Cefalexin is a first generation cephalosporin.

Dosage

• For uncomplicated urinary tract infections: prescribe cefalexin 250 mg every 6 hours, or 500 mg every 12 hours.
• For treatment of symptomatic or asymptomatic urinary tract infections (UTIs) in pregnancy, a 7-day course is recommended.
• For further information, see Screening for and managing asymptomatic bacteriuria in pregnancy and Managing suspected acute cystitis during pregnancy.

Contraindications and precautions

• Cefalexin should not be taken by people with known allergy to the cephalosporin group of antibiotics.
• Cephalosporins should given cautiously to penicillin-sensitive people. The British National Formulary advises that about 10% of penicillin-sensitive people will also be allergic to cephalosporins [BNF 57, 2009].
• The Health Protection Agency advises that broad spectrum antibiotics (such as co-amoxiclav, quinolones, and cephalosporins) should be avoided when narrow spectrum antibiotics remain effective, as they increase risk of Clostridium difficile, meticillin-resistant Staphylococcus aureus (MRSA), and resistant UTIs [HPA, 2009].

Use in pregnancy and breastfeeding

• Although cefalexin is not licensed in these groups, the manufacturer reported no evidence of teratogenicity in clinical studies [ABPI Medicines Compendium, 2005].
• Cephalosporins (such as cefalexin) can be used in women who are pregnant or breastfeeding [Schaefer et al, 2007].

Adverse effects

• Gastrointestinal adverse effects (such as nausea, vomiting, and diarrhoea), are commonly reported.
• The manufacturer of cefalexin advises that pseudomembranous colitis should be considered in people who develop antibiotic-associated diarrhoea [ABPI Medicines Compendium, 2005]. It can be mild, or can be life threatening. Mild cases of pseudomembranous colitis usually respond to drug discontinuation alone.

Drug interactions

• Contraceptives: antibiotics may cause the combined oral contraceptive pill or patch to fail during the first few weeks of treatment [Baxter, 2006] (see the sections on Antibiotics and Drug interactions in the CKS topic on Contraception for information on the combined oral contraceptive pill or patch):
• Advise women to use additional contraception during the course of treatment and for 7 days afterwards. If this 7-day period runs beyond the end of the pack of contraceptive pills, advise the woman to start a new pack without a break (omitting any inactive tablets) [FFPRHC, 2005; FFPRHC, 2007].
• Anticoagulants: documented reports of oral anticoagulant/penicillin (including amoxicillin) interaction are relatively rare [Baxter, 2006]. However, the British National Formulary advises that common experience in anticoagulant clinics is that a course of broad spectrum penicillin can alter the international normalized ratio [BNF 57, 2009].

[ABPI Medicines Compendium, 2005; BNF 57, 2009]