Treatment of Superficial Ocular Infection with a Polymyxin-bacitracin Ointment

SUPERFICIAL ocular infections, for example blepharitis, are better treated by local applications than by systemic therapy. Local applications of antibiotic and chemotherapeutic agents are also of value in reducing the incidence of infection after corneal injury. Sulphacetamide is most commonly used but, although its value in the prevention of corneal infection is well established (Cameron, 1949), it is active only against a limited range of organisms. Ps. pyocyaneus in particular tends to be resistant to sulphacetamide. Penicillin too is of limited value, being effective only against Gram-positive and coccal organisms, and liable to induce allergic responses. Chloromycetin, aureomycin, and terramycin fail to provide full cover against Ps. pyocyaneus. K In the treatment of infection the ideal procedure is to discover the causative organism by bacteriological examination, so that the most suitable antibiotic may be chosen. This ideal is, however, seldom possible in practice outside hospital, and a topical application active against a large range of organisms and likely to be effective when used empirically is desirable. Indeed, in all cases treatment will have to be started without bacteriological confirmation of the type of infection as it is not justifiable to delay while awaiting the result of culture. Further, the wider the range of antibacterial activity, the greater the value as a prophylactic against wound infection. The perfect antibiotic preparation would be lethal to all ocular pathogens, and sensitive organisms would not be able to develop resistance. In addition a topical application must be non-irritant when applied to the eye and must not give rise to allergic reactions. It is not yet possible to fulfill all these conditions, but the antibiotics bacitracin and polymyxin used together satisfy most of them. Bacitracin and polymyxin are both polypeptides and are extracted from products of growth of the B. licheniformis and B. polymyxa respectively (Finland and Wright, 1953). Bacitracin is effective against Gram-positive organisms and the Gram-negative cocci and has therefore a range very similar to that of penicillin. Polymyxin is active against the Gram-negative bacilli including the Ps. pyocyaneus. As there is no antagonistic action between the two antibiotics, they together cover the whole range of pyogenic organisms commonly causing eye infection. Both bacitracin and polymyxin are suitable for topical application but have disadvantages when given systemically. Bacitracin is highly nephrotoxic (Finland and Wright, 1953), and save in exceptional circumstances