Cefalexin

1. Introduction

Cefalexin (also spelled cephalexin), marketed under brand names such as Keflex and Ceporex, is a first-generation cephalosporin antibiotic. It is widely used to treat bacterial infections of the respiratory tract, skin, soft tissues, urinary tract, and bones. It works by inhibiting bacterial cell wall synthesis, leading to bacterial cell death.

2. Indications

  • Approved Indications:
    • Respiratory tract infections (e.g., pharyngitis, sinusitis, bronchitis).
    • Skin and soft tissue infections (e.g., cellulitis, abscesses, impetigo).
    • Urinary tract infections (UTIs).
    • Bone infections (osteomyelitis).
    • Otitis media.
  • Off-Label Uses:
    • Prophylaxis in dental procedures for patients with prosthetic heart valves (penicillin-allergic patients).

3. Dosage

  • Adults:
    • 250–500 mg every 6–8 hours (maximum: 4 g/day).
  • Children:
    • 25–50 mg/kg/day in divided doses every 6–8 hours (maximum: 4 g/day).
  • For Severe Infections:
    • Up to 1 g every 6 hours.
  • Urinary Tract Infections:
    • Adults: 500 mg every 12 hours.
    • Children: 25–50 mg/kg/day in divided doses.

4. Administration

  • Take orally with or without food.
  • To minimise gastrointestinal upset, take with food.
  • Shake the suspension well before each use.

5. Forms Available

  • Capsules: 250 mg, 500 mg.
  • Oral suspension: 125 mg/5 mL, 250 mg/5 mL.
  • Tablets: 500 mg.

6. Side Effects

6.1. Common Side Effects

  • Nausea.
  • Diarrhoea.
  • Abdominal pain.
  • Skin rash.

6.2. Less Common Side Effects

  • Headache.
  • Dizziness.

6.3. Rare but Serious Side Effects

  • Severe allergic reactions (e.g., anaphylaxis, angioedema).
  • Clostridioides difficile-associated diarrhoea.
  • Stevens-Johnson syndrome.

7. Warnings

  • Use with caution in patients with a history of penicillin allergy, as cross-reactivity may occur.
  • Prolonged use may result in superinfection, including fungal overgrowth or resistant bacteria.

8. Precautions

  • Monitor for signs of an allergic reaction, particularly in patients with a known beta-lactam allergy.
  • Use with caution in patients with renal impairment, as dose adjustments may be necessary.
  • Avoid unnecessary use to reduce the risk of antibiotic resistance.

9. Interactions

  • Drug-Drug Interactions:
    • Metformin: Increased risk of lactic acidosis.
    • Probenecid: Increases cefalexin levels by reducing renal excretion.
    • Warfarin: May enhance anticoagulant effects, increasing bleeding risk.
  • Drug-Food Interactions:
    • No significant food interactions reported.

10. Monitoring Parameters

  • Resolution of infection symptoms (e.g., fever, pain, redness).
  • Monitor renal function in patients with pre-existing kidney disease.
  • Watch for signs of superinfection or severe diarrhoea.

11. Use in Children

  • Safe and effective in children; dosage should be adjusted based on weight and age.

12. Use in Pregnancy

  • Category B: Generally considered safe during pregnancy.
  • Should be used if clearly needed and prescribed by a healthcare provider.

13. Use in Elderly

  • Safe, but monitor renal function closely as elderly patients are more prone to renal impairment.

14. Use in Kidney Disease

  • Dose adjustments are required based on creatinine clearance.
  • For Creatinine Clearance <30 mL/min: 250–500 mg every 12 hours.

15. Use in Liver Disease

  • No specific dosage adjustments required; use with caution in severe hepatic impairment.

16. Patient Counselling Points

  • Complete the full course of treatment, even if symptoms improve early.
  • Take with food to minimise stomach upset.
  • Inform patients to contact their doctor immediately if they experience symptoms of an allergic reaction (e.g., rash, swelling, or difficulty breathing).
  • Advise against taking antidiarrhoeals if diarrhoea occurs without consulting a doctor.
  • Store the suspension in the refrigerator and discard after 14 days.

17. Table of Brand Names, Manufacturers, and Prices

Brand NameManufacturerPrice (USD)
KeflexEli Lilly$15–30 (30 capsules, 500 mg)
CeporexGSK$20–35 (30 capsules, 500 mg)
Generic OptionsVarious$10–20 (30 capsules, 500 mg)

18. FAQs (15 Questions)

  1. What is cefalexin used for?
    It is used to treat bacterial infections such as UTIs, respiratory tract infections, skin infections, and bone infections.
  2. How does cefalexin work?
    It inhibits bacterial cell wall synthesis, causing bacterial cell death.
  3. Can cefalexin treat viral infections?
    No, cefalexin is ineffective against viral infections such as the flu or common cold.
  4. How long does cefalexin take to work?
    Symptoms usually improve within 2–3 days, but the full course must be completed.
  5. What are the common side effects of cefalexin?
    Nausea, diarrhoea, abdominal pain, and skin rash.
  6. Can cefalexin be taken with food?
    Yes, it can be taken with or without food. Taking it with food may reduce stomach upset.
  7. Is cefalexin safe during pregnancy?
    Yes, it is generally considered safe during pregnancy when prescribed by a healthcare provider.
  8. Can children take cefalexin?
    Yes, it is safe for children when dosed appropriately based on weight and age.
  9. Does cefalexin interact with other medications?
    Yes, it may interact with metformin, probenecid, and warfarin.
  10. What should I do if I miss a dose?
    Take it as soon as you remember, but skip it if it’s close to the next dose. Do not double up.
  11. Can cefalexin cause diarrhoea?
    Yes, it can cause mild diarrhoea. However, severe diarrhoea may indicate a more serious condition, such as C. difficile infection.
  12. How should cefalexin be stored?
    Store capsules and tablets at room temperature. Refrigerate the suspension and discard after 14 days.
  13. What should I do if I experience an allergic reaction?
    Stop taking cefalexin and seek immediate medical attention.
  14. Is cefalexin available over the counter?
    No, cefalexin requires a prescription.
  15. Can cefalexin be used long-term?
    It is typically used for short-term treatment of infections. Long-term use may increase the risk of antibiotic resistance or superinfection.