First-generation oral cephalosporin Pregnancy: Although laboratory and clinical studies have shown no evidence of teratogenicity, caution should be exercised when prescribing for the pregnant patient. Caution should be exercised when administered to a nursing woman (risk of candidiasis and CNS toxicity to the neonate; theoretical possibility of later sensitisation).

Cefalexin

Brand names: Keflex

Cefalexin is an oral first-generation cephalosporin used for urinary tract, skin and soft tissue, and some respiratory tract infections.

Auto-extracted from the source labelling — not yet independently clinician-verified. These values were distilled from the UK SPC (or the US label where noted) but have not had a clinician sign-off. Confirm against the current SmPC before prescribing.

Adult dose

Dose: 500 mg every 8 hours (most infections); adult dosage range 1-4 g daily in divided doses

Route: Oral

Frequency: Every 8 hours

Max: If daily doses greater than 4 g are required, parenteral cephalosporins in appropriate doses should be considered

For skin and soft tissue infections, streptococcal pharyngitis and mild, uncomplicated urinary tract infections, the usual dosage is 250 mg every 6 hours, or 500 mg every 12 hours. For more severe infections or those caused by less susceptible organisms, larger doses may be needed. Elderly and patients with impaired renal function: as for adults; reduce dosage if renal function is markedly impaired.

Paediatric dose

Route: Oral

Frequency: In divided doses (see notes)

Usual recommended daily dosage for children is 25-50 mg/kg in divided doses. For skin and soft tissue infections, streptococcal pharyngitis and mild, uncomplicated UTIs, the total daily dose may be divided and given every 12 hours. Suggested schedule for most infections: children under 5 years, 125 mg every 8 hours; children 5 years and over, 250 mg every 8 hours. In severe infections the dosage may be doubled. In otitis media, a dosage of 75 to 100 mg/kg/day in 4 divided doses is required. For beta-haemolytic streptococcal infections, a therapeutic dose should be given for at least 10 days.

Dose adjustments

Renal

Administer with caution and reduce dosage if renal function is markedly impaired; safe dosage may be lower than usually recommended. If dialysis is required for renal failure, the daily dose of cefalexin should not exceed 500 mg.

Dose auto-extracted from UK Summary of Product Characteristics (SPC) via the eMC; US FDA prescribing information (openFDA / DailyMed) — cross-check; US labelling may differ from UK — not yet clinician-verified. Always confirm against the product SmPC and your local formulary before prescribing.

Contraindications

Hypersensitivity to the active substance or to any of the excipients
Known allergy to the cephalosporin group of antibiotics

Side effects

Diarrhoea (most frequent)
Nausea and vomiting (reported rarely)
Dyspepsia and abdominal pain
Hypersensitivity reactions (rash, urticaria, angioedema; rarely erythema multiforme, Stevens-Johnson syndrome, toxic epidermal necrolysis; anaphylaxis)
Transient hepatitis and cholestatic jaundice (reported rarely)

Interactions

Aminoglycosides, other cephalosporins, or furosemide and similar potent diuretics — may increase the risk of nephrotoxicity
Probenecid — inhibits the renal excretion of cefalexin; co-administration is not recommended (US labelling)
Metformin — cefalexin increases plasma metformin concentrations; monitor for hypoglycaemia (US labelling)

Clinical monograph

How it works

It is a beta-lactam that inhibits bacterial cell-wall synthesis by binding penicillin-binding proteins, causing bacterial cell death.

Prescribing in practice

In penicillin allergy, cross-reactivity with cephalosporins is low, but avoid in patients with a history of severe or anaphylactic penicillin reactions.
Cefalexin is renally cleared; reduce the dose in significant renal impairment per current prescribing references.
Broad-spectrum antibacterial use carries a risk of Clostridioides difficile infection, so prescribe in line with local antimicrobial guidance.

Monitoring

Routine monitoring is not usually required; review renal function in impairment and reassess if diarrhoea or signs of superinfection develop.

Counselling the patient

Complete the prescribed course and report any rash, swelling or difficulty breathing.
Report severe, persistent or bloody diarrhoea, which may occur during or after treatment.

Evidence & guidelines

An established option for common community infections; choice should follow local antimicrobial guidance and resistance patterns.

Reference: NICE CKS; NICE NG109; UKHSA; Drug verified in RxNorm (NLM); confirm dosing against the manufacturer SPC (eMC). Verify against your local formulary and current prescribing references before prescribing. The structured dose values shown have been reviewed by a clinician. Monograph status: clinician-reviewed (2026-07-04).

Curated clinical cross-links plus same-class fallbacks.

Calculators

Drugs

Cefadroxil · First-generation oral cephalosporin

Pathways