Mupirocin Ointment: Uses, Benefits and Side Effects

Mupirocin ointment is an antibiotic that you apply to the skin. It is prescribed for bacterial skin infections, most often impetigo — a contagious, crusted infection that is common in children. It acts only on bacteria, so it does not help with fungal, viral or allergic skin problems.

Bacterial skin infections often begin at a small break in the skin - a scratch, an insect bite, or a patch of eczema - which lets bacteria get in. The skin around that spot then turns red, becomes weepy, and forms a honey-coloured crust. When the infection is limited to a small area, doctors often prefer an antibiotic that is applied to the spot rather than a tablet that travels through the whole body. Mupirocin ointment is one of the most widely prescribed of these. This article explains what it is used for, how it helps, and the practical points - how long to use it, who needs extra care, and when to call a doctor.

Mupirocin ointment is a topical antibacterial — an antibiotic that you apply to the skin. It contains mupirocin 2% w/w in a non-greasy base made of polyethylene glycol. The mupirocin in it is not made in a laboratory; it is produced by fermenting a type of bacteria called Pseudomonas fluorescens.

Mupirocin comes in three forms, and they are not interchangeable.

• Skin ointment (the form this article covers); Active ingredient: Mupirocin 2% w/w; What you need to know: For bacterial skin infections on the skin

• Skin cream; Active ingredient: Mupirocin 2%, as mupirocin calcium; What you need to know: A separate form — use it only if your doctor prescribed the cream

• Nasal ointment; Active ingredient: Mupirocin 2% w/w, in single-use tubes; What you need to know: For clearing MRSA from the nose in adults, children aged 12 years and over, and healthcare workers

Mupirocin works by blocking a bacterial enzyme called isoleucyl transfer-RNA synthetase. That enzyme is needed by the bacteria to build proteins. Once it is blocked, the bacteria cannot make the proteins they need, so they stop multiplying and the infection clears. Because mupirocin acts on a step that other antibiotics do not use, it does not share resistance with any other antibiotic class.

Mupirocin ointment is used to treat bacterial skin infections. In India, the prescribing information for mupirocin ointment lists these uses:

• Impetigo - a contagious, crusted skin infection usually caused by Staphylococcus aureus or Streptococcus pyogenes.
• Folliculitis - infection of the hair follicles.
• Furunculosis - boils.
• Ecthyma - a deeper skin infection that forms an ulcer with a crust.
• Infected eczema - where patches of eczema have become infected.
• Infected minor wounds - abrasions, insect bites, small cuts, and small burns that do not need hospital care.
• Prevention - to help stop small wounds, incisions and clean lesions from getting infected.

Antibiotic labels differ from country to country. In the United States the skin ointment's approved use is narrower: the FDA first approved it in 1987 for impetigo, and that remains its only approved skin use there. Indian labelling is broader and covers the infections listed above, so follow the pack you were given in India.

What mupirocin ointment is not for

• Fungal infections. It does not work on ringworm, athlete's foot or other fungal skin problems.
• Viral infections. It does not work on cold sores or other viral rashes.
• Eczema itself. It treats an infection sitting on top of eczema, not the eczema.
• The eyes, nose, mouth or vagina. The skin ointment is not made for moist surfaces.

A separate mupirocin nasal ointment exists for that specific purpose (see the table above); it is not recommended for preventing infection in general, and the skin ointment described in this article must never be used inside the nose.

Babies and people with a weakened immune system may need antibiotic tablets as well, or instead, to stop the infection causing more serious problems. Your doctor will decide this.

When a doctor prescribes mupirocin ointment for a bacterial skin infection, these are the practical advantages.

• It treats the infection where it is. You apply it directly to the infected skin, so the antibiotic is concentrated at the spot where the bacteria are.
• Very little of it reaches the rest of the body. Absorption through intact skin is minimal, which is why side effects affecting the whole body are uncommon.
• It covers the bacteria that usually cause impetigo. It is active against Staphylococcus aureus and Streptococcus pyogenes.
• It works against many staphylococci, including methicillin-resistant strains. For MRSA, though, the bacteria should be tested for mupirocin susceptibility before the ointment is relied on.

In the trials that led to its approval for impetigo, 71 in 100 people treated with mupirocin ointment improved, compared with 35 in 100 treated with the same ointment base without the antibiotic. In a second trial, 93 in 100 people using mupirocin ointment improved, compared with about 78 in 100 taking an oral antibiotic. These are results from controlled studies; your own response depends on the infection and on how closely the course is followed.

Use it exactly as your doctor prescribes. The Indian prescribing information advises a small amount applied to the affected area 2 to 3 times a day for up to 10 days. US labelling for the same ointment states 3 times daily.

1. Wash your hands before you start.
2. Wash the affected skin gently and let it dry.
3. Squeeze a small amount onto a cotton swab or a gauze pad and spread a thin layer over the affected area.
4. Cover the area with a clean gauze dressing if you want to, unless your doctor has told you to leave it open.
5. Wash your hands again after applying it.
6. Keep going for as long as your doctor prescribed, usually up to 10 days, and finish the course even if the skin looks better.

If the infection has not begun to improve within 3 to 5 days, contact your doctor. The ointment may not be the right treatment for that infection.

There is no fixed time of day for applying it. Follow the schedule your doctor has given you, and try to keep the doses evenly spaced. Food does not matter for a skin ointment, so there is nothing to plan around meals.

