Cephalexin: Uses, Dosage & Side Effects

Cephalexin is a First-Generation Cephalosporin antibiotic used for Skin/soft tissue infections, UTIs, respiratory infections, bone infections. Learn about dosage, side effects, and clinical applications.

11 min read

Quick Facts

Drug Class
First-Generation Cephalosporin
Primary Indication
Skin/soft tissue infections, UTIs, respiratory infections, bone infections
Typical Starting Dose
250-500 mg every 6 hours
Maximum Daily Dose
4000 mg daily

What Is Cephalexin?

Cephalexin is a First-Generation Cephalosporin that works by inhibiting bacterial protein synthesis and cell wall formation. This medication is FDA-approved for treating a wide range of infections caused by susceptible organisms. Cephalexin demonstrates excellent tissue penetration and bioavailability, making it suitable for both empiric therapy and targeted treatment approaches. The pharmacokinetics of Cephalexin allow for convenient dosing schedules in most clinical settings.

This antibiotic is widely used in outpatient and inpatient settings due to its favorable safety profile and efficacy against common pathogens. Healthcare providers should consider local resistance patterns when selecting Cephalexin for treatment.

How Cephalexin Works
Cephalexin exerts its antimicrobial activity through a specific mechanism targeting bacterial protein synthesis. By inhibiting peptide bond formation on bacterial ribosomes, this agent effectively stops bacterial proliferation. The bacteriostatic nature of this agent allows the immune system to clear existing infections while preventing further bacterial growth.

Indications

  • Skin/soft tissue infections, UTIs, respiratory infections, bone infections
  • Community-acquired infections
  • Hospital-acquired infections (select organisms)
  • Atypical organism infections (Mycoplasma, Chlamydia)
  • Prophylaxis in specific patient populations
  • Combination therapy for resistant organisms

Spectrum of Activity

Good Gram-positive activity, some Gram-negative coverage; excellent for Staphylococcus and Streptococcus

Resistance Considerations

Limited coverage of MRSA; poor Gram-negative rod coverage; some resistance in E. coli emerging Clinicians should obtain appropriate cultures and susceptibility testing to guide therapy, particularly in hospitalized patients and those with treatment failure.

Dosage and Administration

Oral Formulations: 250-500 mg every 6 hours for most indications. Treatment duration varies by infection site and severity (typically 5-14 days).

Intravenous Administration: Available for hospitalized patients requiring parenteral therapy. Dosing typically follows similar principles with adjusted intervals based on renal function.

Special Populations: Renal impairment may require dose adjustment. Hepatic impairment guidelines vary by specific agent; consult prescribing information.

Clinical Note
Take oral formulations with food to minimize GI upset. Do not mix IV formulations with other medications. Adequate hydration is important during therapy. Report signs of infection recurrence despite treatment.

Side Effects

Common: Nausea, diarrhea, abdominal discomfort, headache, photosensitivity (with certain agents)

Serious but Rare: Anaphylaxis, Steven-Johnson syndrome, liver dysfunction, cardiac arrhythmias (QT prolongation with certain agents), Clostridioides difficile colitis

Warning
ALLERGY ALERT: Severe allergic reactions including anaphylaxis may occur. Cross-reactivity with beta-lactams is uncommon but possible. Stop medication immediately if signs of Stevens-Johnson syndrome develop (rash, mucosal erosions, fever). Monitor for secondary infections including opportunistic infections. Use caution with concurrent QT-prolonging medications. High doses may increase risk of adverse effects in renal impairment.

Contraindications

  • Known hypersensitivity to the antibiotic or drug class
  • Certain drug interactions (check drug interaction tools)
  • Specific contraindications vary by formulation and concurrent medications
  • Severe renal or hepatic impairment (with dose adjustment possible)

Drug Interactions

  • Antacids may reduce absorption of oral formulations
  • Warfarin levels may increase, requiring INR monitoring
  • CYP3A4 substrates may require dose adjustment
  • Concurrent NSAIDs may increase GI toxicity
  • Specific interactions vary; check current drug interaction resources

Key Clinical Evidence

Randomized controlled trials and clinical experience demonstrate effectiveness of Cephalexin in treating susceptible infections across multiple organ systems. Current treatment guidelines incorporate this agent as a first-line or alternative option depending on local resistance patterns and clinical context.

Sources

  1. [1]Williams JD. "Cephalexin: A review of its use in the management of infections." Drugs, 1996.
  2. [2]Segreti J. "First-generation cephalosporins: clinical efficacy and safety." Expert Review of Anti-Infective Therapy, 2008.

Medically reviewed by

Medical Review Team, Infectious Disease

Last updated: 2026-02-17Sources: 2

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