Cephalosporins and other Beta Lactams

The cephalosporins are broad spectrum antibiotics. Their pharmacology is similar to penicillins and they are mainly excreted by the kidney. They do not cross the blood brain barrier well, except when the meninges are inflamed. They are derived from fungus and work by inhibiting cell wall synthesis.¹

Where possible treatment should be guided by sensitivities from a cultured specimen. Where empiric treatment is necessary consult your local antibiotic policy - based on the HPA guidance adapted to take account of locally prevalent pathogens and resistance.⁴ Gram negative bacteria resistance to cephalosporins is increasing.⁵

Gastro-intestinal tract

• Typhoid: cefotaxime
• Biliary tract infection: cephalosporin
• Peritonitis: cephalosporin with metronidazole
• Peritoneal dialysis associated peritonitis: cephalosporin with metronidazole

Respiratory tract

• Throat infection: oral cephalosporin (benzyl penicillin is first-line)
• Haemophilus influenzae epiglottitis: cefotaxime
• Severe community acquired pneumonia of unknown aetiology: cefuroxime or cefotaxime with erythromycin
• Hospital acquired pneumonia: broad spectrum cephalosporin
• Acute exacerbation of chronic bronchitis (AECB): second or third generation cephalosporins are more effective, but not less safe than amoxicillin⁶

Central nervous system

• Meningococcal meningitis: cefotaxime
• Pneumococcal meningitis: cefotaxime
• H. influenzae meningitis: cefotaxime

However, a recent Cochrane review shows no clinically important difference between cefotaxime and conventional antibiotics. In situations where availability or affordability is an issue, third generation cephalosporins or an amoxicillin-chloramphenicol combination may be used.⁷

Pelvis

• Pyelonephritis: cephalosporin for 14 days - low UTI 3 days only
• Gonorrhoea: cefotaxime

NB: Treatment with oral antibiotics is as effective as parenteral then oral treatment in the management of the first episode of clinical pyelonephritis in children.⁸

Blood-borne

• Community acquired septicaemia: broad spectrum cephalosporin
• Hospital acquired septicaemia: beropenem or imipenem
• Meningococcal septicaemia: cefotaxime.

They are also commonly used for antibacterial prophylaxis in surgery.

• Stomach/oesophagus/gallbladder: IV cefuroxime, single dose
• Colon or rectum: IV cefuroxime with metronidazole, single dose
• Pelvis: IV cefuroxime with metronidazole, single dose

• Known hypersensitivity to penicillin or cephalosporins. The cross-reactivity with penicillins varies according to which type of cephalosporin is prescribed. It is greatest with first and second generation cephalosporins, (30%), or with cephalosporins containing an amino-benzyl ring (27%). It may be as low as 4-5% with a 3rd generation/no benzyl ring cephalosporin. Patients who recall a definite history of an immediate type of penicillin allergy are more likely to develop a cephalosporin reaction compared with patients who report a delayed, a probable or an unknown penicillin reaction.⁹
• Diabetics should be informed they may have a false positive test for glucose on urine testing, whilst taking cephalosporins.
• They are excreted renally, so patients with renal impairment may have higher circulating concentrations and be more prone to adverse effects. They may require a lower dose.
• It should be used with caution where the patient also has porphyria.

• Hypersensitivity reactions may be seen.
• Diarrhoea and, rarely, antibiotic associated colitis are found. This occurs more commonly with very high doses.
• Interacting with other medications:
  • Combined oral contraceptive pill efficacy is reduced.
    Extra precautions should be used for the duration of the course and 7 subsequent days. If those 7 days run beyond the end of a packet, then the pill free interval should be omitted.
  • Diuretics increase plasma concentrations of cephalosporins and their toxicity.
  • Warfarins anticoagulant effect is enhanced by cephalosporins.
  • Antacids reduce the absorption of cefaclor.
• Cefamandole gives a disulfiram reaction with alcohol.