RATIONALE & OBJECTIVE: Some drugs prescribed for chronic kidney disease (CKD) may become hazardous on sick days with volume depletion by increasing the risk of acute kidney injury (AKI) and kidney function loss; however, the risks and benefits of their use during intercurrent illness is unknown. STUDY DESIGN: 6-month pragmatic trial examining a sick-day protocol to determine if withholding prespecified drugs during a volume-depleting illness reduces the incidence AKI or kidney function loss in CKD. SETTING & PARTICIPANTS: 315 veterans with stage 3-5 CKD, treated with a renin-angiotensin-aldosterone inhibitor blocker, diuretic, nonsteroidal anti-inflammatory drug, or metformin were randomized into the study with n = 159 and n = 156 in sick-day protocol and usual care groups, respectively. INTERVENTION: Sick-day protocol administered via interactive voice response system (IVRS) or usual care with 6-month follow-up. OUTCOMES: The outcomes of the study are as follows: (1) Change in kidney function, (2) incidence of AKI based on International Classification of Diseases, Tenth Revision codes and ambulatory laboratory testing, (3) urgent service utilizations, and (4) sick days. RESULTS: The mean age was 70.1 ± 7.4 and 69.2 ± 8.1 years, with a mean baseline glomerular filtration rate (GFR) of 43.1 ± 13.1 and 43.8 ± 13.0 mL/min/1.73 m2, and 112 (70%) and 100 (64%) of participants with diabetes in the sick-day protocol and usual care groups, respectively. The mean change in GFR in the sick-day protocol and usual care groups from baseline to 6-month follow-up, adjusting for baseline GFR, was -0.71 (95% CI, -2.11 to 0.69) and -0.72 (95% CI, -2.12 to 0.68), respectively, with no significant difference, P = 0.99. Hospitalizations in the sick-day protocol and usual care groups were 11.5/100 and 8.4/100 events per person-months, respectively, with the adjusted rate ratio not significantly increased (prevalence ratio, 1.30; 95% CI, 0.96-1.76). Participants interacted with the IVRS in 81% of expected weeks and 19 had one or more qualifying events. In 33 true sick days, participants correctly followed the protocol in only 14. LIMITATIONS: Low incidence of sick days over the 6-month period of the study. CONCLUSIONS: The sick-day protocol was not associated with a significant reduction in AKI episodes or kidney function loss in a high-risk CKD population. Engagement with the IVRS was high, but successful implementation of the sick-day protocol was not optimal. TRIAL REGISTRATION: ClinicalTrials.gov; NCT03141905.