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Pharmacology: Pharmacodynamics: Oxytetracycline is a product of the metabolism of Streptomyces rimosus and is one of the family of tetracycline antibiotics. Oxytetracycline is primarily bacteriostatic and is thought to exert its antimicrobial effect by the inhibition of protein synthesis. Oxytetracycline is a broad-spectrum antibiotic which is useful topically for prevention or treatment of superficial infections due to a variety of pyogenic bacteria, both gram-positive and gram-negative.
The drugs in the tetracycline class have similar antimicrobial spectra, and cross resistance among them is common.
Polymyxin B Sulfate, one of a group of basic polypeptide antibiotics derived from B.polymyxa, is bacteriocidal. It is thought to act by altering the structure of the bacterial membrane resulting in leakage of essential intracellular components. Polymyxin B has antimicrobial activity against a wide variety of gram-negative microorganisms. It is particularly effective against infections caused by Pseudomonas aeruginosa and Haemophilus aegyptius, frequently found in local infections of the eye.
Thus the combination of Oxytetracycline and Polymyxin B sulfate is a particularly effective antimicrobial combination against primarily causative or secondarily infecting organisms.
One mg of pure Polymyxin B is equivalent to 10,000 units.
Pharmacokinetics: Oxytetracycline: In one study in rabbits with abraded corneas, oxytetracycline hydrochloride concentrations of 28 mcg/ml were detected in the aqueous humor 30 minutes after 5-minute bathing of the eye with a solution containing 5 mg/ml.
Polymyxin B: In one study in rabbits, 0.1 mcg/ml concentrations of polymyxin B were detected in the aqueous humor and vitreous humor following six topical applications of 0.25% polymyxin B, one every 10 minutes.
Toxicology: Preclinical safety data: Not applicable.
