First-Generation Cephalosporin Antibiotic Pregnancy: eMC §4.6: 'Although laboratory and clinical studies have shown no evidence of teratogenicity, caution should be exercised when prescribing for the pregnant patient.' Breastfeeding: excretion in human breast milk increased up to 4 hours after a 500 mg dose, reaching a maximum of 4 micrograms/ml and disappearing 8 hours after administration; caution should be exercised in a nursing woman because of the risk of candidiasis and CNS toxicity in the neonate due to immaturity of the blood-brain barrier, with a theoretical possibility of later sensitisation. The US label states that available epidemiological data and pharmacovigilance reports have not established drug-associated risks of major birth defects, miscarriage or adverse maternal or fetal outcomes.

Cefalexin (Cephalexin)

Brand names: Ceporex, Keflex

Cefalexin is a first-generation oral cephalosporin antibiotic; in this urological context it is used for urinary tract infection and as antibacterial prophylaxis in recurrent UTI. It provides reliable cover against common urinary pathogens.

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: Mild, uncomplicated urinary tract infections: 250 mg every 6 hours, or 500 mg every 12 hours. General adult range: 1-4 g daily in divided doses, with most infections responding to 500 mg every 8 hours

Route: Oral

Frequency: Every 6 hours, every 8 hours or every 12 hours depending on indication and severity

Max: 'If daily doses of cefalexin greater than 4g are required, parenteral cephalosporins, in appropriate doses, should be considered' (§4.2). §4.4: 'If dialysis is required for renal failure, the daily dose of cefalexin should not exceed 500mg.'

SOURCE: eMC UK SPC 'Cefalexin 125mg/5ml Oral Suspension' §4.2, quoted verbatim: 'The adult dosage ranges from 1-4 g daily in divided doses; most infections will respond to a dosage of 500 mg every 8 hours. 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.' The 250 mg q6h / 500 mg q12h regimen is the one that matches this page's urinary indication. SEVERITY: 'For more severe infections, or those caused by less susceptible organisms larger doses may be needed.' ELDERLY AND RENAL IMPAIRMENT: 'As for adults. Reduce dosage if renal function is markedly impaired.' DURATION: in the treatment of beta-haemolytic streptococcal infections a therapeutic dose should be administered for at least 10 days; the US label gives a general duration of 7 to 14 days depending on infection type and severity. FORMULATION NOTE: the fetched SPC is the 125 mg/5 mL oral suspension, but it carries the full adult posology quoted above; capsule/tablet SPCs should be cross-checked if the page presents solid dose forms. US CROSS-CHECK: adults and patients at least 15 years of age — 250 mg every 6 hours, or 500 mg every 12 hours; for more severe infections up to 4 grams daily in two to four equally divided doses. §4.4 of the SPC was truncated at the source-fetch limit.

Paediatric dose

Route: Oral

Frequency: Daily dose in divided doses — usually every 8 hours; for skin and soft tissue infections, streptococcal pharyngitis and mild, uncomplicated urinary tract infections the total daily dose may be divided and administered every 12 hours

eMC §4.2: 'The usual recommended daily dosage for children is 25-50 mg/kg (10-20mg/lb) in divided doses.' dosePerKg is left null because the SPC states a RANGE (25-50 mg/kg/day) and different figures apply by indication. 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.' OTITIS MEDIA: 'clinical studies have shown that a dosage of 75-100 mg/kg/day in 4 divided doses is required.' Beta-haemolytic streptococcal infections: treat for at least 10 days. US CROSS-CHECK (paediatric patients over 1 year): 25 to 50 mg/kg total daily dose in equally divided doses for 7 to 14 days; severe infections 50 to 100 mg/kg/day in equally divided doses; otitis media 75 to 100 mg/kg/day in equally divided doses. No paediatric maximum dose is stated in the fetched SPC. Verify all under-18 dosing against a children's formulary.

