial empiric coverage for Pseudomonas aeruginosa (79%) and methicillin-resistant Staphylococcus aureus (59%). Over 50% of all cultures had been obtained from urinary sources. Enterococcus spp. were the most commonly isolated gram positive organism (61%) and Escherichia coli was the most common gram negative organism (33%). A portion of patients (32.7%) did not receive appropriate empiric therapy. Discrepancies in susceptibility patterns between our internal antibiogram and PACF patients were most notable for gram negative organisms including decreased levofloxacin susceptibilities to P. mirabilis isolates (89% vs 45%). Other notable discrepancies include decreased meropenem susceptibilities to P. aeruginosa isolates (88% vs 65%). Select susceptibility patterns are reported in Figure 1.

Conclusion

Antimicrobial susceptibility was discordant amongst patients admitted from PACF in the Philadelphia region compared to our general antibiogram. The increased resistance identified supports a need to re-evaluate empiric prescribing guidelines for this specific population.

Disclosures

All Authors: No reported disclosures.

1833. Evaluating the Impact of Reported Beta-Lactam Allergies on Clinical Outcomes in Gram-Negative Bloodstream Infections: A Retrospective Cohort Study

Background

Approximately 15% of hospitalized patients are labeled as beta-lactam (BL) allergic. Despite this, it is estimated that > 90% of patients do not have clinically significant hypersensitivity reactions and are BL-tolerant. The BL allergy label is associated with a host of downstream consequences, including receipt of suboptimal antibiotic therapy, healthcare-associated infections, and bacterial resistance. There are limited data investigating the impact of this allergy label on clinical outcomes in bloodstream infections caused by Gram-negative pathogens (GN-BSI).

Methods

This was a retrospective, single center, cohort study evaluating the impact of BL allergies on clinical outcomes in patients with GN-BSI from January 2017 to August 2021. Adult inpatients with index blood cultures positive for Pseudomonas species or Enterobacterales who received intravenous antibiotics with Gram-negative activity were included. The primary endpoint was time to effective therapy (defined as treatment with in vitro activity against a causative pathogen, as determined by phenotypic susceptibilities) and the key secondary endpoint was 30-day all-cause mortality.

Results

Overall, 120 patients were included, representing 30 BL-allergic (BL-A) and 90 BL-non-allergic (BL-NA) patients. Blood cultures positive for Pseudomonas species or Enterobacterales were evenly distributed (Table 1). Among Enterobacterales, Escherichia coli was implicated in 25% of cases overall. The most common source of infection was intra-abdominal infection. Across groups, median quick Pitt Bacteremia Score was 1 (IQR 0-2). Infectious Diseases was consulted in 37% of BL-A patients vs. 29% of BL-NA patients. Of BL allergies reported, 86% were classified as likely immunoglobulin E (IgE) mediated reactions. Allergy was not consulted in any of these cases. Median time to effective therapy was 162 minutes (IQR 20-824 minutes) vs. 103 minutes (IQR 27-775 minutes) in the BL-A and BL-NA groups, respectively. Thirty-day mortality occurred in 31% of BL-A and 21% of BL-NA patients.

Conclusion

Increased time to effective therapy and mortality rates were observed among patients with reported BL allergies. These findings highlight the importance of allergy clarification in antibiotic stewardship.

Disclosures

Kathleen Degnan, MD, Gilead: Grant/Research Support.

905. Impact of a Real-Time Electronic Alert on Antibiotic Treatment Duration for Pneumonia in Hospitalized Patients

Background

Limiting antibiotic prescribing to the shortest effective duration reduces antibiotic-associated adverse events and resistance. Up to two-thirds of patients receive excessive durations of therapy for pneumonia. This study evaluated the effect of a stewardship intervention to reduce excess antibiotic duration for inpatients with pneumonia.

Methods

A dashboard was developed to generate real-time alerts when inpatients at an academic medical center received antibiotics with an indication of community- or hospital-acquired pneumonia for more than 5 or 7 days, respectively. From November 2019 through April 2021, alerts were regularly reviewed by the antibiotic stewardship (AS) team and intervened upon when patients exceeded the guideline recommended duration of therapy for pneumonia without additional indications for continuing antibiotics. We compared inappropriate duration of therapy pre- and post-implementation of the dashboard by calculating the mean number of excess days of antibiotics beyond the recommended duration. Patients with SARS-CoV-2 infection and patients on hospital services that care for patients with cystic fibrosis, bronchiectasis, or immunocompromising conditions were excluded. Four other hospitals within the same health system that did not utilize the dashboard generated alerts served as a comparison group.

Results

During the intervention period, the AS team reviewed 834 patients with dashboard alerts and documented 115 interventions. For alerts reviewed without intervention, reasons for lack of intervention included active Infectious Diseases consult, additional infection diagnosis requiring a longer duration, and delayed clinical improvement. In the post-implementation period there was a mean of 1.28 excess days of antibiotics for pneumonia compared to the pre-implementation mean of 1.36 excess days. In comparison, aggregating data from the hospitals not utilizing the dashboard, there was a mean of 0.67 excess days post-intervention, compared to a mean 0.62 days pre-intervention.

Conclusion

The pneumonia dashboard is a potentially valuable stewardship tool which may reduce excess days of antibiotics for pneumonia. The dashboard’s impact may be improved by daily review and excluding patients with additional infection diagnoses.

Disclosures

Kathleen Degnan, MD, Gilead: Grant/Research Support.

168. Syndrome-Based Analysis of Oral Antimicrobial Stewardship Opportunities at Hospital Discharge

Background

Suboptimal oral antibiotic prescriptions (OAPs) are prevalent at discharge and contribute to treatment failure, resistance, toxicity, and excess costs. Syndrome-specific prescribing patterns have not been widely described at discharge, nor have specific reasons for excessive treatment durations (the most commonly cited prescribing error).

Methods

Retrospective cohort of patients discharged from a general medicine service at an academic hospital with ≥1 OAP for urinary tract infection (UTI), skin and soft tissue infection (SSTI), or lower respiratory tract infection (LRTI). Study period varied to include a random sample of encounters occurring after the most recent institutional guideline update for each syndrome. Exclusions: multiple infectious indications, discharge against medical advice, parenteral antibiotics at discharge, pregnancy, cystic fibrosis, and immunocompromising conditions. Discharge OAPs were assessed for suboptimal selection, dose, frequency, or duration according to institutional guidelines (with secondary adjudication).

Results

Analysis included 160 encounters: 70 UTIs, 66 SSTIs, and 24 LRTIs. Of 71 (44%) culture-positive infections, Enterobacterales (61%) and Streptococcus spp. (15%) were most often identified. In total, 180 OAPs were issued – most commonly cefpodoxime (21%), cefadroxil (18%), and doxycycline (17%). Overall, 99 (62%) encounters were associated with a suboptimal discharge OAP. Of 138 suboptimal characteristics identified, suboptimal duration was most frequent (57%), specifically excessive duration (45%). Proportion of suboptimal OAPs and their underlying reasons are analyzed by syndrome in Figures 1 and 2, respectively. Miscalculation (39%), intentional selection of guideline-discordant duration (29%), and omission of inpatient antibiotic days (19%) were the most frequent reasons for suboptimal duration (Fig. 3).

