Cefadroxil

Cefadroxil is an oral first-generation cephalosporin with a longer half-life than cephalexin, allowing twice-daily or, for some indications, once-daily dosing.

Classification. Beta-lactam, first-generation cephalosporin.

Mechanism. Blocks penicillin-binding proteins and cell wall synthesis.

Spectrum. MSSA, streptococci, and some Escherichia coli, Klebsiella and Proteus mirabilis. Poor activity against enterococci, Haemophilus, anaerobes, MRSA and Pseudomonas.

Pharmacokinetics. Oral bioavailability about 90%, unaffected by food. Half-life about 1.5 hours; over 90% excreted unchanged in urine within 24 hours, giving high urinary levels.

A single 1 g loading dose is used in renal impairment. Maximum 2 g daily in adults in most regimens.

Skin and soft tissue infection. 1 g once daily or 500 mg every 12 hours for 5 to 7 days.

Streptococcal pharyngitis. 1 g once daily or 500 mg every 12 hours for 10 days.

Uncomplicated urinary tract infection. Lower tract: 1 to 2 g daily in 1 or 2 doses for 5 to 7 days when the isolate is susceptible.

Bone and joint step-down. 1 g every 12 hours under specialist direction.

Children. 30 mg/kg/day divided every 12 hours; pharyngitis 30 mg/kg once daily (maximum 1 g); maximum 2 g daily.

Alternatives. Cephalexin, flucloxacillin, amoxicillin clavulanate, clindamycin.

Contraindications. Cephalosporin hypersensitivity. Cefadroxil shares an identical side chain with amoxicillin, so penicillin allergy to amoxicillin raises cross-reaction risk.

Adverse effects. Nausea, diarrhoea, rash, Clostridioides difficile infection. Serious: anaphylaxis, severe cutaneous reactions, interstitial nephritis, haemolytic anaemia, cytopenias, seizures in renal failure.

Interactions. Probenecid raises levels; cholestyramine reduces absorption; warfarin INR rise; aminoglycosides and loop diuretics increase nephrotoxicity; oral typhoid vaccine.

Common prescribing errors. Using it for MRSA or enterococcal infection, not reducing the dose in renal impairment, and using it for pyelonephritis.

Special groups. - Pregnancy and breastfeeding: acceptable. - Older adults: adjust by kidney function. - Kidney impairment: first dose 1 g; then creatinine clearance 25 to 50 mL/min 500 mg every 12 hours; 10 to 25 mL/min 500 mg every 24 hours; under 10 mL/min 500 mg every 36 hours. - Liver impairment: no adjustment. - Region: availability in East Africa varies; cephalexin is more common.

Administration. Capsules, tablets or suspension; may be taken with food to reduce nausea.

Baseline and monitoring. - Baseline: allergy history, creatinine if risk of kidney disease. - During treatment: review at 48 to 72 hours; creatinine and full blood count in courses over 14 days. - No therapeutic drug monitoring.

Stop rules. Stop for urticaria, angioedema, mucosal skin reaction or persistent diarrhoea.

Referral and escalation. Refer for spreading cellulitis, systemic features, abscess and failure at 48 to 72 hours.