Cephalexin (Keflex)
First-generation oral cephalosporin antibiotic. Good gram-positive coverage (staph, strep) and limited gram-negative activity. First-line for uncomplicated skin/soft tissue infections and UTIs. ~90% oral bioavailability, almost entirely renally eliminated unchanged. Generally well-tolerated with low cross-reactivity (~2%) in penicillin-allergic patients.
Projected serum levels — 500 mg, once daily
Maintenance schedule: 500 mg once daily (oral).
Modeled steady state after ~1 days: peak ≈ 230 mg, trough ≈ 0.000 mg body load. Population-based estimate over 15 days for a 500 mg dose at a 70 kg reference body mass — the interactive app scales curves to your doses, timing, and body mass.
Key facts
- Category
- Antibiotic
- Route modeled
- Oral
- Model confidence
- inferred
- Half-life
- 1 h
- Common dose
- 500 mg
- Suggested maximum
- 4k mg/day
- Reference dose range
- 250–4k mg (single dose)
- Suggested cadence
- once daily
- Validated against
- 500 mg oral — Cmax 18 mg/L at 1 h
Research behind this entry
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Cephalexin: a review of its antibacterial, pharmacokinetic and therapeutic properties
Comprehensive review confirming cephalexin half-life of 0.6-1.2 hours, 90% bioavailability, and establishing it as effective first-line therapy for skin infections, pharyngitis, and uncomplicated UTIs.
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Cross-reactivity and tolerability of cephalosporins in patients with penicillin allergy
Systematic review finding true cross-reactivity between penicillins and first-generation cephalosporins is ~1-2%, much lower than historically reported, supporting cephalexin use in most penicillin-allergic patients.
2 published studies referenced in the app, each with a plain-language summary.