AHA Abx Prophylaxis Guidelines Hit Moderate-Risk Target

Patrice Wendling

May 10, 2019

The 2007 American Heart Association (AHA) guideline revision is reducing antibiotic prophylaxis among patients at moderate risk for infective endocarditis (IE), as intended, but is not driving the recent surge in hospitalizations for these life-threatening infections, according to a Canadian analysis.

Antibiotic prescribing prior to dental procedures tumbled by more than 40% in moderate-risk patients, with the mean quarterly rate of prescriptions dropping from 30,680 to 17,954 per million population in the periods before and after the guideline release (= .0004).

Prescribing rates dipped initially (P = .006) but then slowly increased (P = .01) among those at highest risk, the one group for which the AHA guidelines still recommend prophylaxis.

Change point analyses, however, identified an increase in new IE hospitalizations across all risk groups beginning in 2010, with rates ranging from 180 to 440 per million population for the moderate-risk group and from 336 to 1915 per million population for the highest-risk group.

"This time lag, along with the rise in IE incidence in both the high and moderate-risk groups suggests that this observed increase in endocarditis is likely unrelated to the change in the prescribing practice of antibiotic prophylaxis," Pallav Garg, MBBS, MSc, Western University, London, Canada, and colleagues write in the study, which was published April 26 in Circulation.

The investigators used multiple healthcare databases to identify prophylaxis prescriptions and IE-related hospitalizations from 2002 to 2014 in the province of Ontario.

High-risk patients (n = 1324) included those with previous IE, prosthetic valve replacement or prosthetic material used in valve repair, and certain forms of congenital heart disease. Moderate-risk patients (n = 455) included those with acquired valvular heart disease, hypertrophic cardiomyopathy, and other congenital cardiac malformations.

Over the study period, there were 7551 new hospitalizations for IE among 6884 adults. The average length of stay remained static, at 30.7 days.

Garg told theheart.org | Medscape Cardiology that the reasons for the increase in IE hospitalizations are unclear, but that it may be due to different risk profiles within patient groups, which were stratified by age.

"In the older-age group, perhaps we're seeing it because of other comorbidities and increasing rates of valve replacement and valve repair, and in the younger population, perhaps it is related, at least partly, to intravenous drug use," he said. "But that was not the focus of our study and is hypothesis-generating and should be investigated further."

Rates of valve replacement and repair increased among patients 65 years and older from 23.4% and 2.2% during the 2002 to 2006 period to 30.7% and 5.0% during the 2011 to 2014 period (P < .001 for both) but were unchanged among those aged 18 to 64 years. Comorbidities such as diabetes, chronic kidney disease, hypertension, and dialysis also increased over time among older patients.

Because the databases did not have ICD-9 or ICD-10 codes for intravenous (IV) drug use, the team used history of drug abuse, mental disorder, and hepatitis C as surrogates. Rates of these surrogates increased over time in the younger group but declined or remained steady in the older group.

Of note, Staphylococcus aureus, which is associated with injection drug use, was the most common pathogen (37.7%) in the younger group and increased dramatically over the study period (20% - 43%; P < .0001) as Streptococcal infection declined (31% - 20%; P = .007).

Among the older group, Streptococcal species accounted for most of the IE episodes (29%) and did not change significantly over time.

Given that the primary purpose of giving antibiotics prior to dental procedures is to prevent streptococcal infection, these findings provide further support that the increase in IE is unrelated to the change in antibiotic prophylaxis prescribing, Garg observed.

Although it is generally agreed that the 50-year practice of recommending prophylaxis to prevent endocarditis lacked solid evidence, studies examining the effects of the AHA guidelines in North America have yielded conflicting results. Data from the Nationwide Inpatient Sample showed steady increases in the incidence of IE from 2000 to 2011 and in IE due to Streptococcal species. Other population-based studies, however, have found no evidence of increased IE coinciding with the guidelines.

Although the present study showed prescriptions for moderate-risk patients fell quickly within the first two quarters after the 2007 guidelines, Garg noted that educational campaigns may be useful, as there were still 20,000 prescriptions per million population given between 2008 and 2014.

"It was quite surprising to see that there was this rather rapid uptake by a number of physicians and dentists, however, this uptake wasn't complete and we're still seeing a significant number of prescriptions being given to this moderate-risk population," he said.

Most of the prescriptions were issued by dentists or dental surgeons (78%), followed by general practitioners (17%), the authors report.

The study was supported by the Institute for Clinical Evaluative Sciences (ICES) Western site. Core funding for ICES Western is provided by the Academic Medical Organization of Southwestern Ontario (AMOSO), the Schulich School of Medicine and Dentistry, Western University, and the Lawson Health Research Institute. Garg was supported by the ICES Western Faculty Scholars Program and Opportunity Fund of the Academic Health Sciences Centre Alternative Funding Plan of AMOSO.

Circulation. Published online April 26, 2019. Abstract

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