Cefalexin (UTI / GBS Prophylaxis in Pregnancy)

How it works

It binds penicillin-binding proteins and inhibits bacterial cell-wall peptidoglycan cross-linking, producing a bactericidal effect against susceptible Gram-positive and many Gram-negative organisms.

Prescribing in practice

• Avoid in patients with a history of immediate or severe hypersensitivity to penicillins or cephalosporins; the risk of cross-reactivity is low but clinically significant reactions can occur.
• Cefalexin is considered suitable in all trimesters of pregnancy and during breastfeeding, making it a useful option for UTI and group B streptococcus cover.
• Confirm susceptibility on culture where possible, as resistance among urinary coliforms is common.

Monitoring

Routine laboratory monitoring is not required, but review the clinical response and any culture and sensitivity results, and watch for signs of antibiotic-associated diarrhoea.

Counselling the patient

• Complete the full prescribed course even if symptoms settle quickly.
• Report severe or persistent diarrhoea, which may indicate Clostridioides difficile infection.
• Seek urgent advice for any rash, swelling or breathing difficulty after a dose.

Evidence & guidelines

Cefalexin is a long-established cephalosporin with a reassuring safety record in pregnancy and is widely recommended for UTI and as an alternative for group B streptococcus prophylaxis.