Anti-infective
Cephalosporins
Beta-lactam antibiotics (e.g. cefalexin, ceftriaxone) — A broad family of beta-lactam antibiotics used across many infections, grouped into "generations".
Education and reference only. This is a plain-language class overview — it deliberately contains no doses. Always check the current Summary of Product Characteristics (SmPC), the BNF and your local formulary before prescribing or administering any medicine.
Quick answer
What is Cephalosporins?
Cephalosporins are a broad group of beta-lactam antibiotics, related to penicillins, used to treat a wide range of bacterial infections from simple skin and urinary infections to severe hospital infections. They are organised into "generations" with differing activity.
- How it works: Like penicillins, they kill bacteria by blocking the building of the bacterial cell wall, causing the cell to break apart.
- In practice: In practice cephalosporins are a large, reliable family of antibiotics used for chest, urine, skin and more serious infections, chosen by "generation" according to the likely bacteria — earlier generations for simple skin and urine infections, later ones for resistant or severe hospital infections.
What it is
Cephalosporins are a broad group of beta-lactam antibiotics, related to penicillins, used to treat a wide range of bacterial infections from simple skin and urinary infections to severe hospital infections. They are organised into "generations" with differing activity.
How it works
Like penicillins, they kill bacteria by blocking the building of the bacterial cell wall, causing the cell to break apart. Different generations are designed to reach and resist different bacteria, which is why later generations cover more resistant organisms — and why broad use disturbs the gut's normal bacteria and can trigger C. difficile.
In practice
In practice cephalosporins are a large, reliable family of antibiotics used for chest, urine, skin and more serious infections, chosen by "generation" according to the likely bacteria — earlier generations for simple skin and urine infections, later ones for resistant or severe hospital infections. The everyday practical themes are allergy and stewardship. They are beta-lactams, like penicillins, so a careful penicillin-allergy history is taken: the risk of cross-reaction is low but real, and people with a history of a severe, immediate penicillin reaction (anaphylaxis) usually avoid them. Broad-spectrum cephalosporins are also strongly associated with Clostridioides difficile diarrhoea, so they are reserved where needed rather than used first-line, in line with antibiotic stewardship. As with all antibiotics, the course is completed as advised, and they are ineffective against viral illnesses. Some interact with alcohol or anticoagulation, and most are renally cleared so dosing is adjusted in kidney impairment.
Examples
Practical use
How to take it & use it well
- Take the full course exactly as prescribed, even once you feel better, as stopping early can let the infection return and encourages resistant bacteria.
- Space the doses evenly through the day as directed, so the level in your body stays steady enough to keep fighting the infection.
- Some of these antibiotics are better taken with food to reduce stomach upset, while others can be taken with or without, so follow the advice for the one you have.
- Tell your prescriber before starting if you have ever had a serious allergic reaction to penicillin, as a small number of people react to both groups of antibiotics.
- If you miss a dose, take it as soon as you remember unless it is nearly time for the next one, then carry on as normal. Do not take two doses at once.
- Some forms are given by injection or drip in hospital for more serious infections, while milder ones are treated with capsules or liquid at home.
Common uses
- Skin, urinary and respiratory infections
- Severe or hospital-acquired infections (later generations)
- Surgical prophylaxis and some specific infections
Monitoring
- Clinical response and signs of allergy
- Bowel symptoms suggesting C. difficile
- Renal function (dose adjustment) and, with prolonged use, blood counts
Weighing it up
Advantages & disadvantages
Advantages
- They treat a wide range of bacterial infections, from skin and urine infections to more serious chest and bloodstream infections.
- They are a useful alternative for some people, and stronger forms can be given by drip for severe infections in hospital.
- They are generally well tolerated, with side effects that are usually mild.
- Different members of the group cover different bacteria, so the right one can be matched to the infection.
- Many courses are short and straightforward, fitting easily into a daily routine at home.
Disadvantages
- They can cause diarrhoea, feeling sick and tummy upset, and occasionally a more serious bowel infection after antibiotic use.
- A small number of people who react to penicillin may also react to these, so allergies must be checked first.
- Like all antibiotics, overuse drives resistance, so they are only used when a bacterial infection is likely.
- They can disturb the natural balance of bacteria and yeast, sometimes leading to thrush.
- They do not work against viral illnesses such as colds and most sore throats.
Key safety principles
What to watch for
- Beta-lactam like penicillin — take a careful allergy history; avoid in those with a history of severe immediate penicillin reaction (anaphylaxis).
- Broad-spectrum agents carry a notable risk of Clostridioides difficile diarrhoea — reserve and use per stewardship.
- Ineffective against viruses; complete the course; dose is reduced in kidney impairment.
Key interactions
What to avoid or check alongside
- Antibiotics can reduce how well the body clears the contents of the gut, and broad-spectrum ones can occasionally affect how the contraceptive pill works if you have sickness or diarrhoea.
- Taken with the blood thinner warfarin, some can increase the effect and raise the risk of bleeding, so monitoring may be needed.
- Combined with certain other medicines that can affect the kidneys, the strain on the kidneys may increase.
- Alcohol with one particular member of this group can cause flushing and sickness, so it should be avoided during and shortly after the course.
- Tell your pharmacist about all your medicines, as some can affect how well the antibiotic is absorbed or cleared.
Patient & carer advice
- Tell us about any penicillin or antibiotic allergy before starting
- Report severe or watery/bloody diarrhoea, which can occur during or after treatment
- Finish the course as prescribed and do not save antibiotics for later
Use with
Related clinical calculators
Dose and risk decisions for this class often depend on renal function, weight or bleeding/stroke risk. These tools help:
Answers
Cephalosporins: frequently asked questions
Can I take a cephalosporin if I'm allergic to penicillin?
It depends on how severe your penicillin allergy was. A small number of people react to both groups, so if you have had a serious reaction such as swelling or difficulty breathing, tell your prescriber, who can choose a safer option.
Why do I need to finish the whole course?
Stopping early, even when you feel better, can let the infection come back and helps bacteria become resistant. Completing the full course as prescribed gives the best chance of clearing the infection properly.
I've got diarrhoea on this antibiotic — is that normal?
Mild diarrhoea is a common side effect of antibiotics. However, if it becomes severe, watery or contains blood, or you feel very unwell, stop and get medical advice, as it can occasionally signal a more serious bowel infection.
Will this antibiotic stop my contraceptive pill working?
Most antibiotics do not affect the pill, but if you have vomiting or diarrhoea while taking one, absorption can be reduced. Use extra precautions such as condoms if you are unwell, and check the advice for your specific pill.
Do cephalosporins work for a cold or sore throat?
No, most colds and sore throats are caused by viruses, which antibiotics cannot treat. They are only used when a bacterial infection is likely, which is why your prescriber decides whether they are appropriate.
Authoritative sources
Always verify against the source
This overview is for orientation. For doses, interactions, contra-indications and the full monograph, use:
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Common cephalosporins by active ingredient
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