Question

Why is polymyxin only used on the skin?

a.It has no effect on bacteria that live in the GI tract
b.It is sensitive to degradation by acid, making oral delivery unsuitable
c.It can also damage living human cell membranes, but the drug is safely used on the skin, where the other layers of cells are dead
d.It can disrupt the metabolic pathways found in humans

Answer 1

Polymyxin B is used on the skin as an over-the-counter topical antibiotic ointment because it targets and damages the membranes of gram-negative bacteria, but it can also damage the membranes of human cells when administered systemically.

Step-by-step explanation:

Polymyxins are lipophilic polypeptide antibiotics that target the lipopolysaccharide component of gram-negative bacteria and ultimately disrupt the integrity of their outer and inner membranes. However, these drugs also target and damage the membrane of cells in the kidney and nervous system when administered systemically. Therefore, polymyxin B is used on the skin in over-the-counter topical antibiotic ointments, rather than being taken orally. The poor absorption of polymyxin B from the digestive tract and its sensitivity to degradation by acid also contribute to its use on the skin.