biology

Polymyxin B

Polymyxin B is a biology topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Polymyxin B rather than just read about it. In short: Polymyxin B, sold under the brand name Poly-Rx among others, is an antibiotic used to treat meningitis, pneumonia, sepsis, and urinary tract infections. While it is useful for many Gram negative infections, it is not useful for Gram positive infections.

Key takeaways

Polymyxin B belongs to biology; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Polymyxin B to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Polymyxin B from memory before moving on to harder problems.

Reference excerpt

Polymyxin B, sold under the brand name Poly-Rx among others, is an antibiotic used to treat meningitis, pneumonia, sepsis, and urinary tract infections. While it is useful for many Gram negative infections, it is not useful for Gram positive infections. It can be given by injection into a vein, muscle, or cerebrospinal fluid or inhaled. The injectable form is generally only used if other options are not available. It is also available as the combinations bacitracin/‌polymyxin B and neomycin/‌polymyxin B/‌bacitracin for use on the skin. Common side effects when given by injection include kidney problems, neurological problems, fever, itchiness, and rash. Injections into muscle may result in significant pain. Other serious side effects may include fungal infections, anaphylaxis, and muscle weakness. It is unclear if use during pregnancy is safe for the baby. Polymyxin B works by breaking down the cytoplasmic membrane which generally results in bacterial cell death. Polymyxin B was approved for medical use in the United States in 1964. It is on the World Health Organization's List of Essential Medicines. It is available as a generic medication. In the European Union it is only approved to be applied to the skin as of 2015. It is derived from the bacterium Paenibacillus polymyxa (formerly known as Bacillus polymyxa). In 2023, the combination of polymyxin B with dexamethasone and neomycin was the 260th most commonly prescribed medication in the United States, with more than 1 million prescriptions.

Medical uses

Spectrum of susceptibility Polymyxin B has been used to treat urinary tract infections and meningitis caused by Pseudomonas aeruginosa and Haemophilus influenzae, respectively. The following represents MIC susceptibility data for a few medically significant microorganisms.

Haemophilus influenzae: ≥0.8 μg/mL Pseudomonas aeruginosa: 0.25–1 μg/mL

Endotoxin adsorption

An effective use of polymyxin B is found in patients with refractory septic shock, that is, without positive outcome to the administration of standard treatments (increase in volemia and other antibiotics). The obstacle of the toxicity of polymyxin B is bypassed by extracorporeal circulation with perfusion of venous blood through a cartridge on whose fibers polymyxin B is covalently fixed; in this way the antibiotic exerts its bactericidal function but is not released into the blood since it remains fully attached to the fiber. Through this perfusion the cartridge retains the endotoxin, recognized as the trigger of septic shock. The treatment of the cartridge to polymyxin B (Toraymyxin, medical device designed and produced by the Japanese Toray), takes place in two sessions of two hours each, carried out at a distance of 24 hours.

Mechanism of action Alters bacterial outer membrane permeability by binding to a negatively charged site in the lipopolysaccharide layer, which has an electrostatic attraction for the positively charged amino groups in the cyclic peptide portion (this site normally is a binding site for calcium and magnesium counter ions); the result is a destabilized outer membrane Fatty acid portion dissolves in hydrophobic region of cytoplasmic membrane and disrupts membrane integrity Leakage of cellular molecules, inhibition of cellular respiration Binds and inactivates endotoxin Relative absence of selective toxicity: nonspecific for cell membranes of any type, highly toxic. Removal of the hydrophobic tail of polymyxin B yields polymyxin nonapeptide (PMBN), which still binds to LPS, but no longer kills the bacterial cell. However, it still detectably increases the permeability of the bacterial cell wall to other antibiotics, indicating that it still causes some degree of membrane disorganization.

Mixture composition Polymyxin B is composed of polymyxins B1, B1-I, B2, B3, and B6. Polymyxins B1 and B2 are considered major components. These related components are structurally identical with the exception of a variable fatty acid group on each fraction. Results from in vitro studies have shown marginal differences in MIC data when comparing the fractions.

Research application Polymyxin B is also used to induce envelope stress in order to study the organisms' response to such stress. Polymyxin envelope stress assays such as this have been used for the study of small RNA (sRNA) responses in Salmonella enterica.

References

Illustrations

Worked examples

Example 1 — a first encounter with Polymyxin B

Start with the simplest possible case. Write down what Polymyxin B claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In biology, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Polymyxin B before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Polymyxin B ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Polymyxin B

In research: Polymyxin B appears in biology research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Polymyxin B in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Polymyxin B is common in secondary-school and first-year university syllabi. It links to neighbouring topics Cyclic peptides, Otologicals, Over-the-counter drugs in the United States, so understanding it makes those chapters shorter.
In everyday life: Look for Polymyxin B outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Polymyxin B in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Polymyxin B means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Polymyxin B out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Polymyxin B in simple terms?

Why does Polymyxin B matter?

Because it connects several biology ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Polymyxin B?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Polymyxin B.