Conclusion

Suboptimal discharge OAPs were common for all studied syndromes, most notably SSTI. Excessive duration was a key driver, with reasons for inappropriate duration previously undescribed. Duration miscalculation and selection of appropriate treatment duration are key areas to focus electronic health record enhancements, provider education, and antimicrobial stewardship efforts.

Disclosures

All Authors: No reported disclosures

622. Evaluation of Vascular Access Device Selection in Patients Discharged on Outpatient Parenteral Antimicrobial Therapy

Background

Selection of a vascular access device (VAD) is an important consideration for patients receiving outpatient parenteral antimicrobial therapy (OPAT). Midline catheters (MC) and peripherally inserted central catheters (PICC) are the most commonly placed VADs, with the former recommended by national guidelines to be used for durations no longer than two weeks. These recommendations, however, are based on limited data from heterogeneous populations. As such, we aim to further characterize VAD-associated complications specifically in patients receiving antimicrobials.

Methods

We conducted a retrospective cohort study that included adult patients discharged on OPAT with a newly inserted MC or PICC between January 2020 and August 2020. Patients with non-OPAT VAD indications were excluded. The primary outcome was the incidence of VAD-associated complications, which was further assessed by type and severity. The secondary outcome was time to complication. Multivariable Poisson regression was used to assess the association between VAD type and incidence of VAD-associated complications.

Results

A total of 190 encounters from 181 patients were included for analysis. Baseline demographics are detailed in Table 1. Despite a higher number of complications in the PICC group, rates per 1000 VAD days were not significantly different between VAD types (Table 2). Median time to first complication was 17 days in the overall cohort. Multivariable regression analysis showed those with a dermatologic history had a four-fold increased risk for VAD-associated complications (Table 3). VAD type was not independently associated with the risk of developing a complication.

Conclusion

Our results suggest that the development of VAD-associated complications was strongly associated with patients’ dermatologic history. To our knowledge, dermatologic history has not been previously identified as a risk factor for VAD-associated complications. Thorough assessment of patient-specific risk factors can inform optimal VAD selection for patients discharged on OPAT. Further studies are needed to assess the safety of MC for extended OPAT use.

Disclosures

All Authors: No reported disclosures

82. Assessment of Clinical Outcomes and Antibiotic Prescribing Patterns Following Implementation of the GenMark ePlex® Blood Culture Identification Panel for Gram-positive Bloodstream Infections

Background

Rapid diagnostic testing (RDT) of bloodstream pathogens provides key information sooner than conventional identification and susceptibility testing. The GenMark ePlex® blood culture identification gram-positive (BCID-GP) panel is a molecular-based multiplex platform, with 20 Gram-positive target pathogens and 4 bacterial resistance genes that can be detected within 1.5 hours of blood culture positivity. Published studies have evaluated the accuracy of the ePlex® BCID-GP panel compared to traditional identification methods; however, studies evaluating the impact of this panel on clinical outcomes and prescribing patterns are lacking.

Methods

This multi-center, quasi-experimental study evaluated clinical outcomes and prescribing patterns before (December 2018 – June 2019) and after (August 2019 – January 2020) implementation of the ePlex® BCID-GP panel in June 2019. Hospitalized, adult patients with growth of Enterococcus faecalis, Enterococcus faecium, or Staphylococcus aureus from blood cultures were included. The primary endpoint was time to targeted antibiotic therapy, defined as time from positive Gram-stain to antibiotic adjustment for the infecting pathogen.

Results

A total of 200 patients, 100 in each group, were included. Time to targeted therapy was 47.9 hours in the pre-group versus 24.8 hours in the post-group (p< 0.0001). Time from Gram-stain to organism identification was 23.03 hours (pre) versus 2.56 hours (post), p< 0.0001. There was no statistically significant difference in time from Gram-stain to susceptibility results, hospital length of stay (LOS), or all-cause 30-day mortality.

Conclusion

Implementation of the GenMark ePlex® BCID-GP panel reduced time to targeted antibiotic therapy by nearly 24 hours. Clinical outcomes including hospital LOS and all-cause 30-day mortality did not show a statistical difference, although analysis of a larger sample size is necessary to appropriately assess these outcomes. This study represents the effect of RDT implementation alone, in the absence of stewardship intervention, on antibiotic prescribing patterns. These findings will inform the design of a dedicated RDT antimicrobial stewardship intervention at our institution, while also being generalizable to other institutions with RDT capabilities.

Disclosures

All Authors: No reported disclosures

751. Impact of Changing from a Three-step to Two-step Testing Algorithm for the Diagnosis of Clostridioides difficile

Background

The optimal method for laboratory diagnosis of Clostridioides difficile infection (CDI) remains undefined and national guidelines do not make a recommendation for a preferred diagnostic algorithm. Aiming to improve infection control measures, the Hospital of the University of Pennsylvania changed its testing process for the diagnosis of CDI from a 3-step to a 2-step algorithm (Figure 1) in September 2018. Starting an algorithm with nucleic acid amplification testing (NAAT) has been hypothesized to lead to potential diagnostic uncertainty if the result is positive by NAAT alone, as this test cannot distinguish between active infection and colonization.

Three-Step and Two-Step Diagnostic Testing Algorithms

Methods

This retrospective, single-center, quasi-experimental study included patients ≥ 18 years of age that tested positive for C. difficile between May 1^st, 2018 and January 31^st, 2019. The study period encompassed 4 months prior to the algorithm change, a 1-month washout immediately following the change, and the subsequent 4 months. The primary outcome was proportion of patients who tested positive for C. difficile and received targeted treatment for CDI. Secondary outcomes included total number of patients who tested positive for C. difficile and received targeted treatment for CDI, duration of treatment for CDI, and hospital length of stay.

Results

Sixty-nine patients in the pre-group (3-step) and 75 patients in the post-group (2-step) tested positive for C. difficile. A higher proportion of patients in the post-group tested positive by NAAT alone (59.4% vs. 73.3%). CDI severity and prior history of CDI were similar between groups. The primary outcome occurred in 89.9% of patients in the pre-group and 83.8% in the post-group (p=0.213). Sixty-two patients in each group received targeted treatment for CDI (p=0.213), median treatment duration was 15 (IQR 11.25-25.75) and 14 (IQR 11-25) days (p=0.505), and median hospital length of stay was 9 (IQR 3-15) and 6 (IQR 3-20) days (p=0.690) in the pre-group and post-group, respectively.

Conclusion

Although there was a higher percentage of patients in the post-group that tested positive for C. difficile by NAAT alone, there was no difference in the proportion or total number of patients who received targeted CDI treatment between time periods.

Disclosures

All Authors: No reported disclosures

54. Effectiveness of a Venous Catheter Stewardship Intervention Targeting Parenteral Antimicrobial Therapy at Hospital Discharge

Background

Peripherally inserted central catheters (PICCs) and midlines are often used in hospitalized patients who require outpatient parenteral antimicrobial therapy (OPAT) upon discharge. PICCs/midlines offer ease of insertion but still carry the risks of venous thrombosis, phlebitis, and catheter-associated infection. We report the results of a prospective audit and feedback (PAF) intervention targeting the placement of PICCs/midlines for OPAT at our institution.

