Prior antibiotic use is a strong predictor of the pattern of changes in the risk of infection-related hospital admissions, a large UK population-based cohort study has found.
The study, published in BMC Medicine , analysed electronic health records from UK primary care linked to hospital admission records. The study population (1.8 million) included patients prescribed a systemic antibiotic, recent record of selected infections and no history of chronic obstructive pulmonary disease. Propensity-matched cohorts were identified based on quintiles of prior antibiotic use in the 3 years before.
Repeated antibiotic use was frequent. Amoxicillin (including co-amoxiclav) was the most frequently prescribed antibiotic although its use decreased in patients with higher prior antibiotic use. Use of clarithromycin, nitrofurantoin, and cephalexin increased with higher prior antibiotic use.
The level of prior antibiotic use was found to be a strong predictor of the pattern of changes in the risk of infection-related hospital admissions (mostly due to lower respiratory track illness or pneumonia) after antibiotic prescriptions.
The highest rates of hospital admissions for infection-related complications were observed shortly after antibiotic start in all prior exposure quintiles.
For patients with limited prior antibiotic use, rates then dropped quickly and substantially.
In contrast, reductions over time were substantially less in patients with frequent prior antibiotic use, with rates remaining elevated over the following 6 months.
In patients without comorbidity comparing the highest to lowest prior exposure quintiles in the Clinical Practice Research Databank, the IRRs were 1.18 [95% CI 0.90–1.55] in the first 3 days after prescription, 1.44 [95% CI 1.14–1.81] in the days 4-30 after, and 3.22 [95% CI 2.29–4.53] in the 3 to 6 months after.
A potential mechanism is that antibiotics may cause dysbiosis contributing to colonisation with resistant bacteria, suggested the researchers, advising that “antibiotics should be used judiciously and only periodically unless indicated.”