PMB

Indications

Polymyxin B is an antibiotic. It is most often used on the eye, ear or skin, usually combined with other antibiotics (such as Neomycin, Bacitracin or Trimethoprim) or a steroid, to treat bacterial infections such as conjunctivitis, outer ear infection and infected cuts, burns or wounds. As an injection, it is used in hospital for serious infections caused by resistant Gram-negative bacteria (such as Pseudomonas, Acinetobacter or Klebsiella) when other antibiotics cannot be used.

How It Works

Polymyxin B attaches to the outer layer (membrane) of certain bacteria, mainly Gram-negative types, and makes holes in it, so the contents leak out and the bacteria die. It does not work against viruses or fungi.

Dosage and Administration

• Eye drops or ointment (combination products): usually 1 to 2 drops, or a small amount of ointment, in the affected eye several times a day, as directed, for the full course.
• Ear drops: usually a few drops in the affected ear 3 to 4 times a day, as directed.
• Skin cream or ointment: apply a thin layer to the clean affected area 1 to 3 times a day.
• Injection: given only in hospital by a doctor or nurse; the dose is worked out from body weight and kidney function and given as prescribed.

Finish the course. If there is no improvement within a few days, see your doctor.

Interactions

With the injection, other medicines that can harm the kidneys or nerves increase the risk of damage, including aminoglycosides (such as Gentamicin or Amikacin), Vancomycin, Colistin and Amphotericin B. Muscle relaxants and some anaesthetics used during surgery can increase the risk of breathing muscle weakness. Eye, ear and skin products have few interactions, but wait at least 5 minutes between different eye drops.

Contraindications

• Allergy to polymyxin B or any ingredient of the product.
• Ear drops when the eardrum is damaged or perforated, unless a doctor advises them.
• Eye drops that also contain a steroid should not be used in viral or fungal eye infections.

Side Effects

Eye, ear and skin products: brief burning, stinging, itching or redness. Injection: kidney damage, nerve effects (numbness or tingling around the mouth or in the limbs, dizziness, weakness), pain at the injection site, fever and rash; rarely, weakness of the breathing muscles.

Get urgent medical help if you have swelling of the face or throat, a spreading rash or difficulty breathing. With the injection, tell staff at once about passing much less urine, severe weakness or trouble breathing. With eye products, see a doctor urgently if pain or vision gets worse.

Pregnancy and Lactation

Eye, ear and skin products are absorbed very little and may be used if a doctor advises. The injection is used in pregnancy only when clearly needed, because it could affect the baby's kidneys and nerves. Topical use is generally compatible with breastfeeding; for the injection, ask your doctor.

Precautions and Warnings

Do not share eye or ear drops. Using these products for a long time can allow resistant bacteria or fungi to grow. Do not wear contact lenses during an eye infection. For the injection, kidney function is checked often, and extra care is needed in kidney disease and myasthenia gravis.

Overdose

Overdose with eye, ear or skin products is unlikely. Too much injection can cause kidney failure, severe muscle weakness and stopping of breathing; treatment is given in hospital.

Therapeutic Class

Polymyxin antibiotic (polypeptide antibiotic).

Storage

Eye, ear and skin products: store below 30°C, away from light, and out of the reach of children; throw away eye or ear drops 4 weeks after opening, or as the leaflet says. Injection vials are kept by the hospital in a refrigerator at 2 to 8°C before mixing.