Methods

We prospectively identified a cohort of patients identified by a real-time PICC/midline alert from 5/20/2019 through 5/29/2020 at two large academic medical centers. Alerts were generated by a third-party interface with the electronic health record and identified new line orders with an antimicrobial indication selected. Patients without infectious diseases (ID) consult underwent PAF by the antimicrobial stewardship team. Descriptive statistics were used to characterize patients, interventions, and outcomes.

Results

During the study period, 1267 PICC/midline alerts were identified. Most were excluded due to ID consult (85.4%). After exclusions, 113 alerts underwent full review. Median patient age was 64 years with female predominance (54.2%). Reviewable alerts most commonly originated from Pulmonary (36.5%) and Hospitalist (26.0%) services. The most frequent antimicrobial indications were pneumonia (37.5%) and bloodstream infection (28.1%), and the most frequently ordered antimicrobials were cefepime (27.1%) and piperacillin-tazobactam (17.7%). Median time from line order to insertion was 22 hours and from line insertion to discharge was 48 hours. Of 113 alerts reviewed by the stewardship team, 26 (23.0%) resulted in a recommendation to avoid line placement and 45 (39.8%) resulted in at least one specific stewardship recommendation (Table 1). Recommendations were fully or partially accepted in 58.3% of instances.

TABLE 1. Interventions Resulting from Prospective Venous Catheter Stewardship

Conclusion

Prospective audit of PICC/midline orders for OPAT identified a line-sparing opportunity in nearly 1 in 4 cases. Where line avoidance was not possible, other opportunities for antimicrobial optimization were common. This high-yield intervention should be considered for institutions that do not mandate infectious diseases consult for all OPAT discharges.

Disclosures

All Authors: No reported disclosures

275. Comparison of Cefazolin versus Nafcillin for Methicillin-Susceptible Staphylococcus aureus Bacteremia with a Deep-Seated Source

Background

Historically, anti-staphylococcal penicillins have been the treatment of choice for methicillin-susceptible Staphylococcus aureus (MSSA) infections. However, cefazolin may have advantages over these agents including convenience and tolerability. Despite several studies finding similar rates of clinical efficacy using cefazolin with fewer adverse drug events, some prescribers remain hesitant to use this agent due to concern for an inoculum effect in deep-seated infections. The purpose of this study was to compare cefazolin and nafcillin for the treatment of MSSA bacteremia with exclusively deep-seated sources.

Methods

Adult patients who were admitted with MSSA bloodstream infections (BSI) treated with cefazolin or nafcillin between March 2017 and October 2019 were identified. Patients were included if their BSI had a deep-seated source, defined as endocarditis, osteomyelitis, septic arthritis, pneumonia, prosthetic material, mediastinitis, or abscess. Patients were excluded if they had polymicrobial BSI, central nervous system infection, or received less than 7 days of therapy. The primary efficacy outcome (PEO) was a composite of treatment failure, 60-day mortality, and 60-day infection relapse, and was assessed using multivariate logistic regression. The primary safety outcome (PSO) was discontinuation of therapy due to adverse drug events, which was assessed with a chi-square test.

Results

A total of 164 patients were included in this analysis (141 treated with cefazolin and 23 with nafcillin). There were no significant differences in the baseline characteristics collected (Table 1), and the most common deep-seated sources were prosthetic material and endocarditis. Treatment with nafcillin was not found to be protective against the PEO in multivariate analysis (aOR, 1.19; 95% CI, 0.42 to 3.39; P = 0.75), and the PSO was reached significantly more often among nafcillin recipients compared to those treated with cefazolin (7/23 [30.4%] versus 8/141 [5.7%], P < 0.0001).

Conclusion

Though the sample size was smaller than desired, cefazolin and nafcillin appeared to have similar efficacy for the treatment of MSSA BSIs with deep-seated sources. Nafcillin was associated with significantly more adverse drug events leading to discontinuation of therapy.

Disclosures

All Authors: No reported disclosures

Assessing an intervention to improve the safety of automatic stop orders for inpatient antimicrobials

Background

Automatic stop orders (ASOs) for antimicrobials have been recommended as a component of antimicrobial stewardship programs, but may result in unintentional treatment interruption due to failure of providers to re-order an antimicrobial medication. We examined the impact of a multifaceted intervention designed to reduce the potential harms of interrupting antimicrobial treatment due to ASOs.

Methods

An intervention was implemented that included pharmacist review of expiring antimicrobials as well as provider education to encourage use of a long-term antimicrobial order set for commonly used prophylactic antimicrobials. Pharmacist interventions and antimicrobial re-ordering was recorded. Percent of missed doses of a commonly used prophylactic antimicrobial, single strength co-trimoxazole, was compared pre- and post-intervention using a chi-squared test.

Results

From November 1, 2015 to November 30, 2016, there were 401 individual pharmacist interventions for antimicrobial ASOs, resulting in 295 instances of antimicrobial re-ordering. The total percent of presumed missed single strength co-trimoxazole doses was reduced from 8.4% to 6.2% post-intervention (P<0.001).

Conclusions

This study found that a targeted intervention was associated with a reduction in unintended antimicrobial treatment interruption related to ASOs.

1572. Evaluation of Vancomycin Levels Following Weight-Based Pre-operative and Re-warming Vancomycin Dosing in Cardiac Surgery

Background

Weight-based dosing of vancomycin in the pre-operative setting is standard practice at our institution based on the 2013 Clinical Practice Guidelines for Antimicrobial Prophylaxis in Surgery. Our antimicrobial subcommittee recommended a weight-based dosing (15 mg/kg/dose) approach to negate the need for a subsequent vancomycin dose during rewarming in cases requiring cardiopulmonary bypass (CPB). However, after discussion with all perioperative stakeholders, administration of vancomycin 1 g intravenously for all patients on CPB at rewarming continued. The aim of this study was to determine whether subsequent rewarming vancomycin doses contributed to the development of postoperative acute kidney injury (AKI).

Methods

This was a prospective cohort study of all cardiac surgery patients undergoing surgery from April 16, 2018 through April 27, 2018 for the development of AKI as defined by RIFLE criteria. Institutional guidelines recommend vancomycin as perioperative prophylaxis in all cardiac surgery cases with a preoperative 15 mg/kg dose, a 1 g rewarming dose, and nomogram-based post-operative dosing. Vancomycin troughs were obtained prior to the first post-operative dose in the intensive care unit. Serum creatinine was recorded on the post-op day (POD) 0, POD 1, and POD 7.

Results

Data were collected on 54 patients over a 2-week period. The median age was 64 years of age, with 41 (76%) male patients. Seven patients (13%) had a prior diagnosis of chronic kidney disease (CKD). Post-op AKI developed in 8 patients (15%) by POD 7; two of which had CKD at baseline. All patients received appropriate preoperative and postoperative dosing. Forty-nine (91%) patients had trough levels obtained, with the median trough 7.6 μg/mL (range 2 – 15.9 μg/mL) prior to the first nomogram-based post-operative vancomycin dose. Higher rates of AKI were associated with a longer duration of CPB rather than vancomycin levels obtained.

Conclusion

The current practice of redosing 1 g vancomycin at rewarming did not appear to contribute higher rates of AKI. In addition, all vancomycin trough levels reviewed were less than 20 μg/mL. Levels observed in this study are lower than previously described in the literature to cause nephrotoxicity. Further evaluation of vancomycin use in this setting is warranted

Disclosures

All authors: No reported disclosures.

