Polymyxin B is an antibiotic that is given as part of treatment of Gram Negative infections caused by susceptible strains of Pseudomonas Aeruginosa, Klebsiella, E. coli, etc. These bacteria give rise to urinary tract infections, meningitis, and bacteremia in patients.
How does Polymyxin B work?
It has bactericidal action against all gram negative bacteria except the Proteus group, while Gram negative cocci and gram positive bacteria are resistant to it. Polymyxin B acts by destabilizing the bacterial cell wall, and making it more permeable. It also dissolves the hydrophobic portion of the cell wall, and blocks the bacterial endotoxin. As a result, the cellular respiration is obstructed, and the bacteria imbibe too much water and die.
Polymyxin B is made up of the sulfate salt of Polymyxin B1 and B2 , both obtained from Bacillus polymyxa.
What is Polymyxin B used to treat?
Polymyxin B is used for treatment of severe infections, through topical to parenteral routes of administration. It is used in ointment form in combination with Neomycin and bacitracin to combat mild infections in superficial wounds, and to accelerate wound healing. It is used subconjunctivally for treatment of eye infections caused by susceptible strains of Psuedomonas aeruginosa, that are generally resistant to other drugs.
Ophthalmic solutions in combination with Trimethoprim are also widely used for corneal and conjunctival infections. Polymyxin B is effective against the gram negative E.coli, which is why it used to treat urinary tract infections caused by coliforms. It is useful against meningeal infections and administered by the intra thecal route or maximum efficacy. Also in cases of bacteremia, it is effective in controlling the spread of infection through the body.
Possible side affects of Polymyxin B
Side effects of Polymyxin B arise due to its nonspecific action against cell walls. The major adverse affects arise from nephrotoxic and neurotoxic features, giving rise to albuminuria, azotemia and retention of drug in the blood stream, dizziness, flushing, parasthesia of the peripheries, and more associated with intrathecal administration- neck stiffness, headache, fever, among others.
Other less commonly reported side effects include fever, and thrmbophlebitis and urticarial rash at the injection site. Contraindications include people who have a history of allergic reaction to Polymyxin B. Patients with reduced renal function need to be monitored carefully as well, and low dosages employed in persons with renal damage. Patients already on curare-like muscle relaxants should not be given Polymyxin B, as the additive effect on respiratory function which may lead to apnea (cessation of breathing).
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