Do not use mupirocin ointment if you are allergic to mupirocin or to any of the other ingredients in the ointment. This is the only situation in which it must be avoided completely.

If you have had a reaction to mupirocin in the past - a rash, itching, swelling or difficulty breathing after using it - do not use it again. Tell your doctor, so a different antibiotic can be chosen.

Most people can use mupirocin ointment safely when it has been prescribed for them, but some situations need extra care.

• Kidney problems and large areas of damaged skin. The ointment base contains polyethylene glycol, which the kidneys remove from the body. Polyethylene glycol can be absorbed through broken or damaged skin, so the ointment should not be used where a large amount could be absorbed — especially if you have moderate or severe kidney disease. Tell your doctor about any kidney problem before you use it.
• The eyes. If any gets in, rinse thoroughly with water.
• Burns. Do not apply it to a burn unless your doctor has told you to.
• Intravenous lines. Do not apply it to skin near an IV cannula or at a central line site.
• Long or repeated use. Prolonged use can let other organisms, including fungi, grow on the treated skin. Use the ointment only for as long as your doctor advised.
• Pregnancy. There is not enough information from human use to be certain that mupirocin ointment is safe in pregnancy. Only a tiny amount is absorbed through intact skin, so doctors do still prescribe it. Tell your doctor if you are pregnant or planning a pregnancy.
• Breastfeeding. It is not known whether mupirocin passes into breast milk. If you are treating the breast or a cracked nipple, wash the area thoroughly before you feed your baby.
• Children. For impetigo, mupirocin ointment has been studied in children from 2 months to 16 years of age. It has not been shown to be safe and effective in babies under 2 months.
• Older adults. No special restriction applies unless there is moderate or severe kidney impairment.
• Driving and machines. Mupirocin ointment has not been found to affect your ability to drive or operate machinery.

Most side effects are mild and limited to the skin where the ointment was applied.

• Common - Burning at the application site
• Uncommon - Itching, redness, stinging or dryness at the application site
• Uncommon - A sensitivity reaction - an allergic rash, redness or soreness in the treated area
• Very rare - Serious allergic reactions: hives, swelling of the face, lips, mouth or tongue, a rash over the whole body, wheezing or trouble breathing, dizziness or a pounding heartbeat
• Frequency not known - A type of diarrhoea called C. difficile-associated diarrhoea, which can range from mild to severe

In clinical trials of mupirocin ointment for impetigo, burning, stinging or pain was reported by about 1.5 in 100 people, and itching by about 1 in 100.

Stop using the ointment and get medical help immediately if you develop swelling of the face, lips, mouth or tongue, wheezing or difficulty breathing, a rash spreading over your body, or dizziness with a fast heartbeat. These are signs of a serious allergic reaction.

Also get medical help quickly if the redness spreads, if the skin becomes very painful, hot or swollen, or if it starts to ooze pus. The same applies if you or your child develops a fever or feels generally unwell. These can be signs that the infection is spreading and that the ointment alone is not enough.

Yes, it can. Bacteria can become resistant to mupirocin, and this is becoming more common. Resistance is seen more often in MRSA than in other staphylococci.

There are two levels of resistance. Low-level resistance comes from changes in the bacteria's own enzyme. High-level resistance is carried on a piece of DNA that can pass from one bacterium to another; when this happens, the ointment will not work against that infection.

Resistance is linked to repeated and long courses of mupirocin and to using it without a clear need. In one study of 140 healthcare workers at an Indian hospital, mupirocin resistance was found in 2 of the 20 MRSA strains and 5 of the 34 strains of a related, harder-to-treat group of skin bacteria called coagulase-negative staphylococci.

To lower the risk:

• Use the ointment only when a doctor has prescribed it for a diagnosed bacterial infection.
• Prolonged, repeated or uncontrolled use of mupirocin is linked to resistance, so do not use it for longer than your doctor advised.
• Do not share your tube with anyone else, even if someone else has a similar-looking rash.

The prescribing information for mupirocin ointment states that no drug interactions have been identified.

• Do not apply other lotions, creams or ointments to the treated area at the same time. Mixing them can dilute the mupirocin and reduce how well it works.
• If you have also been prescribed another skin product for the same area, ask your doctor how to use the two together.
• Alcohol does not interact with mupirocin ointment, because it is applied to the skin and very little is absorbed into the body.
• The nasal mupirocin ointment should not be used at the same time as other products inside the nose.

If you forget a dose, apply it as soon as you remember. If your next dose is almost due, skip the missed one and carry on with your usual schedule. Do not apply a double amount to make up for it.

There is limited experience with mupirocin overdose, and no specific treatment for it, so care is supportive. Wipe off any excess ointment and call your doctor if the skin becomes very irritated.

Because this ointment is meant for the skin, swallowing it is not expected. If a child or anyone else swallows the ointment, take the tube with you and get medical help straight away — call 112 for emergency help, or 108 for an ambulance, or go to the nearest hospital emergency department.

• Keep the tube out of the reach of children.
• Store it protected from direct sunlight at a temperature not exceeding 25°C. Do not freeze it.
• Keep the cap closed and the tube in its carton.
• Wash your hands after you apply it.
• Throw away any ointment left over when your treatment ends. Do not keep it for a future skin problem.

Mupirocin ointment is a prescription-only medicine in India. It cannot be bought without a valid doctor's prescription, and it should be used only for the infection your doctor prescribed it for. This article is general information and does not replace advice from your own doctor. Do not start, stop or change any medicine on your own.