1012. Characterization of Antibiotic Superutilizers in the Inpatient Setting

Background

Inappropriate use of antibiotics is a major public health concern that contributes to increased antibiotic resistance, adverse effects, and healthcare costs. Little is known about the highest utilizers, or superutilizers, who may be appropriate targets for antibiotic stewardship efforts. The purpose of this study was to characterize superutilizers at an academic hospital.

Methods

All adult patients who were admitted to the Hospital of the University of Pennsylvania and received at least one day of antibiotics between July 1, 2017 and June 30, 2018 were identified. All inpatient administrations for systemic antibacterial agents were identified. Antibiotics given in procedural areas and the emergency department were excluded, as were any antifungals and antivirals. Usage was reported as days of therapy (DOT). We compared the demographics and DOT among the superutilizers (defined as the top 1% of patients) to different groupings of the rest of the population.

Results

Overall, 13,559 patients (and 183,082 DOT) were included in the analysis, including 136 superutilizers. The superutilizers received 15% of the total antibacterial DOT and a median of 56 DOT during the 12-month period. (table)

Conclusion

Inpatient antibiotic use is unevenly distributed across the population. Higher meropenem and sulfamethoxazole/trimethoprim DOT suggest that treatment of multidrug-resistant organisms and opportunistic infection prophylaxis are more common in the superutilizer group. Additional study is needed to determine whether antimicrobial stewardship efforts could impact antibiotic use in the superutilizer population.

Disclosures

All authors: No reported disclosures.

124. Impact of Levofloxacin MIC on Outcomes with Levofloxacin Step-down Therapy in Enterobacteriaceae Bloodstream Infections

Background

The Clinical and Laboratory Standards Institute reduced the levofloxacin minimum inhibitory concentration (MIC) breakpoint from ≤2 to ≤0.5 mg/L for Enterobacteriaceae in 2019 guidelines. The reduction is based on Monte Carlo simulations for a levofloxacin dose of 750 mg daily. The aim of this study was to determine whether there was a difference in clinical outcomes in the treatment of Enterobacteriaceae bacteremia with levofloxacin step-down therapy retrospectively comparing patients with isolates with low levofloxacin MICs (≤0.5 mg/L) to high MICs (1–2 mg/L).

Methods

This retrospective, two-center cohort study included patients ≥18 years of age with a monomicrobial Enterobacteriaceae bacteremia with a levofloxacin MIC ≤2 mg/L from March 2017 through December 2018. Patients had to have received treatment with ≥3 days of levofloxacin step-down therapy, initial intravenous therapy with an agent active against the isolated organism, and total duration not exceeding 16 days from first negative blood culture. A subset of patients whose isolates had low levofloxacin MICs were randomly selected for comparison to all patients with high levofloxacin MICs in a 3:1 ratio. The primary outcome was a composite endpoint of recurrence and mortality within 30 days of completion of the antibiotic course. Secondary outcomes included post-culture length of stay (LOS) and 30-day readmission rate.

Results

Thirty-three patients with high MIC and 99 with low MIC were included. Urinary source was predominant and occurred in 44% of patients, and Escherichia coli was the infecting organism in 48%. Over 80% of patients experienced source resolution or control. The composite endpoint occurred in 8.1% of the low MIC group and 9.1% of the high MIC group (P = 0.856). Median LOS was 4.9 days (IQR 3.7–8.0) in the low MIC group and 4.3 days (IQR 3.2–6.8) in the high MIC group (P = 0.384), and readmission rate was 17.2% in the low MIC group and 15.2% in the high MIC group (P = 0.787).

Conclusion

There was no between-group difference in the primary outcome of recurrence and mortality, with a low overall event rate and short LOS post-culture. These results suggest that levofloxacin effectiveness may be sustained in patients with MICs of 1 or 2 despite levofloxacin not meeting susceptibility criteria by new definitions.

Disclosures

All authors: No reported disclosures.

2445. Risk for Readmission and Mortality Amongst LTACH Residents with New-Onset Healthcare-Associated Infections

Background

Long-term acute care hospitals (LTACH) provide cost-effective alternatives for stable patients requiring ICU-level care. LTACH patients are at increased risk for adverse outcomes including healthcare-associated infections (HAI). There is a paucity of data describing outcomes associated with HAIs in LTACH patients.

Methods

This was a single-center, retrospective study of LTACH patients over a 3 year period. Patients with an HAI (bloodstream [BSI], pneumonia [PNA], urinary tract [UTI], and Clostridioides difficile [CDI] infections) as defined by NHSN criteria were matched by length of stay (LOS) at the time of inclusion to unexposed patients. Follow-up was 30 days from the date of inclusion. The primary outcome was a composite of unplanned readmission to an acute care hospital or death at the LTACH. Secondary outcomes included all-cause mortality. Patients with HAIs were further evaluated to determine risk factors associated with readmission Antibiotics and cultured organisms were collected. Outcomes were analyzed using Cox proportional hazards model. Variables found to have a P < 0.1 on univariate analysis and those of clinical interest were included in the models.

Results

250 patients were included, 125 in each group. The distribution of HAIs was 40 BSI, 39 UTI, 26 PNA, and 20 CDI. The incidence of the primary outcome and mortality were 26.0% and 11.6% respectively. HAI was associated with increased risk of the primary outcome, but the effect varied over time: Risk increased seven-fold during the first 5 days (HR, 7.47 [95% CI, 2.86–19.42]) but was smaller and non-significant after day five (HR, 1.94 [95% CI, 0.85–4.43]). Mortality was not significantly different between groups (HR, 1.58 [95% CI, 0.74–3.38]). After adjustment, only hypotension (HR, 2.27 [95% CI 1.21–4.27]) and referral hospital LOS > 28 days (HR, 1.97 [95% CI 1.10–3.53]) were associated with readmission. 37% of cultured organisms were multi-drug-resistant. 17% of Enterobacteriaceae were carbapenem resistant. Empiric antibiotics failed to cover in 35% of infections.

Conclusion

HAI was associated with a significant increase in risk of readmission. Exploration of modifiable variables of infection, including hypotension and antibiotic selection, may help to reduce rates of readmission.

Disclosures

All authors: No reported disclosures.

1814. External Validation of Precision Antibiotic Therapy for Enterococcal Bloodstream Infections

Background

ILÚM Heath Solutions, an infectious diseases software platform, developed precision antibiotic therapy (PAT) software to guide selection of therapy using data science, patient-specific factors, as well as historical patient, pharmacy, and microbiologic data. PAT reports percentages reflecting likelihood of susceptibility across a panel of antibiotics, identifying patients at high risk for resistant organisms. PAT has previously demonstrated high accuracy for predicting susceptibility of Enterobacteriaceae in bloodstream infections (BSIs) and risk for multi-drug resistance. The objective of this study was to validate PAT predictive capabilities in enterococcal BSIs and to assess accuracy in risk-stratifying patients for vancomycin-resistant Enterococcus spp. (VRE).

Methods

This retrospective cohort study included patients with an index enterococcal BSI from January 2016 through December 2016. The primary outcome was the performance characteristics of PAT in accurately predicting the risk of VRE, elaborated with sensitivity and specificity rates across varying PAT thresholds. Receiver operating characteristics (ROC) curve analyses were performed to identify an acceptable PAT threshold to define high risk for VRE. Brier score calculations were used to compare accuracy of PAT predictions to that of the institutional antibiogram.

