Cefalexin – First-generation cephalosporin antibiotic for common infections.
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What is Cefalexin?
Cefalexin is a first-generation cephalosporin antibiotic that’s particularly effective for skin, soft tissue, and urinary tract infections. It’s often chosen as an alternative to penicillins or when broader spectrum coverage is needed for common bacterial infections.
Book an online consultation if you’re experiencing symptoms of bacterial infections such as skin infections, UTI symptoms, or persistent respiratory infections. Our GPs can assess your symptoms and determine if Cefalexin is the appropriate antibiotic for your specific condition.
What is Cefalexin used for?
- Skin and soft tissue infections
- Urinary tract infections (UTIs)
- Respiratory tract infections
- Bone and joint infections
- Dental infections
- Post-surgical infection prevention
- Cellulitis and wound infections
- Streptococcal throat infections
How does Cefalexin work?
A beta-lactam antibiotic that inhibits bacterial cell wall synthesis by binding to penicillin-binding proteins, causing bacterial cell death. Effective against many gram-positive bacteria.
Dosage and Administration
Adults
250-500 mg taken 4 times daily, or 500 mg-1 g twice daily. Treatment usually 5-10 days.
Children
25-50 mg per kg daily in divided doses—GP will calculate appropriate dose based on weight.
Important Notes
- Take at evenly spaced intervals throughout the day.
- Can be taken with or without food.
- Complete the full course even if symptoms improve.
- Take with food if it upsets your stomach.
Side Effects
Common Side Effects
- Nausea and vomiting
- Diarrhoea
- Stomach pain
- Skin rash
- Vaginal thrush (in women)
- Headache
Serious Side Effects
Seek immediate medical attention if you experience:
- Severe allergic reactions (especially if allergic to penicillins)
- Severe diarrhoea (C. difficile infection)
- Stevens-Johnson syndrome (severe skin reaction)
- Blood disorders (rare)
- Kidney problems (rare)
Important Warnings
- Tell your GP if you're allergic to penicillins—about 10% of people with penicillin allergy also react to cephalosporins.
- Complete the full course to prevent antibiotic resistance.
- Tell your GP if you have kidney problems—dose adjustment may be needed.
- Stop and seek medical attention if you develop severe diarrhoea or skin rash.
- Generally well-tolerated with fewer side effects than many antibiotics.
Drug Interactions
Tell your GP if you're taking any of the following medications:
- Warfarin—may increase bleeding risk, monitor INR more frequently.
- Metformin—may increase metformin levels in people with kidney problems.
- Probenecid—may increase cefalexin levels.
- Live vaccines—may reduce vaccine effectiveness.
- Generally fewer drug interactions than many other antibiotics.
Frequently Asked Questions
How is Cefalexin different from Amoxicillin?
Cefalexin is a cephalosporin while Amoxicillin is a penicillin. Cefalexin may be used when penicillins aren't suitable or for infections resistant to penicillins.
Can I take Cefalexin if I'm allergic to penicillin?
There's about a 10% chance of cross-reaction. Your GP will assess the severity of your penicillin allergy and may prescribe it with caution or choose an alternative.
Why do I need to take it four times a day?
Cefalexin has a shorter half-life, so taking it 4 times daily (every 6 hours) maintains effective antibiotic levels in your body throughout the day.
Can Cefalexin treat all types of infections?
No, it's mainly effective against gram-positive bacteria and some gram-negative bacteria. Your GP will choose it based on the likely bacteria causing your infection.
Medically Reviewed by: Mohammed Hassan - Independent Prescriber
Last Updated: 2025-01-14