<p><strong>OBJECTIVES: </strong>To estimate the association between fluoroquinolone use and tendon injury in adolescents.</p>

<p><strong>METHODS: </strong>We conducted an active-comparator, new-user cohort study using population-based claims data from 2000 to 2018. We included adolescents (aged 12-18 years) with an outpatient prescription fill for an oral fluoroquinolone or comparator broad-spectrum antibiotic. The primary outcome was Achilles, quadricep, patellar, or tibial tendon rupture identified by diagnosis and procedure codes. Tendinitis was a secondary outcome. We used weighting to adjust for measured confounding and a negative control outcome to assess residual confounding.</p>

<p><strong>RESULTS: </strong>The cohort included 4.4 million adolescents with 7.6 million fills for fluoroquinolone (275 767 fills) or comparator (7 365 684) antibiotics. In the 90 days after the index antibiotic prescription, there were 842 tendon ruptures and 16 750 tendinitis diagnoses (crude rates 0.47 and 9.34 per 1000 person-years, respectively). The weighted 90-day tendon rupture risks were 13.6 per 100 000 fluoroquinolone-treated adolescents and 11.6 per 100 000 comparator-treated adolescents (fluoroquinolone-associated excess risk: 1.9 per 100 000 adolescents; 95% confidence interval -2.6 to 6.4); the corresponding number needed to treat to harm was 52 632. For tendinitis, the weighted 90-day risks were 200.8 per 100 000 fluoroquinolone-treated adolescents and 178.1 per 100 000 comparator-treated adolescents (excess risk: 22.7 per 100 000; 95% confidence interval 4.1 to 41.3); the number needed to treat to harm was 4405.</p>

<p><strong>CONCLUSIONS: </strong>The excess risk of tendon rupture associated with fluoroquinolone treatment was extremely small, and these events were rare. The excess risk of tendinitis associated with fluoroquinolone treatment was also small. Other more common potential adverse drug effects may be more important to consider for treatment decision-making, particularly in adolescents without other risk factors for tendon injury.</p>

<p><strong>BACKGROUND: </strong>While fluoroquinolones are commonly used in adults, the use in children has been low. Since 2000, there were 3 US Food and Drug Administration (FDA) Boxed warnings regarding fluoroquinolones (2008, 2013, and 2016). Our objective was to describe the use of fluoroquinolones in children and assess the impact of 3 recent FDA warnings on fluoroquinolone use.</p>

<p><strong>METHODS: </strong>From 2000 to 2018, we assessed claims for all outpatient prescription fills to measure the use of systemic fluoroquinolones and other broad-spectrum antibiotics in children  less than 18 years old in the MarketScan Commercial Claims and Encounters database. We describe demographics, indication for antibiotic, and clinical characteristics. To assess the impact of FDA warnings on fill rates, we conducted an interrupted time-series analysis.</p>

<p><strong>RESULTS: </strong>The cohort included 34.6 million unique beneficiaries less than 18 years old with 441 062 fluoroquinolone fills (5.5 fills per 1000 person-years). The fluoroquinolone fill rate was highest among children &gt; 11 years old. Urinary tract infection was the most common associated diagnosis (21.8%). Since 2008, the fluoroquinolone fill rate has declined. By the end of the study period in December 2018, in the (counterfactual) absence of the FDA warnings, fluoroquinolone fill rate would have been 7.5 (95% confidence interval [CI]: 5.2-9.7); however, the corresponding rate in observed data was 2.8 (95% CI: 1.7-3.9).</p>

<p><strong>CONCLUSIONS: </strong>Fluoroquinolone use was low compared with other common broad-spectrum antibiotics and declining trends over time were associated with FDA warnings, even though these warnings were not pediatric specific. Future work should assess the adverse events at issue in these warnings in children.</p>