Polymyxin E, penetration into the eye and therapeutic value in experimental infection due to Ps. pyocyanea.

THE polymyxins are a group of five closely allied antibiotics extracted from the Bacillus polymyxa. In vitro and in the field of general medicine they have been found bactericidal to nearly all Gram-negative bacilli, and the good results obtained in combating Ps. pyocyanea infection of burns by the local application of polymyxin (Jackson and others, 1951) suggested the possibility of using them locally in eye diseases. Early experiences with polymyxins A and D, and later with polymyxin C, showed that they caused damage to the renal convoluted tubules (Stansly and others, 1947; Brownlee and Bushby, 1948) and consequently they were not widely used clinically. Polymyxin B (Brownlee and others, 1949) was found to be almost free from nephrotoxic effect, but it gave rise to neurotoxic signs such as ataxia, and also led to severe irritative reactions at the site of injection. The most recent preparation, polymyxin E, has a toxicity similar to that of polymyxin B, but does not cause irritation at the site of injection. It therefore seemed probable that polymyxin E would be suitable for subconjunctival injection. The general level of antibiotic in the body after this method of administration would be small and thus unlikely to lead to any neurotoxic reaction. Eye infections with Gram-negative bacilli are not common but may be of the greatest severity. Treatment in the past has been unsatisfactory but recently good results have been reported with streptomycin therapy (Bignell, 1951; Sorsby and others, 1952). Bignell collected ten cases infected with Ps. pyocyanea during 1950. In his case notes he emphasizes the severity and rapid spread of the infection; he considers that pyocyanea ulcers can be recognized clinically, showing first as a dead white area in the cornea with central superficial necrosis, and later assuming the form of a white ring with a semitransparent centre. If untreated the whole cornea rapidly becomes disorganized. Sorsby also emphasizes the characteristic clinical appearance of corneal ulceration due to Gram-negative bacilli.