Antimicrobial-associated Organ Injury Among Older Adults: A Systematic Review and Meta-analyses Protocol

Background: Older adults (aged 65 years and above) constitute the fastest growing population cohort in the western world. There is increasing evidence that the burden of infections disproportionately affects older adults, and hence this vulnerable population is frequently exposed to antimicrobials. There is currently no systematic review summarising the evidence for risk of organ injury following antimicrobial exposure among older adults. This protocol will outline how we will conduct a systematic review and meta-analyses to examine the relationship between antimicrobial exposure and organ injury in older adults. Methodology: We will search for Psych INFO, PubMed, and EMBASE databases for relevant articles using MeSH terms where applicable. After removing duplicates, articles will be screened for inclusion into or exclusion from the study by two reviewers. Title and abstract screening will be done rst, followed by full-text screening. The Newcastle-Ottawa scale will be used to assess the risk of bias for cohort and case-control studies, and the Cochrane collaboration's tool will be used to assess the risk of bias for randomised control trials. We will explore the potential sources of heterogeneity and bias using funnel and forest plots of the included studies.

Discussion and registration: In this protocol, systematic review methods to identify relevant literature on antimicrobial exposure and associated organ injury have been described. The ndings from the review are intended to increase our understanding of the different types of antimicrobials associated with organ injury among older adults, therefore has the potential for improving the prescribing practice for this vulnerable population. This protocol is registered in the PROSPERO database (registration number CRD42020152621).

Background
Older adults aged 65 years and above comprise the fastest and largest expanding population age group in the developed world (1). They are prone to infectious diseases such as pneumonia, skin, and soft tissue infections (SSTI), urinary tract infections (UTI) and septicaemia when compared to younger people (1). It is estimated that the older adults comprise 48.7% of individuals who are admitted to hospital intensive care units for these infections (2), resulting in their increased length of hospital stay and exposure to antimicrobials. Giarratano et al. (3) highlighted several predisposing factors that make older adults more susceptible to antimicrobial adverse events. These include physiological changes, higher comorbidities, drug-drug interactions, drug delivery routes used, and length of time they are in contact or exposed to the antimicrobial agents. In one large prospective cohort study, antimicrobial related adverse events accounted for 19.3% of all drug-related adverse events seen at the emergency department (2). Several antimicrobial-associated adverse events become apparent several years after the drug has been approved, and the adverse events reported in clinical trials differ considerably from post-marketing surveillance. Since most clinical trials exclude older adults, the true nature and incidence of antimicrobial related adverse events in this population are unknown. In their review, Giarratano et al. (3) concluded that there is a general lack of epidemiological studies on antimicrobials used among the older adults, yet this is essential in informing healthcare providers to achieve optimal safety and effectiveness when providing antimicrobial pharmacotherapy to the older adults. A systematic review is much needed to synthesise the evidence given the potential for public health implications if antimicrobials are associated with organ injury in older adults. This paper describes a protocol for carrying out a systematic review and metaanalysis to investigate whether antimicrobial exposure is associated with kidney, liver, or tissue injury among older adults.

Methods And Design
This protocol was designed following the Preferred Reporting Items for Systematic Reviews and Metaanalysis (PRISMA) guidelines (4), and it is registered in the PROSPERO database (registration number CRD42020152621). The PRISMA-P checklist (5) was used to guide the presentation of the items of this protocol (additional le 1).

Review question
In this protocol, the procedures for a systematic review and meta-analysis that is intended to answer the question: "Is antimicrobial exposure among the over 65 associated with kidney, liver, or tissue injury?" have been outlined.
The components of the population, exposure, comparator, and outcome (PECO) are as follows: Population: Older adults aged 65 years and above Exposure: Any antimicrobial treatment, or long-term antimicrobial treatment, or broad-spectrum antimicrobial treatment Comparator: No antimicrobial treatment, or short-term antimicrobial treatment, or narrow-spectrum antimicrobial treatment.
Outcome: kidney, liver, or tissue injury during or soon after antimicrobial exposure.

