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Second-generation cephalosporin Pregnancy: eMC §4.6: animal studies have shown no evidence of impaired fertility or teratogenicity, but since there are no adequate or well-controlled studies in pregnant women, caution should be exercised when prescribing for the pregnant patient. Breast-feeding: small amounts of cefaclor have been detected in breast milk after single 500 mg doses (average levels of about 0.2 micrograms/ml or less up to 5 hours later, trace amounts at one hour); as the effect on nursing infants is not known, caution should be exercised when cefaclor is administered to a nursing woman.

Cefaclor

Brand names: Distaclor

Cefaclor is an oral second-generation cephalosporin antibiotic used for susceptible respiratory, urinary and skin 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: 250 mg
Route: Oral
Frequency: Every eight hours
Max: Total daily dosage should not exceed 4 g per day (doses of 4 g per day have been administered safely to normal subjects for 28 days)
eMC §4.2 (Cefaclor 125 mg/5 ml Granules for Oral Suspension — Distaclor Suspension). The usual adult dosage is 250 mg every eight hours; for more severe infections or those caused by less susceptible organisms, doses may be doubled. ELDERLY: as for adults. BETA-HAEMOLYTIC STREPTOCOCCAL INFECTION: therapy should be continued for at least 10 days. PAEDIATRIC (from the same SPC): the usual recommended daily dosage for children is 20 mg/kg/day in divided doses every eight hours; for bronchitis and pneumonia, 20 mg/kg/day in divided doses administered 3 times daily; for otitis media and pharyngitis the total daily dosage may be divided and administered every 12 hours; in more serious infections, otitis media, sinusitis and infections caused by less susceptible organisms, 40 mg/kg/day in divided doses is recommended, up to a daily maximum of 1 g. Suspension volumes stated in the SPC (Distaclor Suspension 125 mg/5 ml and 250 mg/5 ml): under 1 year (9 kg) 2.5 ml three times daily; 1–5 years (9–18 kg) 5.0 ml three times daily; over 5 years 5.0 ml three times daily. Safety and efficacy have not been established for use in infants aged less than one month. Verify all under-18 dosing against a children's formulary. NEUROTOXICITY (§4.4): reports of neurotoxicity have been identified with cephalosporin treatment — symptoms may include encephalopathy, myoclonus and seizures; elderly patients, patients with severe renal impairment and patients with central nervous system disorders are particularly at risk, and discontinuation should be considered if cefaclor-associated neurotoxicity is suspected. CROSS-SENSITIVITY (§4.4): give cautiously to penicillin-sensitive patients, as cross-hypersensitivity including anaphylaxis among beta-lactam antibiotics is clearly documented. SOURCE NOTE: the eMC §4.5 interactions section was not captured in this bundle — the interactions listed below are from US labelling and should be checked against the UK SPC. The openFDA record fetched is CEFACLOR EXTENDED-RELEASE TABLETS (a different formulation, US labelling): adults aged 16 years and older, 500 mg every 12 hours for 7 days for acute bacterial exacerbations of chronic bronchitis, and 375 mg every 12 hours for pharyngitis/tonsillitis (10 days) and uncomplicated skin and skin structure infections (7 to 10 days); that label states 500 mg twice daily of the extended-release tablet is clinically equivalent to 250 mg three times daily of immediate-release cefaclor capsule, and is NOT equivalent to 500 mg three times daily of other cefaclor formulations.

Paediatric dose

Dose: 20 mg/kg
Route: Oral
Frequency: 20 mg/kg is the TOTAL DAILY dose, given in divided doses every eight hours (i.e. three divided doses per day). For otitis media and pharyngitis the total daily dosage may instead be divided and administered every 12 hours. For bronchitis and pneumonia, 20 mg/kg/day in divided doses administered 3 times daily.
Max: In more serious infections, otitis media, sinusitis and infections caused by less susceptible organisms, 40 mg/kg/day in divided doses is recommended, up to a daily maximum of 1 g
eMC §4.2 (Cefaclor 125 mg/5 ml Granules for Oral Suspension). The figure above is milligrams per kilogram PER DAY, not per dose — do not give 20 mg/kg every eight hours. Safety and efficacy have not been established for use in infants aged less than one month. In the treatment of beta-haemolytic streptococcal infections, therapy should be continued for at least 10 days. Suspension volumes stated in the SPC: under 1 year (9 kg) 2.5 ml three times daily; 1–5 years (9–18 kg) 5.0 ml three times daily; over 5 years 5.0 ml three times daily. Serum sickness-like reactions have been reported more frequently in children than in adults (§4.8). Verify against a children's formulary before prescribing.

