Neosporin (Neomycin Sulfate / Polymyxin B Sulfate / Bacitracin Zinc Ophthalmic) - Description and Clinical Pharmacology

Description

NEOSPORIN OPHTHALMIC OINTMENT (neomycin and polymyxin B sulfates and bacitracin zinc ophthalmic ointment) is a sterile antimicrobial ointment for ophthalmic use. Each gram contains: neomycin sulfate equivalent to 3.5 mg neomycin base, polymyxin B sulfate equivalent to 10,000 polymyxin B units, bacitracin zinc equivalent to 400 bacitracin units, and white petrolatum, q.s.

Neomycin sulfate is the sulfate salt of neomycin B and C, which are produced by the growth of Streptomyces fradiae Waksman (Fam. Streptomycetaceae). It has a potency equivalent of not less than 600 µg of neomycin standard per mg, calculated on an anhydrous basis. The structural formulae are:

Polymyxin B sulfate is the sulfate salt of polymyxin B₁ and B₂, which are produced by the growth of Bacillus polymyxa (Prazmowski) Migula (Fam. Bacillaceae). It has a potency of not less than 6,000 polymyxin B units per mg, calculated on an anhydrous basis. The structural formulae are:

Bacitracin zinc is the zinc salt of bacitracin, a mixture of related cyclic polypeptides (mainly bacitracin A) produced by the growth of an organism of the licheniformis group of Bacillus subtilis var Tracy. It has a potency of not less than 40 bacitracin units per mg. The structural formula is:

Clinical Pharmacology

A wide range of antibacterial action is provided by the overlapping spectra of neomycin, polymyxin B sulfate, and bacitracin.

Neomycin is bactericidal for many gram-positive and gram-negative organisms. It is an aminoglycoside antibiotic which inhibits protein synthesis by binding with ribosomal RNA and causing misreading of the bacterial genetic code.

Polymyxin B is bactericidal for a variety of gram-negative organisms. It increases the permeability of the bacterial cell membrane by interacting with the phospholipid components of the membrane.

Bacitracin is bactericidal for a variety of gram-positive and gram-negative organisms. It interferes with bacterial cell wall synthesis by inhibition of the regeneration of phospholipid receptors involved in peptidoglycan synthesis.

Microbiology: Neomycin sulfate, polymyxin B sulfate, and bacitracin zinc together are considered active against the following microorganisms: Staphylococcus aureus, streptococci including Streptococcus pneumoniae, Escherichia coli, Haemophilus influenzae, Klebsiella/Enterobacter species, Neisseria species, and Pseudomonas aeruginosa. The product does not provide adequate coverage against Serratia marcescens.