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Polymyxin B and Trimethoprim Ophthalmic (Polymyxin B Sulfate / Trimethoprim Sulfate Ophthalmic) - Description and Clinical Pharmacology

 
 



Polymyxin B Sulfate and
Trimethoprim Ophthalmic Solution, USP
Sterile

DESCRIPTION

Polymyxin B Sulfate and Trimethoprim Ophthalmic Solution is a sterile antimicrobial solution for topical ophthalmic use. It has a pH of 4.0 to 6.2 and osmolality of 270 to 310 mOsm/kg.

Chemical Names: Trimethoprim sulfate, 2,4-diamino-5-(3,4,5-trimethoxybenzyl)pyrimidine sulfate (2:1), is a white, odorless, crystalline powder with a molecular weight of 678.72 and the following structural formula:

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 formula are:

Contains: Actives: polymyxin B sulfate 10,000 units/mL; trimethoprim sulfate equivalent to trimethoprim 1mg/mL. Preservative: benzalkonium chloride 0.04 mg/mL. Inactives: sodium chloride; sulfuric acid and purified water. May also contain sodium hydroxide for pH adjustment.

CLINICAL PHARMACOLOGY

Trimethoprim is a synthetic antibacterial drug active against a wide variety of aerobic gram-positive and gram-negative ophthalmic pathogens. Trimethoprim blocks the production of tetrahydrofolic acid from dihydrofolic acid by binding to and reversibly inhibiting the enzyme dihydrofolate reductase. This binding is very much stronger for the bacterial enzyme than for the corresponding mammalian enzyme and therefore selectively interferes with bacterial biosynthesis of nucleic acids and proteins.

Polymyxin B, a cyclic lipopeptide antibiotic, is rapidly bactericidal for a variety of gram-negative organisms, especially Pseudomonas aeruginosa. It increases the permeability of the bacterial cell membrane by interacting with the phospholipid components of the membrane.

Blood samples were obtained from 11 human volunteers at 20 minutes, 1 hour and 3 hours following instillation in the eye of 2 drops of ophthalmic solution containing 1 mg trimethoprim and 10,000 units polymyxin B per mL. Peak serum concentrations were approximately 0.03 mcg/mL trimethoprim and 1 unit/mL polymyxin B.

Microbiology: In vitro studies have demonstrated that the anti-infective components of Polymyxin B Sulfate and Trimethoprim Ophthalmic Solution are active against the following bacterial pathogens that are capable of causing external infections of the eye:

Trimethoprim: Staphylococcus aureus and Staphylococcus epidermidis, Streptococcus pyogenes, Streptococcus faecalis, Streptococcus pneumoniae, Haemophilus influenzae, Haemophilus aegyptius, Escherichia coli, Klebsiella pneumoniae, Proteus mirabilis (indole-negative) , Proteus vulgaris (indolepositive), Enterobacter aerogenes, and Serratia marcescens.

Polymyxin B: Pseudomonas aeruginosa, Escherichia coli, Klebsiella pneumoniae, Enterobacter aerogenes and Haemophilus influenzae.

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