Abstract: Research JAMA Internal Medicine | Original Investigation Efficacy and Safety of Hydroxychloroquine vs Placebo for Pre-exposure SARS-CoV-2 Prophylaxis Among Health Care Workers A Randomized Clinical Trial Benjamin S. Abella, MD, MPhil; Eliana L. Jolkovsky, BA; Barbara T. Biney, MPH; Julie E. Uspal, MD; Matthew C. Hyman, MD, PhD; Ian Frank, MD; Scott E. Hensley, PhD; Saar Gill, MD, PhD; Dan T. Vogl, MD, MSCE; Ivan Maillard, MD, PhD; Daria V. Babushok, MD; Alexander C. Huang, MD, PhD; Sunita D. Nasta, MD; Jennifer C. Walsh; E. Paul Wiletyo, PhD; Phyllis A. Gimotty, PhD; Michael C. Milone, MD, PhD; Ravi K. Amaravadi, MD; and the Prevention and Treatment of COVID-19 With Hydroxychloroquine (PATCH) Investigators Visual Abstract IMPORTANCE Health care workers (HCWs) caring for patients with coronavirus disease 2019 Supplemental content (COVID-19) are at risk of exposure to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Currently, to our knowledge, there is no effective pharmacologic prophylaxis for individuals at risk. OBJECTIVE To evaluate the efficacy of hydroxychloroquine to prevent transmission of SARS-CoV-2 in hospital-based HCWs with exposure to patients with COVID-19 using a pre-exposure prophylaxis strategy. DESIGN, SETTING, AND PARTICIPANTS This randomized, double-blind, placebo-controlled clinical trial (the Prevention and Treatment of COVID-19 With Hydroxychloroquine Study) was conducted at 2 tertiary urban hospitals, with enrollment from April 9, 2020, to July 14, 2020; follow-up ended August 4, 2020. The trial randomized 132 full-time, hospital-based HCWs (physicians, nurses, certified nursing assistants, emergency technicians, and respiratory therapists), of whom 125 were initially asymptomatic and had negative results for SARS-CoV-2 by nasopharyngeal swab. The trial was terminated early for futility before reaching a planned enrollment of 200 participants. INTERVENTIONS Hydroxychloroquine, 600 mg, daily, or size-matched placebo taken orally for 8 weeks. MAIN OUTCOMES AND MEASURES The primary outcome was the incidence of SARS-CoV-2 infection as determined by a nasopharyngeal swab during the 8 weeks of treatment. Secondary outcomes included adverse effects, treatment discontinuation, presence of SARS-CoV-2 antibodies, frequency of QTc prolongation, and clinical outcomes for SARS-CoV-2–positive participants. RESULTS Of the 132 randomized participants (median age, 33 years [range, 20-66 years]; 91 women [69%]), 125 (94.7%) were evaluable for the primary outcome. There was no significant difference in infection rates in participants randomized to receive hydroxychloroquine compared with placebo (4 of 64 [6.3%] vs 4 of 61 [6.6%]; P > .99). Mild adverse events were more common in participants taking hydroxychloroquine compared with placebo (45% vs 26%; P = .04); rates of treatment discontinuation were similar in both arms (19% vs 16%; P = .81). The median change in QTc (baseline to 4-week evaluation) did not differ between arms (hydroxychloroquine: 4 milliseconds; 95% CI, −9 to 17; vs placebo: 3 milliseconds; 95% CI, −5 to 11; P = .98). Of the 8 participants with positive results for SARS-CoV-2 (6.4%), 6 developed viral symptoms; none required hospitalization, and all clinically recovered. CONCLUSIONS AND RELEVANCE In this randomized clinical trial, although limited by early termination, there was no clinical benefit of hydroxychloroquine administered daily for 8 weeks as pre-exposure prophylaxis in hospital-based..