Only the study team can determine whether someone qualifies for participation.
Inclusion criteria
- Must have cellulitis as defined here:
- Definition A (preferred definition):
Recent onset of soft tissue erythema, considered by the treating clinician to be bacterial in origin, and associated with signs of infection that include at least two of the following: pain, swelling, warmth, fever, lymphangitis, induration, or ulceration.
- Definition B (ONLY for darkly-pigmented subjects who cannot use Definition A):
Recent onset of soft tissue color change, pain, or swelling, considered by the treating clinician to be bacterial in origin, and at least one of the following: warmth, fever, induration, or ulceration
- Clinical (non-research) attending physician agrees with treatment with cephalexin until 3 days after all symptoms gone, using our weight-based dosing
- Responsible clinical attending physician comfortable with adding trimethoprim-sulfamethoxazole vs. placebo to the above
- Subject understands the study and signs written informed consent.
- Subject agrees to drink at least 1 liter of fluid per day.
- Subject will commit to all follow-up appointments
Exclusion criteria
- Age < 12 months or weight <15 kg
- Current skin infection has already been treated
- Allergy to sulfa drugs
- History of severe allergic reaction to penicillin (defined as anaphylactoid reaction, angioedema, bronchospasm)
- Current use of any antibiotic (other than topicals)
- Diabetes mellitus
- Cellulitis complicated by underlying peripheral vascular disease
- Renal insufficiency, defined as patient report, clinical suspicion, or creatinine>1.3 or EGFR<60 on the last-available set of chemistry results in our computer system
- Hospital admission required
- Presence of > 1 cc of purulent discharge at any time
- Cellulitis involving an indwelling vascular, enteric, or urinary catheter
- Immunocompromise of any etiology
- Pregnancy
- Breast feeding
- Facial cellulitis (infection is above the clavicles)
- Cellulitis associated with marine or freshwater injury, or animal or human bite. (Insect bites not excluded.)
- History of glucose-6-phosphate dehydrogenase deficiency
- Taking coumadin (warfarin), methotrexate, cisapride, phenytoin (dilantin), digoxin, or dofetilide
- Known megaloblastic anemia due to folate deficiency.
