Background: Hospitalised patients receiving intravenous antimicrobial therapy require a reliable device through which this is delivered. Short peripheral intravenous catheters (PIVCs) are the default device for antimicrobial therapy but up to half fail before therapy completion, leading to suboptimal drug dosing, patient distress from repeated insertions, and increased healthcare costs. This study will investigate the use of long PIVCs to determine if they are more reliable at delivering antimicrobial therapy. Methods: A two-arm, parallel randomised controlled trial of hospitalised adults requiring at least 3 days of peripherally compatible intravenous antimicrobials. Participants will be randomised to a short (<4 cm) or long (4.5-6.4 cm) PIVC. After interim analysis ( n=70) for feasibility and safety, 192 participants will be recruited. Primary outcome is disruption to antimicrobial administration from all-cause PIVC failure. Secondary outcomes include: number of devices to complete therapy, patient-reported pain and satisfaction, and a cost analysis. Ethical and regulatory approvals have been received.