Dose adjustments

Renal

eMC §4.2/§4.4: 'Reduce dosage if renal function is markedly impaired'; cefalexin should be administered with caution in markedly impaired renal function, safe dosage may be lower than usually recommended, and 'If dialysis is required for renal failure, the daily dose of cefalexin should not exceed 500mg.' US CROSS-CHECK table (adults and patients at least 15 years): CrCl > 60 mL/min — no dose adjustment; CrCl 30 to 59 mL/min — no dose adjustment but maximum daily dose should not exceed 1 g; CrCl 15 to 29 mL/min — 250 mg every 8 hours or every 12 hours; CrCl 5 to 14 mL/min not yet on dialysis — 250 mg every 24 hours; CrCl 1 to 4 mL/min not yet on dialysis — 250 mg every 48 hours or every 60 hours; insufficient information to make recommendations for patients on haemodialysis.

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 — the most frequent side-effect, very rarely severe enough to warrant cessation; nausea and vomiting reported rarely; dyspepsia and abdominal pain; pseudomembranous colitis may appear during or after treatment
Hypersensitivity — rash, urticaria, angioedema and, rarely, erythema multiforme, Stevens-Johnson syndrome and toxic epidermal necrolysis; anaphylaxis has also been reported; acute generalised exanthematous pustulosis (frequency not known)
Haematological — eosinophilia, neutropenia, thrombocytopenia and haemolytic anaemia
Hepatic and renal — transient hepatitis and cholestatic jaundice reported rarely, slight elevations of AST and ALT; reversible interstitial nephritis reported rarely
Other — genital and anal pruritus, genital candidiasis, vaginitis and vaginal discharge, dizziness, fatigue, headache, agitation, confusion, hallucinations, arthralgia, arthritis and joint disorder; neurological sequelae including tremor, myoclonia, convulsions and encephalopathy have been reported with cephalosporins, mostly in renal impairment at above-recommended doses and resolving on discontinuation

Interactions

Aminoglycosides, other cephalosporins, or furosemide (frusemide) and similar potent diuretics — concurrent administration may increase the risk of nephrotoxicity (SPC §4.4; no separate §4.5 was captured in this bundle)
Metformin (US label §7.1) — administration with cephalexin increases plasma metformin concentrations and decreases metformin renal clearance; careful monitoring and metformin dose adjustment are recommended
Probenecid (US label §7.2) — inhibits the renal excretion of cephalexin; co-administration is not recommended
Laboratory interference — cephalexin may cause a false-positive reaction when testing for glucose in the urine using Benedict's or Fehling's solution; positive direct Coombs' tests have been reported with cephalosporin antibiotics
NOTE: the SPC interaction section was not captured separately in this bundle and §4.4 was truncated — clinician to review the full SPC interaction text

Clinical monograph

How it works

It is a beta-lactam that inhibits bacterial cell-wall synthesis by binding penicillin-binding proteins, leading to cell lysis.

Prescribing in practice

Avoid in patients with a history of immediate or severe hypersensitivity to penicillins or cephalosporins because of cross-reactivity risk.
Dose adjustment is required in renal impairment as the drug is largely renally excreted; follow the SPC.
It is unreliable against Pseudomonas and many resistant Gram-negative organisms, so culture and sensitivities should guide prolonged use.

Monitoring

Routine monitoring is not needed for short courses, but renal function and clinical or microbiological response should be reviewed when used for prophylaxis or in impairment.

Counselling the patient

Complete the prescribed course even if symptoms settle.
Report rash, swelling, or difficulty breathing as these may signal allergy.
Diarrhoea is common; seek advice if it is severe or persistent.

Evidence & guidelines

A long-established cephalosporin with extensive clinical use supporting its efficacy in urinary tract infection and UTI prophylaxis.

Reference: NICE NG109 (UTI in adults); NICE NG113 (UTI in under 16s); PHE Antimicrobial Guidelines; 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

Pathways