Results

ROC curve analysis (Figure 1) demonstrated an area under the curve of 0.94, indicating excellent discrimination. The Brier scores for the institutional antibiogram and PAT software were 0.067 and 0.075, respectively, representing a similar degree in accuracy. Species-level Brier scores for the institutional antibiogram and PAT were 0.043 and 0.065, respectively, for E. faecalis and 0.093 and 0.073, respectively, for E. faecium.

Conclusion

PAT software was able to discriminate enterococcal BSIs resistant and susceptible to vancomycin. Similar to previous results seen with Enterobacteriaceae, PAT may be useful to accurately predict susceptibilities for Enterococcus spp., particularly for E. faecium.

Disclosures

S. Overly, ILÚM Health Solutions: Consultant, Salary. J. Mehta, ILUM Health Solutions: Consultant, Salary.

Comparison of Unit-Specific and Hospital-Wide Antibiograms Potential Implications for Selection of Empirical Antimicrobial Therapy

Objective.

To identify differences between unit-specific and hospital-wide antibiograms and to determine the potential impact of these differences on selection of empirical antimicrobial therapy.

Setting.

A 625-bed tertiary care medical center.

Methods.

Antimicrobial susceptibility results were collected for all inpatient clinical bacterial isolates recovered over a 3-year period; isolates were categorized by the hospital location of the patient at the time of sampling and by the anatomic site from which the isolate was recovered. Antibiograms from each unit were compiled for the most commonly isolated organisms and were compared to the hospital-wide antibiogram.

Results.

A total of 9,970 bacterial isolates were evaluated in this study, including 2,646 enterococcal isolates, 2,806 S. aureus isolates, 2,795 E. coli isolates, and 1,723 Pseudomonas aeruginosa isolates. The percentages of bacterial isolates resistant to antimicrobials were significantly higher in the medical ICU and surgical ICU than the hospital-wide antibiogram would have predicted, whereas the percentages of isolates susceptible to antimicrobials were significantly higher in the non-ICU units, compared with the hospital overall. However, on general medicine units, the prevalence of susceptibility to levofloxacin was significantly lower than that for the hospital overall.

Conclusions.

Unit-specific antibiograms are important for making informed decisions about empirical antimicrobial therapy, because the hospital-wide antibiogram may mask important differences in susceptibility rates across different units. These differences may have important implications for selecting the optimal empirical antimicrobial therapy.

Comparison of prior authorization and prospective audit with feedback for antimicrobial stewardship

OBJECTIVE

Although prior authorization and prospective audit with feedback are both effective antimicrobial stewardship program (ASP) strategies, the relative impact of these approaches remains unclear. We compared these core ASP strategies at an academic medical center.

DESIGN

Quasi-experimental study.

METHODS

We compared antimicrobial use during the 24 months before and after implementation of an ASP strategy change. The ASP used prior authorization alone during the preintervention period, June 2007 through May 2009. In June 2009, many antimicrobials were unrestricted and prospective audit was implemented for cefepime, piperacillin/tazobactam, and vancomycin, marking the start of the postintervention period, July 2009 through June 2011. All adult inpatients who received more than or equal to 1 dose of an antimicrobial were included. The primary end point was antimicrobial consumption in days of therapy per 1,000 patient-days (DOT/1,000-PD). Secondary end points included length of stay (LOS).

RESULTS

In total, 55,336 patients were included (29,660 preintervention and 25,676 postintervention). During the preintervention period, both total systemic antimicrobial use (-9.75 DOT/1,000-PD per month) and broad-spectrum anti-gram-negative antimicrobial use (-4.00 DOT/1,000-PD) declined. After the introduction of prospective audit with feedback, however, both total antimicrobial use (+9.65 DOT/1,000-PD per month; P < .001) and broad-spectrum anti-gram-negative antimicrobial use (+4.80 DOT/1,000-PD per month; P < .001) increased significantly. Use of cefepime and piperacillin/tazobactam both significantly increased after the intervention (P = .03). Hospital LOS and LOS after first antimicrobial dose also significantly increased after the intervention (P = .016 and .004, respectively).

CONCLUSIONS

Significant increases in antimicrobial consumption and LOS were observed after the change in ASP strategy.

Impact of antimicrobial stewardship programme changes on unnecessary double anaerobic coverage therapy

BACKGROUND

Concern has been raised over the practice of unnecessary double anaerobic coverage therapy (DACT) in the hospital setting. However, the incidence of and risk factors for unnecessary DACT are not well studied. On 8 September 2008, the antimicrobial stewardship programme (ASP) at our institution was modified such that several antibiotics, including ampicillin/sulbactam and metronidazole, no longer required pre-approval. We anticipated that this change would increase both unnecessary DACT and target antibiotic consumption.

METHODS

A nested case-control study was conducted to determine the cumulative incidence of and risk factors for unnecessary DACT. Cases were subjects who received unnecessary DACT while controls were subjects who did not receive DACT or who received necessary DACT. Segmented regression analysis was subsequently performed to evaluate the impact of ASP changes on unnecessary DACT and consumption of target antibiotics.

RESULTS

From October 2007 to September 2009, the cumulative incidence of unnecessary DACT was 2.3% [95% confidence interval (CI) 1.7-3.1]. Independent risk factors for unnecessary DACT [adjusted odds ratio (95% CI); P value] included hospitalization on a surgical ward [3.51 (1.03-12.02); P = 0.002], hospitalization on an obstetrics and gynaecology ward [9.07 (2.54-32.40); P = 0.002] and underlying metastatic malignancy [3.18 (1.38-7.09); P = 0.006]. The ASP change was associated with an increase in ampicillin/sulbactam and metronidazole consumption. However, there was no significant impact on unnecessary DACT prescribing.

CONCLUSIONS

Although uncommon, unnecessary DACT is more prevalent in specific services. Future qualitative studies focusing on these specific subgroups would be useful in elucidating this problem more clearly. The ASP changes were not associated with increases in unnecessary DACT.

Effect of an antibiotic algorithm on the adequacy of empiric antibiotic therapy given by a medical emergency team

INTRODUCTION

Delayed administration of effective antimicrobial therapy increases mortality in patients with septic shock. Empiric antibiotic selection in this setting can be inaccurate. The objective of this study was to determine whether an antibiotic algorithm (AA) tailored to institutional resistance patterns improves the adequacy of antimicrobial therapy.

METHODS

A retrospective review of our rapid response system database was performed. Patients with possible sepsis with positive microbiological culture results were enrolled. Pathogens identified by culture were used to determine adequacy of antibiotic selection before and after implementation of an AA.

RESULTS

A total of 234 patients with septic shock were reviewed (before AA, n = 36; after AA, n = 198). Seventy-two patients had positive cultures and were enrolled (before AA, n = 13; after AA, n = 59). Significantly more patients received adequate coverage after AA implementation (54% vs 86%, P = .02). Before AA, inadequate Gram-negative coverage was the most common reason for failure. Reasons for failure in the after-AA group were nonadherence to the algorithm (n = 5) and multidrug-resistant pathogens (n = 3). The algorithm failed in patients with vancomycin-resistant enterococci (n = 3), multidrug-resistant Klebsiella pneumoniae (n = 1), and Candida albicans (n = 1).

