Drugs

Polymyxin antibiotics

Polymyxin antibiotics

Introduction

Classification

Mechanism of action

Polymyxins have high affinity for phospholipids. They have detergent-like action on the cell membrane & bind to phospholipids on the bacterial cell membrane of gram-negative bacteria causing membrane distortion or pseudopore formation i.e. disrupts cell membrane integrity. It leads to leakage of cellular components (ions, amino acids, etc.) & ultimately cell death.
Sensitive bacteria take up more of the antibiotic. Polymyxins may also inactivate the bacterial endotoxin. They exhibit synergism with many other AMAs by improving their penetration into the bacterial cell.

Antibacterial spectrum

Polymyxins are active against gram-negative bacteria only. They are active against most clinically important gram-negative bacteria except Proteus, Serratia and Neisseria. Thay are rapidly acting concentration-dependent bactericidal agents. Both have very similar range of activity, but colistin is more potent on Pseudomonas, Salmonella and Shigella.

Therapeutic uses

Polymyxins have following uses :

  • Topically : Usually in combination with other antimicrobials for skin infections, burns, otitis externa, conjunctivitis, corneal ulcer-caused by gram-negative bacteria including Pseudomonas.
  • Orally : Gram-negative bacillary (E. coli, Salmonella Shigella) diarrhoeas, especially in infants and children, Pseudomonas superinfection enteritis.

Typical uses are for infections caused by strains of multiple drug-resistant Pseudomonas aeruginosa or carbapenemase-producing Enterobacteriaceae.

Resistance

Resistance to polymyxins has never been a problem. There is no cross resistance with any other AMA. However, alterations in the cell membrane lipid polysaccharides allow many species of Proteus and Serratia to be intrinsically resistant.

Side effects

The use of polymyxins drugs has been limited for a long time, due to the increased risk of nephrotoxicity and neurotoxicity (for example, slurred speech, muscle weakness) when used systemically. However, with the increase in gram-negative resistance, they have seen a resurgence in use and are now commonly used as salvage therapy for patients with multidrug-resistant infections. Careful dosing and monitoring of adverse effects are important to maximize the safety and efficacy of these agents.

  • Applied topically, they are safe-no systemic effect or sensitization occurs. A rash is rare.
  • When given orally, polymyxin B may cause occasional nausea, vomiting, diarrhoea.
  • When injected, polymyxin B may cause high toxicity such as flushing and paresthesias (due to liberation of histamine from mast cells), marked kidney damage, neurological disturbances, neuromuscular blockade.

Contraindications

  • Contraindicated in persons having hypersensitivity to any of drug.

For detailed query or in case of uncertainty, Always consult your doctor or pharmacist.

Click to comment

Leave a Reply

Your email address will not be published. Required fields are marked *

Doctoralerts is dedicated to empower each & every person with the knowledge of medical health (including diseases & their cure with medications etc.) to better manage their own health status & thereby, improvement in health status from a particular smallest place to a country or world level.

Subscribe

Categories

Copyright © 2017 | DoctorAlerts does not provide medical advice, diagnosis or treatment.

To Top