Cephalexin 1000mg TID Matches 500mg QID for Uncomplicated Cellulitis

Adults with uncomplicated lower-extremity cellulitis who were prescribed cephalexin 1000mg three times daily (TID) had treatment failure rates similar to those prescribed 500mg four times daily (QID). The findings come from a retrospective cohort study published in Open Forum Infectious Diseases.

The authors noted that QID dosing can be burdensome and that published literature suggests more frequent dosing reduces adherence. They added that some clinicians have moved to prescribing 1000mg TID to improve feasibility and adherence, but that no published data directly compare the 2 regimens for uncomplicated cellulitis in adults.

The multicenter study included 300 adults (150 per group) treated for 5 to 10 days at Trinity Health Michigan primary care offices, urgent care centers, and emergency departments between January 2021 and September 2025. The primary outcome was treatment failure. This was defined as a composite of switching antibiotics because of documented lack of improvement or an intolerable adverse reaction, or retreatment for cellulitis within 30 days of completing therapy. Treatment failure occurred in 6.7% of the QID group and 5.3% of the TID group (P = .627). Median time to failure was 7 days in the QID group and 5 days in the TID group.

No patients in the QID group had a documented adverse drug reaction, while 1 patient in the TID group had mild gastrointestinal upset. No patients had documented nonadherence, Clostridioides difficile infection, or hospital admission related to cellulitis progression within 30 days. In the adjusted model, none of the evaluated variables, including TID dosing, was independently associated with treatment failure.

The authors concluded that 1000mg TID was well tolerated and as effective as 500mg QID, and that a thrice-daily strategy may improve adherence. However, they noted that because fewer patients than expected had treatment failure, the study may be underpowered to detect a difference between groups. The retrospective design also depended on medical record documentation. Excluding patients with a body mass index of 35 kg/m² or higher limits how widely the results apply.

Source: Ruiter ET, Eid KM, Kiebach AM, Harven LT, Jameson AP, Dumkow LE. Cephalexin 500 mg four times daily vs. 1000 mg three times daily for the treatment of uncomplicated cellulitis. Open Forum Infect Dis. Published online ahead of print. doi:10.1093/ofid/ofag681