CONCLUSIONS

The use of an AA significantly improves the adequacy of empiric antimicrobial therapy.

Impact of automatic orders to discontinue vancomycin therapy on vancomycin use in an antimicrobial stewardship program

We examined the possible unintended consequences of a 72-hour automatic order to discontinue vancomycin therapy in an antimicrobial stewardship program (ASP). Of 120 patients, 11 had vancomycin therapy discontinued at 72 hours without a call to the ASP, and 7 experienced a treatment interruption of 6-36 hours. All discontinuation of therapy was considered appropriate, and the 7 treatment interruptions did not have clear clinical consequences. Only one-third of patients had ASP stickers that warned of impending discontinuation of vancomycin therapy placed appropriately in the medical record.

Three- and four-dimensional-quantitative structure activity relationship (3D/4D-QSAR) analyses of CYP2C9 inhibitors

The interaction of competitive type inhibitors with the active site of cytochrome P450 (CYP) 2C9 has been predicted using three- and four-dimensional quantitative structure activity relationship (3D-/4D-QSAR) models constructed using previously unreported and literature-derived data. 3D-QSAR pharmacophore models of the common structural features of CYP2C9 inhibitors were built using the program Catalyst and compared with 3D- and 4D-QSAR partial least-squares models, which use molecular surface-weighted holistic invariant molecular descriptors of the size and shape of inhibitors. The Catalyst models generated from multiple conformers of competitive inhibitors of CYP2C9 activities contained at least one hydrophobic and two hydrogen bond acceptor/donor regions. Catalyst model 1 was constructed with Ki(apparent) values for inhibitors of tolbutamide and diclofenac 4'-hydroxylation (n = 9). Catalyst model 2 was generated from literature Ki(apparent) values for (S)-warfarin 7-hydroxylation (n = 29), and Catalyst model 3 from literature IC50 values for tolbutamide 4-hydroxylation (n = 13). These three models illustrated correlation values of observed and predicted inhibition for CYP2C9 of r = 0.91, 0.89, and 0.71, respectively. Catalyst pharmacophores generated with Ki(apparent) values were validated by predicting the Ki(apparent) value of a test set of CYP2C9 inhibitors also derived from the literature (n = 14). Twelve of fourteen of these Ki(apparent) values were predicted to be within 1 log residual of the observed value using Catalyst model 1, whereas Catalyst model 2 predicted 10 of 14 Ki(apparent) values. The corresponding partial least-squares molecular surface-weighted holistic invariant molecular 3D- and 4D-QSAR models for all CYP2C9 data sets yielded predictable models as assessed using cross-validation. These 3D- and 4D-QSAR models of CYP inhibition will aid in future prediction of drug-drug interactions.

The romantic sexology of John Addington Symonds

This paper examines a radical text by the English Classicist and homosexual, John Addington Symonds (1840-1893). Through a close study of an unpublished and long concealed manuscript, "A Problem in Modern Ethics" (1891), Symonds's political vision and the odd form of writing it takes is revealed as romantic in character. Symonds polemicizes against the pathologization of homosexuals in the legal-medical discourses of the time and advocates on behalf of a latent homosexual ethics, shunned from modern Western society, but continuing to hold forth a promise for the civic and moral renewal of Western countries. Against the positions of Krafft-Ebing and others, Symonds argues for the acceptance of "manly love," in the spirit of the ancients, as a source of moral inspiration for a declining Europe. Where Symonds is often read by historians of homosexual radicalism as a precursor to the radical tradition of the 20th century, romantic acceptance of the untimeliness of his moral vision, indicates less a politically progressive than a romantically fatalistic enterprise.

Three and four dimensional-quantitative structure activity relationship (3D/4D-QSAR) analyses of CYP2D6 inhibitors

Three- and four-dimensional quantitative structure activity relationship (3D/4D-QSAR) pharmacophore models of competitive inhibitors of CYP2D6 were constructed using data from our laboratory or the literature. The 3D-QSAR pharmacophore models of the common structural features of CYP2D6 inhibitors were built using the program Catalyst (Molecular Simulations, San Diego, CA, USA). These 3D-QSAR models were compared with 3D and 4D-QSAR partial least squares (PLS) models which were constructed using molecular surface-weighted holistic invariant molecular (MS-WHIM) descriptors of size and shape of inhibitors. The first Catalyst model was generated from multiple conformers of competitive inhibitors (n = 20) of CYP2D6 mediated bufurolol 1'-hydroxylation. This model demonstrated a correlation of observed and predicted Ki (apparent) values of r = 0.75. A second Catalyst model was constructed from literature derived Ki (apparent) values (n = 31) for the inhibition of CYP2D6. This model provided a correlation of observed and predicted inhibition for CYP2D6 of r = 0.91. Both Catalyst Ki pharmacophores were then validated by predicting the Ki (apparent) of a test set of known CYP2D6 inhibitors (n = 15). Ten out of 15 of these Ki (apparent) values were predicted to be within one log residual of the observed value using our CYP2D6 inhibitor model, while the literature model predicted nine out of 15 values. Similarly, 3D- and 4D-QSARs derived from PLS MS-WHIM for our dataset yielded predictable models as assessed using cross-validation. The corresponding cross-validated PLS MS-WHIM model for the literature dataset yielded a comparable 3D-QSAR and improved 4D-QSAR value. Such computational models will aid in future prediction of drug-drug interactions.

Three- and four-dimensional quantitative structure activity relationship analyses of cytochrome P-450 3A4 inhibitors

The program Catalyst was used to build three-dimensional quantitative structure activity relationship (3D-QSAR) pharmacophore models of the structural features common to competitive-type inhibitors of cytochrome P-450 (CYP) 3A4. These were compared with 3D- and four-dimensional (4D)-QSAR partial least-squares (PLS) models built using molecular surface-weighted holistic invariant molecular (MS-WHIM) descriptors for size and shape of the inhibitor. The Catalyst pharmacophore model generated from multiple conformers of competitive inhibitors of CYP3A4-mediated midazolam 1'-hydroxylation (n = 14) yielded a high correlation of observed and predicted Ki values of r = 0.91. Similarly, PLS MS-WHIM was used to produce 3D- and 4D-QSARs for this data set and produced models that were statistically predictable after cross-validation. Two additional Catalyst pharmacophores were constructed from literature Ki values (n = 32) derived from the inhibition of CYP3A-mediated cyclosporin A metabolism and IC50 data (n = 22) from the inhibition of CYP3A4-mediated quinine 3-hydroxylation. These Catalyst pharmacophores illustrated correlations of observed and predicted inhibition for CYP3A4 of r = 0.77 and 0.92, respectively. The corresponding 4D-QSARs generated by PLS MS-WHIM for these data sets were of comparable quality as judged by cross-validation. Both Ki pharmacophores generated with Catalyst were also validated by predicting the Ki(apparent) values of a test set of eight CYP3A4 inhibitors not included in either model. In seven of eight cases, the residuals of the predicted Ki(apparent) values were within 1 log unit of the observed values. The 3D- and 4D-QSAR models produced in this study suggest the utility of future in silico prediction of CYP3A4-mediated drug-drug interactions.

