An antibiotic used mainly in ear and eye drops
Polymyxin B
An antibiotic used mainly in ear and eye drops and topical combinations, and rarely by injection for resistant infections.
What is Polymyxin B?
Polymyxin B is an older antibiotic that is used mainly on the surface of the body — in ear drops, eye drops and skin preparations, often combined with other antibiotics or a steroid. Used in this topical way it is generally safe and well tolerated. Its serious risks appear only when it is given into the body by injection, which can affect the kidneys and the nerves; for this reason injectable use is reserved for serious, resistant infections and is supervised by specialists. Most people will only ever meet it as drops or a cream.
Education and reference only. This is a plain-language guide to Polymyxin B — 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
Polymyxin B is a long-established antibiotic that works against certain bacteria. In everyday practice it is used almost entirely on the surface of the body: in ear drops for ear infections, in eye drops for eye infections, and in creams or ointments for the skin, frequently in combination with another antibiotic or with a steroid to reduce inflammation. It can also be given by injection, but only rarely, in hospital, for serious infections caused by bacteria that resist other antibiotics. In that injectable form it needs careful specialist handling because of its effects on the body.
How it works
Polymyxin B attacks the outer covering of certain bacteria, breaking down their surface so the bacteria leak and die. This makes it useful against some hard-to-treat bugs. When it is used as drops or a cream, it acts on the bacteria at the site — in the ear, eye or on the skin — with very little getting into the rest of the body, which is why topical use is generally safe. When it is given by injection, it spreads through the body, where the same powerful action can also affect the kidneys and the nerves, which is why systemic use is limited and closely monitored.
Company & origin
Originated / developed by: Various manufacturers.
An older antibiotic used mainly in ear and eye drops and skin combinations, and rarely by injection for resistant infections.
Practical use
How to take Polymyxin B
General, dose-free guidance — always follow your prescriber's and the leaflet's specific instructions.
- For ear or eye drops, use them exactly as directed and complete the course you are given.
- Apply skin preparations thinly to the affected area as directed, and avoid using them for longer than advised.
- Avoid touching the dropper or tube tip to the eye, ear or skin to keep it clean.
- Stop and seek advice if you develop increasing irritation, a rash or swelling where it is applied, as this may be an allergic reaction.
- The injection is given only in hospital by specialists, with close monitoring of the kidneys and nerves.
Weighing it up
Advantages & disadvantages of Polymyxin B
Advantages
- An effective antibiotic for ear, eye and skin infections when used as drops or a cream.
- Generally safe and well tolerated in its topical forms.
- By injection, offers a reserve option against serious infections caused by resistant bacteria.
Disadvantages
- When given by injection, it can be toxic to the kidneys and the nerves.
- Injectable use is reserved for serious resistant infections and needs specialist supervision.
- Topical use can cause local irritation or allergic skin reactions in some people.
Practical use
Good to know
The key thing to understand is the big difference between how polymyxin B is used. As drops or a cream it is generally safe and well tolerated, with side effects usually limited to local irritation, stinging or, sometimes, an allergic skin reaction. As an injection, however, it can be toxic to the kidneys and to the nerves, which is why it is kept in reserve for serious infections caused by resistant bacteria and is used only under specialist care with close monitoring. For drops, complete the course you are given and do not use them for longer than directed. If you develop increasing irritation, a rash or swelling where it is applied, stop and seek advice, as this may be an allergic reaction.
Who should not take it / use with caution
- People who have had a serious allergic reaction to polymyxin B should not use it.
- Ear drops are used with caution if the eardrum is perforated, on specialist advice.
- The injectable form is used with great caution in people with kidney problems, because of the risk of kidney toxicity.
- Injectable use is reserved for specialist settings where the kidneys and nerves can be closely monitored.
Monitoring
- For injectable use, close monitoring of kidney function during treatment.
- For injectable use, watching for nerve effects such as numbness, tingling or breathing problems.
- For drops and creams, reviewing whether the infection is responding and watching for allergic reactions.
Side effects
- With drops or creams, local stinging, irritation or redness where it is applied.
- Allergic skin reactions, such as a rash or swelling, in some people.
- With injection, effects on the kidneys, such as reduced kidney function.
- With injection, effects on the nerves, such as numbness, tingling or, rarely, breathing problems, which need urgent attention.
Key interactions
- When injected, it can add to the kidney or nerve effects of other medicines, such as certain other antibiotics.
- It may add to the effects of medicines that relax muscles during anaesthesia, relevant to injectable use.
- Topical use has few important interactions, but tell your prescriber about all your medicines.
Available as: Ear drops, eye drops, and skin creams or ointments (often in combination), and a solution for injection used by specialists.
Answers
Polymyxin B: frequently asked questions
What is polymyxin B used for?
It is an antibiotic used mainly in ear drops, eye drops and skin preparations, often combined with other ingredients, and rarely by injection for serious infections caused by resistant bacteria.
Is it safe?
Used as drops or a cream it is generally safe and well tolerated. Its serious risks — to the kidneys and nerves — appear only when it is given by injection, which is reserved for specialist use.
Why is the injection only used rarely?
Given into the body, polymyxin B can be toxic to the kidneys and the nerves, so the injection is kept in reserve for serious resistant infections and is closely monitored by specialists.
Why does my ear or eye sting after the drops?
Local stinging or irritation where the drops are applied is a common, usually mild effect. If you develop increasing irritation, a rash or swelling, stop and seek advice.
Should I finish the course of drops?
Yes, complete the course you are given even if symptoms improve, and do not use the drops for longer than directed.
Authoritative sources
- BNF
- NICE CKS
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