Eligible study designs
This study will include all primary epidemiological observational studies, including cross-sectional studies, prospective cohort studies, retrospective cohort studies, case-control studies, and interventional studies that meet the inclusion criteria. However, very few randomised controlled trials are expected to be included in this study. Case reports, case series, reviews, commentaries, editorials, will not be included in this study.

Eligible participants
A study is eligible for this review if it reported exposure to antimicrobial agents among older adults of 65 years or above. Observational and interventional studies are eligible for inclusion in this study. However, studies reporting antimicrobial exposure to children or adults under 65 years of age will be excluded.
Studies reporting exposure of any age group to other medicines but not antimicrobials will also be excluded.

Exposures of interest
The exposure of interest is the therapeutic use of antimicrobials of any dose, class/type (narrow or broadspectrum), duration, or route given for any indication. The comparator is either a group that did not receive any antimicrobials or a group that received an antimicrobial or group of antimicrobials other than the exposure of interest.

Outcome measures of interest
The main outcome of this study is to determine whether antimicrobial exposure increases organ (liver, kidney, or tissue) injury following any antimicrobial exposure among older adults who are 65 years and above. The main measure of effect will be the relative risk (6) of organ injury among the exposed when compared to the unexposed populations. The incidence rate of organ (kidney, liver, or tissue) injury among the antimicrobial exposed group of the older adults will be compared with the respective incidence rate of the control groups (not exposed to antimicrobials) and expressed as risk ratios.
Additional outcome(s) Additional outcomes will include the determination of whether broad-spectrum antimicrobials increase the risk of organ injury when compared to the narrow spectrum, and whether prolonged exposure increases the risk when compared to short term exposure. The main measure of effect on both outcomes is the risk difference (7) between comparison groups. The risk of organ injury among participants who received broad-spectrum antimicrobials will be compared with those who received narrow-spectrum antibiotics. Secondly, the risk of organ injury among participants with prolonged exposure to antimicrobials will be compared with those on the short term. Risk difference will be the main measure of effect on both cases.
Search methods for the identi cation of studies Searches will be conducted in Psych INFO, PubMed and EMBASE databases. Restrictions to publication dates will be applied and limited to the English language. The full search strategy is described in appendix 1.

Selection of eligible studies
Search results from all databases will be uploaded into EndNote X9 (8) bibliographic software and manually de-duplicated. After removing duplicates, studies will be uploaded into Covidence (9) for the title and abstract screening, as well as full-text screening. Studies identi ed by the search strategy will be screened independently by two reviewers (TC and PN) using the titles and/or abstracts for their potential to meet the inclusion criteria described above. The full texts of potentially relevant studies will be retrieved and individually reviewed for eligibility using a standardised assessment tool. A decision process ow chart ( gure 1) has been developed to standardise full-text selection by both reviewers.
Where the two reviewers disagree, the opinion of the third reviewer (SR) will be sought. Further study information will be sought from the study authors about any missing data or clari cation about study participants and study outcomes.

Data extraction process
The data to be extracted include study name/article title, authors, journal and full reference, country, study design and setting, participant demographics, exposures (types of antimicrobials including dose, duration and route), a sample size of exposed and comparator groups, confounders, statistical methods, primary outcome, secondary outcomes, and participant missing data and reason for missing. Extracted participant demographics for exposure and control groups will include mean or median age at antimicrobial administration, sex, and ethnicity. For the primary or secondary study endpoints, wherever applicable, we will extract mean (plus standard deviation), median (plus interquartile range), number of cases, and relative risks (with 95% con dence intervals).