Field observations of yawning and activity in humans

Rates of wrist activity and yawning were recorded continuously for 7-15 days in adult human male and female subjects. In the 15 min following 747 yawns wrist motion increased reliably in all subject records. The data were consistent with an hypothesis that yawning is predictive of an increase in activity level. In a second study, data from daily logs kept by 45 subjects confirmed previous findings that yawning frequency is unrelated to prior amount of sleep, or to times of awaking or retiring. More yawning occurred during the week than during weekends.

Wrist motion rhythm phase shifts in travelers may differ from changes in time zones

Wrist motions (223-471)/5 min were measured during 17-32 days of continuous recordings made from human passengers as they traveled across zero to five time zones for business and pleasure. The travelers all exhibited daily cycles of activity and rest. The duration of daily activity, alpha, was 1.1 h less at the destination; the mean was 63 wrist motions/5 min less at the destination. Phase shifts of the daily rhythm (e.g., acrophases, 0.0 to 5.3 h) advanced or delayed in the direction expected from time zone changes. However, the magnitude of the phase shifts differed (e.g., as much as 2.3 h) from the expected changes because of transmeridian travel and there were phase shifts even when there was no change in time zone. Differences were observed in phase shifts assessed by different methodologies of determining phase (waveforms, onsets, offsets, acrophases).

Structures and molecules involved in generation and regulation of biological rhythms in vertebrates and invertebrates

Melatonin from the retina and the pineal gland functions in neuroendocrine hierarchies. Photoreceptors--eyes and extraretinal--detect light. Oscillators--pineal and suprachiasmatic nuclei--act as pacemakers. Driven neuroendocrine rhythms carry temporal hormone signals throughout the body. Light controls melatonin: light sets the phase of the melatonin rhythm and determines the duration of melatonin synthesis. By these means, circadian rhythms (e.g., in locomotor activity and body temperature) and seasonal rhythms (e.g., in reproduction) are controlled.

Individual, phase, and weekly variations in daily cycles of wrist activity in freeliving humans

Wrist activity was monitored in 17 college students for 11-15 days each. Records of individuals had distinctive patterns, like fingerprints. The subjects all exhibited daily cycles in their activity with activity during the daytime and with period lengths close to 24 h. There was individual variation in average phase (onset 5.3 h, offset 4.5 h, acrophase 6.1 h). Individual subjects all showed 7-day oscillations in their activity patterns associated with the weekly work-leisure schedules. During the leisure weekends, the subjects as a group had a 2.1-h delay in onset, a 1.5-h delay in acrophase, and a 0.8-h shortening in alpha.

Wrist activity in a woman: daily, weekly, menstrual, lunar, annual cycles?

Wrist activity was monitored continuously for one year in a woman who went about her normal life. The year of data were analyzed for changes and rhythms--daily, weekly, menstrual, lunar, annual. For each day, average motions/5 minutes, activity onset, activity offset, alpha (duration of activity), and acrophase were measured. Periodograms and average daily wave forms were calculated. Well-defined, entrained, daily rest-activity cycles were observed throughout the year with periods close to 24 hours. There was weekend delay (0.7 hours) in onset, weekend decrease in alpha (1.0 hours), and weekend advance of acrophase (0.4 hours). Motions/5 minutes decreased 9%, onsets were 0.3 hours later, and alphas were 0.4 hours shorter on menstrual cycle days 8 through 18 which should have encompassed the time of ovulation. Lunar phase had no effect. Annual changes in onset (1.1 hours), offset (1.2 hours), and acrophase (1.1 hours) were attributed to the 1-hour change between standard and daylight savings time.

Human daily rhythms measured for one year

Four human subjects recorded their wake-up and to-sleep times for one year each. The data were plotted to display individual circadian rhythms and the data were analyzed statistically. First, individuals had characteristic patterns in which visible changes in the patterns were observed mainly when time zones were changed because of travel. Second, the months with the latest wake-up and latest to-sleep times concentrated around the winter solstice; the months with the earliest wake-up and earliest to-sleep times concentrated around the fall equinox. Third, new moon versus full moon days were not different. Fourth, one-hour changes between standard and daylight savings time in the USA were reflected by near one-hour changes in two subjects, but not in a third. Fifth, weekend delays in wake-up time (0.8-1.6 hours), weekend delays in to-sleep time (0.1-0.5 hours), and shorter weekend awake time (0.8-1.3 hours) were observed. Sixth, throughout the year, wake-up times were close to the time of sunrise, but to-sleep times were several hours past sunset.

Day-night differences in the vesicle populations of nerve terminals in the rat and chick pineal gland

Day-night differences in the ultrastructure of pineal neuronal elements were quantitated in the rat and the chick--two species that exhibit important differences in adrenergic control of melatonin synthesis. Area densities of small clear vesicles (40-60 nm) and small dense-cored vesicles (40-60 nm) in nerve terminals were significantly reduced during the night in the rat. In the chick, there were no day-night differences in the frequency of clear vesicles, but the number of small dense-cored vesicles tended to be greater at night. There was no effect of day-night sampling on area densities of large dense-cored vesicles (80-120 nm) in either species. These findings are consistent with biochemical evidence for day-night species differences in the adrenergic control of pineal function.

Weekly phase shifts of rhythms self-reported by almost feral human students in the USA and Spain

Eleven students in the USA and fifteen students in Spain wrote their wake-up and to-sleep times on forms for a month. The subjects reported large day-to-day phase shifts of magnitude comparable to those of travelers and shiftworkers. All individuals exhibited some large phase shifts of their day-to-day wake-up and to-sleep times (largest shift average, 4.54 hours; range, -12.7 to +13.9 hours). The students had daily cycles and weekly cycles in their wake-up and to-sleep times. Synchrony (entrainment) with the 24-hour environment was achieved by large weekly phase advances (individual averages ranged 1.2-4.8 hours) rather than by small daily adjustments. There was considerable variation in awake time: there were 2-3 hour differences between individuals, and there were 3.2 hour differences depending on day of the week. Alarm use appeared to be the Zeitgeber, in contrast to laboratory studies which show light and social Zeitgebers for humans. There was a 4 hour difference between the Spanish and USA students which was attributed to the 5 hour difference in time zones. Wake-up time and prior to-sleep time were interdependent.

Advancing schedules and constant light produce faster resynchronization of circadian rhythms

House sparrows, Passer domesticus, were subjected to rotated light-dark (LD) cycles that consisted of repeated 8-hr advances or delays of 5 days of LD 8:16, with intervening 40-80 hr of constant dark or light. Sparrows reset the fastest (by the second cycle) when they were advanced with intervening constant light (LL). They reset the slowest (taking six cycles) when they were delayed with intervening constant dark (DD).

Photoperiod modifies daily maps of light and dark sensitivity for N-acetyltransferase activity in pineal glands of 3-week old Gallus domesticus

N-acetyltransferase (NAT) activity in pineal glands exhibits a circadian rhythm with peak activity occurring in the dark-time. We previously showed that in Gallus domesticus chicks pretreated with LD12:12, NAT activity was increased by dark exposure (peak dark sensitivity occurred during the expected dark-time) or decreased by light at night (peak light sensitivity occurred early in the night during the time of dark sensitivity). In this study we mapped dark sensitivity vs time (for NAT activity increase in response to 2 h dark pulses), and light sensitivity vs time (for NAT activity decrease in response to 10 min or 30 min light pulses) over a cycle for 3-week old chicks, Gallus domesticus, pretreated with long (LD16:8) or short photoperiod (LD8:16). Sensitivity to light was increased in the second 8 h after L/D by LD8:16. Sensitivity to dark was increased in the first 8 h after L/D by LD16:8.

