Polymyxin B: Mechanism of Action, Composition, Side Effects, Interactions, Precautions and Uses

It is an antibiotic used to treat bacterial infections.

Polymyxin B (polymyxin sulfate b) is an antibiotic used mainly for resistant Gram-negative infections, such as urinary tract infections, meningitis, blood infections, and eye infections.

Polymyxins bind to the cell membrane and alter its structure, making it more porous. The resulting water absorption leads to cell death. Polymyxins are essential cationic peptides that act as detergents.

Mechanism of action

  • It alters the permeability of the bacterial outer membrane by binding to a negatively charged site in the lipopolysaccharide layer, which has an electrostatic attraction for the amino groups positively charged in the cyclic peptide part.
  • The fatty acid portion dissolves in the cytoplasmic membrane’s hydrophobic region and alters the membrane’s integrity.
  • Leakage of cellular molecules, inhibition of cellular respiration.
  • It binds and inactivates endotoxin.
  • The relative absence of selective toxicity: non-specific for cell membranes of any type, highly toxic.

Composition of the mixture

It is derived from the bacterium Bacillus polymyxa. Polymyxin B is composed of several related compounds. It has a bactericidal action against almost all gram-negative bacilli except the genera Proteus and Neisseria.

Polymyxin B is composed of B1, B1-I, B2, B3, and B6. Polymyxins B1 and B2 are considered significant components. These related components are structurally identical except for one group of variable fatty acids in each fraction.

Side effects

Common side effects of Polymyxin B include:

  • Pain.
  • Redness and swelling at the site of the injection.
  • Itching, burning, redness in the eyes.
  • Temporary blurred vision is used as eye drops.

If you experience severe side effects, contact your doctor, such as:


  • Redness
  • Dizziness.
  • Loss of coordination.
  • Drowsiness.
  • Fever.
  • Headache.
  • Numbness or tingling in the hands or feet.
  • Back pain.
  • Neck stiffness.
  • Instability.
  • Eruptions

According to the condition to be treated, the dose of polymyxin B is determined by a doctor.

It can be injected into a vein, muscle, or cerebrospinal fluid or in the area around the eye (subconjunctival sac). It can also be prepared as eye drops.

Interactions with other medications

Polymyxin B may interact with other drugs that can damage the kidneys or nerves, such as:

  • Cisplatin.
  • Colistin
  • High doses of aspirin.
  • Aminoglycosides such as amikacin , gentamicin or tobramycin .
  • Non-steroidal anti-inflammatory drugs.
  • Ibuprofen.


Tell your doctor about all the medicines you are taking.

During pregnancy, Polymyxin B should be used only when prescribed. It is unknown if this medication passes into breast milk when used in the eye. It is unlikely to harm an infant. Consult your doctor before breastfeeding.


In addition to its antibiotic function, polymyxin B has been used to eliminate endotoxin contamination in reagents.

Polymyxin B is also used to induce stress to study the response of organisms to stress. The polymyxin assays around focus like this have been used to study RNA responses in Salmonella enterica.

Polymyxin B has been used to treat urinary tract infections and meningitis caused by Pseudomonas aeruginosa and Haemophilus influenzae.