ImportanceMidline catheters (MCs) are widely used, but safety and efficacy compared with peripherally inserted central catheters (PICCs) has not been adequately evaluated.ObjectiveTo compare the safety and efficacy of MCs with PICCs among adult patients with an anticipated intravenous therapy lasting from 5 to 28 days.Design, Setting, and ParticipantsThis parallel, 2-group, open-label, randomized clinical trial (RCT) was conducted in Denmark from October 2018 to February 2022 at a single academic tertiary care center. Adult inpatients and outpatients were consecutively randomized.InterventionPatients were randomized in a 1:1 ratio to either the MC group or the PICC control group.Main Outcomes and MeasuresThe primary outcome was catheter-related bloodstream infection (CRBSI), analyzed using the Fisher exact test. Secondary outcomes were symptomatic catheter-related thrombosis and catheter failure, including mechanical cause, phlebitis, infiltration, pain in relation to drug or fluid administration, and leaking from the puncture site. Incidence rate ratios (IRRs) were calculated to assess between-group failure rates over device dwell time using Poisson regression. An intention-to-treat analysis was performed.ResultsA total of 304 patients (mean [SD] age, 64.6 [13.5] years; 130 [42.8%] female) were included in the analysis, and 152 patients were allocated to each catheter group. The incidence of CRBSI was low, with 0 in the MC group and 1 in the PICC control group (Pâ>â.99). The MC group had a higher catheter-related complication rate (20 [13.2%] vs 11 [7.2%]), and an IRR of 2.37 (95% CI, 1.12-5.02; Pâ=â.02) for complications compared with the PICC control group. In a post hoc analysis stratified by catheter dwell time, no significant difference in complication rate (IRR, 1.16; 95% CI, 0.50-2.68; Pâ=â.73) was found between the 2 groups for catheters used less than 16 days.Conclusions and RelevanceIn this RCT with patients who received medium- to long-term intravenous therapy, the incidence of CRBSI was low, with no difference between MCs and PICCs. The use of MCs resulted in a higher incidence of catheter-related complications compared with use of PICCs. This finding should be balanced in the decision of type of catheter used at the individual patient level.Trial RegistrationClinicalTrials.gov Identifier: NCT04140916