Dose adjustments

Renal

eMC §4.2: cefaclor may be administered in the presence of impaired renal function and under such conditions the dosage is usually unchanged. §4.4 adds that because the half-life in anuric patients is 2.3 to 2.8 hours (compared with 0.6–0.9 hours in normal subjects), dosage adjustments for moderate or severe renal impairment are not usually required, but cefaclor should be administered with caution in markedly impaired renal function, with careful clinical observation and laboratory studies. HAEMODIALYSIS: haemodialysis shortens the serum half-life by 25–30%; in patients undergoing regular haemodialysis, a loading dose of 250 mg to 1 g administered prior to dialysis and a therapeutic dose of 250–500 mg every six to eight hours maintained during interdialytic periods is recommended.

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.

Paediatric weight-based calculator

eMC §4.2 (Cefaclor 125 mg/5 ml Granules for Oral Suspension). The figure above is milligrams per kilogram PER DAY, not per dose — do not give 20 mg/kg every eight hours. Safety and efficacy have not been established for use in infants aged less than one month. In the treatment of beta-haemolytic streptococcal infections, therapy should be continued for at least 10 days. Suspension volumes stated in the SPC: under 1 year (9 kg) 2.5 ml three times daily; 1–5 years (9–18 kg) 5.0 ml three times daily; over 5 years 5.0 ml three times daily. Serum sickness-like reactions have been reported more frequently in children than in adults (§4.8). Verify against a children's formulary before prescribing.

Verify in a children's formulary

Contraindications

  • Hypersensitivity to the active substance, to any cephalosporins, or to any of the excipients (eMC §4.3)

Side effects

  • Diarrhoea — the most frequent side effect, rarely severe enough to warrant cessation of therapy; also nausea and vomiting, and colitis including rare instances of pseudomembranous colitis
  • Allergic reactions such as morbilliform eruptions, pruritus and urticaria, usually subsiding on discontinuation; rare reports of erythema multiforme major (Stevens-Johnson syndrome), toxic epidermal necrolysis and anaphylaxis (anaphylaxis may be more common in patients with a history of penicillin allergy)
  • Serum sickness-like reactions (erythema multiforme minor, rashes or other skin manifestations with arthritis/arthralgia, with or without fever) — usually during or following a second or subsequent course, and reported more frequently in children than in adults
  • Haematological: eosinophilia, positive Coombs' tests and rarely thrombocytopenia; transient lymphocytosis, leucopenia and rarely haemolytic anaemia, aplastic anaemia, agranulocytosis and reversible neutropenia
  • Hepatic: transient hepatitis and cholestatic jaundice rarely, slight elevations in AST, ALT or alkaline phosphatase. Renal: reversible interstitial nephritis rarely, slight elevations in blood urea or serum creatinine. CNS: reversible hyperactivity, agitation, nervousness, insomnia, confusion, hypertonia, dizziness, hallucinations and somnolence reported rarely; neurological sequelae including tremor, myoclonia, convulsions and encephalopathy have been reported with cephalosporins, mostly in patients with renal impairment given doses exceeding the recommended dose

Interactions

  • Antacids containing magnesium or aluminium hydroxide — diminish the extent of absorption if taken within 1 hour of administration; H2 blockers do not alter the rate or extent of absorption (US labelling for cefaclor extended-release tablets)
  • Probenecid — inhibits the renal excretion of cefaclor (US labelling)
  • Warfarin — rare reports of increased prothrombin time with or without clinical bleeding in patients receiving cefaclor and warfarin concomitantly (US labelling)
  • The eMC §4.5 interactions section was not captured in this bundle — clinician to review it in the UK SPC

Clinical monograph

How it works

It is bactericidal, binding penicillin-binding proteins to inhibit bacterial cell-wall synthesis and cause cell lysis.

Prescribing in practice

  • Avoid in patients with a history of immediate hypersensitivity to penicillins or cephalosporins, as cross-reactivity can cause serious allergic reactions.
  • A serum-sickness-like reaction with rash and arthralgia is recognised, particularly in children, and should prompt discontinuation.
  • As with other broad-spectrum antibiotics, it can precipitate Clostridioides difficile infection.

Monitoring

Routine laboratory monitoring is not required; review clinical response and watch for hypersensitivity or new diarrhoea.

Counselling the patient

  • Complete the full prescribed course even once you feel better.
  • Stop and seek urgent advice if you develop a rash, joint pains, swelling or breathing difficulty.
  • Report severe or persistent diarrhoea rather than treating it yourself.

Evidence & guidelines

Cefaclor is a long-established oral cephalosporin with efficacy supported by extensive clinical use and the SPC.

Reference: NICE CKS; BSAC; UKHSA AMR; 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).

Related

Curated clinical cross-links plus same-class fallbacks.

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