Xenopus tadpole melanophores are controlled by dark and light and melatonin without influence of time of day

Melanophores were studied in tadpoles of the South African clawed toad, Xenopus laevis, during the first week after hatching (stages 46-49) at 25 degrees C. The tadpoles had melanophores with dispersed melanosomes in the light and punctate melanophores in the dark in LD 12:12. The melanophores remained punctate in constant dark and the melanosomes remained dispersed in constant light. Lights-out (in the light-time of LD 12:12) caused the melanophores to become punctate, which occurred more quickly than the dispersion of melanosomes, which commenced when the lights were turned on (in the dark-time of LD 12:12). Melanophores with dispersed melanosomes in tadpoles (in constant light) became punctate in response to a series of melatonin concentrations (0.2-5 ng/ml) in their bathing water irrespective of the time of day melatonin was administered. An image-analysis technique for assessing melanophore responses was tested.

Circadian rhythm in pineal N-acetyltransferase activity: rapid phase reversal and response to shorter than 24-hour cycles (IV)

N-Acetyltransferase (NAT) is an enzyme whose rhythmic activity in the pineal gland and retina is responsible for circadian rhythms in melatonin. The NAT activity rhythm has circadian properties such as persistence in constant conditions and precise control by light and dark. Experiments are reported in which chicks (Gallus domesticus), raised for 3 weeks in 12 h of light alternating with 12 h of dark (LD12:12), were exposed to 1-3 days of light-dark treatments during which NAT activity was measured in their pineal glands. (a) In LD12:12, NAT activity rose from less than 4.5 nmol/pineal gland/h during the light-time to 25-50 nmol/pineal gland/h in the dark-time. Constant light (LL) attenuated the amplitude of the NAT activity rhythm to 26-45% of the NAT activity cycle in LD12:12 during the first 24 h. (b) The timing of the increase in NAT activity was reset by the first full LD12:12 cycle following a 12-h phase shift of the LD12:12 cycle (a procedure that reversed the times of light and dark by imposition of either 24 h of light or dark). This result satisfies one of the criteria for NAT to be considered part of a circadian driving oscillator. (c) In less than 24-h cycles [2 h of light in alternation with 2 h of dark (LD2:2), 4 h of light in alternation with 4 h of dark (LD4:4), and 6 h of light in alternation with 6 h of dark (LD6:6)], NAT activity rose in the dark during the chicks' previously scheduled dark-time but not the previously scheduled light-time of LD12:12. In a cycle where 8 h of light alternated with 8 h of dark (LD8:8), NAT activity rose in both 8-h dark periods, even though the second one fell in the light-time of the prior LD12:12 schedule.(ABSTRACT TRUNCATED AT 250 WORDS)

Circadian rhythm resetting in sparrows: early response to doublet light pulses

Circadian responses were studied using the perching activity of house sparrows (Passer domesticus). The sparrows were subjected to single or double 4-hr light pulses (the single pulses or the second pulses of the doublets scanned 24 hr) in the first cycle after previous entrainment to a light-dark cycle (LD 12:12). The differences in times at which the birds commenced perch-hopping in LD 12:12 before the pulses and in the five cycles immediately following the pulses were determined (phase shifts). A 24-hr time profile for phase shifts in response to single light pulses replicated our previous study: Early-night pulses delayed the rhythm (-1.7 hr), while late-night pulses advanced the rhythm (+3.8 hr). After pretreatment with a light pulse that advanced the birds +2.7 hr, the resetting curve was advanced. There were no delays; the range of average shifts was +0.1 hr to +6.2 hr. After pretreatment with a light pulse that delayed the birds -1.7 hr, the resetting curve was delayed. Average delays as much as -1.1 hr and advances up to +2.1 hr were measured. The data for double pulses were interpreted from predictions made from single-pulse data.

Diurnal variation of cation pump enzyme activity in pineal and seven other rat brain regions

Adult female Long-Evans rats were maintained on an automatically regulated artificial lighting schedule of light:dark (L:D) 14.5:9.5 for 12 wk. After sacrifice at 0630, 1130, 1600, 1800, 2000, 2200, 0230, or 0400, the pineals were removed, weighed, and assayed for N-acetyltransferase (NAT), melatonin, Mg++-paranitrophenylphosphatase (pNPPase), and K-pNPPase activity. The brains were quickly dissected into the following areas: cerebellum, superior colliculi, inferior colliculi, visual cortex, auditory cortex, sensorimotor cortex, and the hypothalamic area around the suprachiasmatic nucleus. These regions were weighed and 10% sucrose homogenates were prepared for determinations of protein, Mg++-pNPPase, and K+-pNPPase activity. Pineal melatonin rose over six-fold from 144 +/- 70 pg/gland at 1130 to 981 +/- 173 pg/gland at 0230. Similarly, pineal NAT activity rose over 11-fold, from 119 +/- 12 pmol/gland/h to 1315 +/- 232 pmol/gland/h at the same times. K+-pNPPase activity rose by about two-thirds, from 133 +/- 12.8 nmol/gland/h to 224 +/- 22.3 nmol/gland/h from 1600 to 0230. However, when expressed per mg protein, these differences in pNPPase activity were not significant. There were no significant daily rhythms discernible in any of the seven other brain regions across these times. We conclude that cation pump enzyme activity varies only slightly with time in the rat brain and pineal gland, in spite of definite daily rhythms of pineal melatonin and NAT activity.

Sparrow circadian rhythm responses to rotated light-dark schedules

House sparrows, Passer domesticus, were individually subjected to light-dark regimens while their perching activity was continuously monitored. The sparrows resynchronized in 5 days when LD8:16 (8 hr of light alternating with 16 hr of dark) was advanced by 8 hr; however, the sparrows were 1.7 hr from resynchronization after 5 days when the schedule was delayed 8 hr. Sparrows subjected to two simultaneously presented light-dark schedules (rotated LD8:16 provided by one light source imposed together with LD12:12 provided by a second light source) did not ignore either cycle; instead the sparrows responded as to a sequence of photoperiods; they resynchronized the onsets of their activity with the first time of lights-on of the collective photoperiod provided by the two light sources.

Photoperiod modifies circadian resetting responses in sparrows

Circadian responses to photoperiod were studied in house sparrows (Passer domesticus) by subjecting them to 4-h light pulses and measuring the subsequent phases of their circadian rhythms. The direction and magnitude of phase shifts in response to 4-h light pulses following pretreatment with light-dark cycles (LD) 16:8 or LD 8:16 varied with time of day; advances (3.4 h) occurred when pulses were imposed in the late subjective night on both groups of birds; delays (-2.1 h) occurred when the pulses were imposed in the early subjective night on the LD 8:16 birds. The time profiles for responses to light pulses that scanned 24 h (phase-response curves) were modified by long and short photoperiod. Short photoperiod 1) increased amplitude (1.7 h), 2) increased time from the prior lights-out to the peak of advances (6 h), and 3) decreased the mean phase shift (0.9 h).