Risk of bias assessment for eligible studies
Each reviewer will critically appraise each study and perform the risk of bias using the appropriate tool. Risk of bias for randomised controlled trials (RCTs) will be assessed using version 2 of the Cochrane riskof-bias tool for randomised trials (RoB 2) (10). In contrast, the Newcastle-Ottawa tool (11) will be used to assess the risk of bias for observational studies. The quality assessment across the studies will be done using the Grading of Recommendations, Assessment, Development, and Evaluation (GRADE) tool (12) for each outcome. Where the two reviewers differ in opinion, the third reviewer's opinion will be sought. The authors will be contacted for additional information in case of missing or unequivocal information. The following domains will be assessed for the risk of bias: Confounders relevant to all or most of the studies Important confounding factors in this study are those that affect the association of antimicrobial exposure and organ injury among older adults. The severity of the disease being treated, comorbidities, and non-antimicrobial medication known to risk organ injury will be considered as signi cant confounders. Sex and age will be also be considered apriori.
Strategy for data synthesis Descriptive analysis of data All studies that meet the inclusion criteria will be described, including the following: 1. Study design -including the study quality, data collection methods, the validity of tools used and the statistical analysis 2. Participants (both exposed and unexposed) -including demographic and socio-economic characteristics and health status such as the severity of the disease.
3. Exposure -the types of antimicrobials used, duration and frequency of use and spectrum (broad or narrow) of effectiveness.
4. Outcomes -primary and secondary outcomes for each study will be described.

Statistical analysis
Meta-analysis for quantitative data will be carried out for only those observational studies scoring at least six on the Newcastle-Ottawa scale. The analysis will be done using the more recent version of the R statistical software (R i386 4.0.2). Results for studies that show enough homogeneity will be pooled together using the random-effects model. Relative risks, calculated at 95% con dence intervals and twosided p-values, will be used as the primary effect measure. If homogeneity is insu cient, quantitative results will be tabulated, and a narrative synthesis will be provided to summarise the results displayed in the included studies. Heterogeneity among the observational studies will be assessed using the Cochran's Q test (13) at a 5% signi cance level and quanti ed using the I 2 statistic (13). An I 2 value of more than 50% will be considered to re ect substantial heterogeneity and therefore will trigger sensitivity analysis to investigate the possible source of heterogeneity. For the results of the meta-analysis, publication bias will be assessed using a funnel plot (14). Details of each included study will also be presented in a table of study characteristics, from which exploratory, descriptive analyses will be done.

Analysis of subgroups or subsets
Subgroup analysis by age (65-80 years and more than 80 years), sex, ethnicity, type of organ damage and antimicrobial class will be carried out. Additional subgroups will be analysed, but it is not easy to specify them in advance.

Strategy for the presentation of results
For each database used, the nal search strategy, and any other additional searches done, will be provided in a different le. The process of selecting articles from title screening up to nal article inclusion into the nal review will be shown on a ow diagram following the PRISMA guidelines (4). Information about the rationale of exclusion during full article screening will be presented in this ow diagram. A funnel plot will be used to demonstrate any potential small study effects and potential publication bias for any meta-analysis with at least six studies (15). The characteristics of studies tables and meta-analyses results of this review will be compiled into a publishable journal article. Other information will be included by text, descriptive statistics, and a summary table of ndings. The GRADE tool (12) will be used to guide the construction of the summary of ndings table. The full results on the quality of individual study assessment using the Newcastle-Ottawa scale will be provided in the additional le. However, the summarised table of these ndings will be presented in the main article.

Ethical considerations
This systematic review and meta-analysis will not involve directly working with patients or human tissues. However, during the conduct of the review, ethical principles will still be observed to ensure integrity. Any potential con icts of interests will be declared, all contributors acknowledged, and plagiarised material will be included in the review (16).

Dissemination
The systematic review and meta-analysis will be submitted for publication in a peer-reviewed journal in geriatrics. The ndings will be presented at international conferences in the area of geriatrics or pharmacoepidemiology. This work will contribute to a PhD undertaken at the University of Bath. The results will be communicated to the patient and public engagement networks supported by the NHS Research and Development o ce, BSW (Bath, Swindon and Wiltshire).

Discussion
This protocol describes the method for the synthesis of current evidence related to antimicrobial exposure and organ injury among older adults aged 65 years or more. The proposed systematic review will probably be the rst to summarise the association of antimicrobial use and organ injury among older adults. We anticipate signi cant heterogeneity between the included studies, and we may not have enough studies to pool together to conduct a meta-analysis for each of the primary outcomes of interest. However, we may be able to generate evidence on the risk of antimicrobial exposure on organ injury as a composite measure. A clearer understanding of this relationship will unravel any information gaps, advance academic literature, and inform the development of antimicrobial prescribing policies for this vulnerable population.