An antiserum that neutralises diphtheria toxin
Diphtheria antitoxin
An animal-derived antitoxin given in hospital to neutralise the toxin in diphtheria, a serious bacterial infection.
What is Diphtheria antitoxin?
Diphtheria antitoxin is an emergency hospital medicine used to treat diphtheria, a serious infection in which bacteria release a toxin that can damage the heart, nerves and other organs. It works by binding to and neutralising the toxin that is circulating in the blood before it can cause more harm. Because it is made from animal (usually horse) serum, it carries a real risk of serious allergic reactions and of serum sickness, so a test dose is given first and it is used only under close hospital supervision. It is given alongside antibiotics, which kill the bacteria, and works against toxin that has not yet entered the cells, so it is given as early as possible.
Education and reference only. This is a plain-language guide to Diphtheria antitoxin — it deliberately contains no doses. Doses depend on the person, the brand and the reason for treatment, and belong with your prescriber. Always check the BNF, the product labelling (SmPC) and follow medical advice.
What it is
Diphtheria antitoxin is an antiserum, meaning it is made from the blood serum of animals, usually horses, that have been immunised against the diphtheria toxin. It is used to treat diphtheria, a serious bacterial infection in which the bacteria produce a powerful toxin that can damage the heart, nervous system, kidneys and the lining of the throat. It is an emergency treatment given in hospital, usually into a vein or muscle, and is used together with antibiotics. Because it is an animal product injected into a person, it can trigger serious allergic reactions, so it is given with great care under specialist supervision.
How it works
In diphtheria, the bacteria release a toxin into the body that travels in the blood and damages tissues such as the heart and nerves. Diphtheria antitoxin contains antibodies that bind to this circulating toxin and neutralise it, stopping it from attaching to and entering cells where it would cause harm. It can only act on toxin that is still free in the blood, not toxin that has already entered cells, which is why giving it early matters so much. It does not kill the bacteria themselves, so antibiotics are given as well to clear the infection.
Company & origin
Originated / developed by: Specialist supply.
An emergency hospital treatment used in the UK for diphtheria, made from the blood serum of animals (usually horses) that have been immunised against the toxin.
Practical use
How to take Diphtheria antitoxin
General, dose-free guidance — always follow your prescriber's and the leaflet's specific instructions.
- It is given in hospital by a specialist team, usually as an injection into a vein or muscle, not something you take yourself.
- A small test dose is usually given first to check for an allergic reaction before the full treatment.
- It is given as early as diphtheria is suspected, because it can only neutralise toxin still circulating in the blood.
- It is given alongside antibiotics, which are needed to kill the bacteria causing the infection.
- You will be watched closely during and after treatment for any signs of an allergic or delayed reaction.
Weighing it up
Advantages & disadvantages of Diphtheria antitoxin
Advantages
- Neutralises the diphtheria toxin circulating in the blood before it can cause more damage to the heart and nerves.
- Can be life-saving in a serious, potentially fatal infection when given early.
- Works together with antibiotics to tackle both the toxin and the bacteria.
Disadvantages
- Made from animal serum, so it carries a real risk of serious allergic reactions, including anaphylaxis.
- Can cause a delayed reaction called serum sickness, with fever, rash and joint pains days later.
- Only neutralises toxin still in the blood, so it must be given early and does not undo damage already done.
Practical use
Good to know
The most important thing to understand is that diphtheria antitoxin is made from animal serum, so it carries a genuine risk of serious allergic reactions, including life-threatening anaphylaxis, and of a delayed reaction called serum sickness that can cause fever, rash and joint pains days later. Because of this, a small test dose is usually given first to check for an allergic response, and the antitoxin is only ever given in hospital with emergency treatment for allergy close to hand. Timing is crucial: the antitoxin can only neutralise toxin that is still circulating, so it is given as early as diphtheria is suspected rather than waiting for tests to confirm it. It is given together with antibiotics, which kill the bacteria, because the antitoxin alone does not clear the infection. The specialist team weighs the risk of the allergic reaction against the danger of the disease, which can be fatal.
Who should not take it / use with caution
- It is used with great caution in people known to be allergic to horse serum or who have reacted to it before, where the risk has to be weighed against a life-threatening disease.
- It is only given in hospital where emergency treatment for severe allergic reactions is immediately available.
- The decision to use it, including any test dose, is made by a specialist team balancing the risks against the danger of diphtheria.
Monitoring
- Close watching during and after the infusion for allergic reactions, including blood pressure and breathing.
- Watching for delayed serum sickness in the days after treatment.
- Monitoring the heart and nervous system, as the toxin can affect them even after treatment.
Side effects
- Serious allergic reactions, including anaphylaxis, which can happen quickly and need emergency treatment.
- Serum sickness, a delayed reaction days later with fever, rash, itching and joint pains.
- Local reactions such as redness or swelling where the injection is given, and sometimes fever or chills.
Key interactions
- There are few routine medicine interactions, but tell the team about all medicines and any allergies, especially to horses or previous antiserum.
- It is given together with antibiotics, which treat the infection itself.
- It does not replace diphtheria vaccination, which is still needed for longer-term protection.
Available as: A solution given by injection into a vein or muscle in hospital.
Answers
Diphtheria antitoxin: frequently asked questions
What is diphtheria antitoxin used for?
It is an emergency hospital treatment for diphtheria, where it binds to and neutralises the bacterial toxin circulating in the blood before it can damage the heart and nerves.
Why is a test dose given first?
Because the antitoxin is made from animal serum, it can cause serious allergic reactions, so a small test dose is usually given first to check how you react.
Does it kill the bacteria?
No. It only neutralises the toxin; antibiotics are given as well to kill the bacteria and clear the infection.
Why does it have to be given so early?
It can only neutralise toxin that is still circulating in the blood, not toxin that has already entered cells, so giving it early limits the damage.
What is serum sickness?
It is a delayed reaction to the animal serum, appearing days after treatment with fever, rash, itching and joint pains, which the hospital team watches for.
Authoritative sources
- BNF
- NICE CKS
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