PHYSICAL AND CHEMICAL FACTORS

Synopsis--The chemical and physical factors involved in ophthalmic formulations have been considered briefly. The problems of sterility for ophthalmic preparations have been discussed and the evidence relating to the activity of several preservatives examined. Chlorocresol, chlorbutol, benzalkonium chloride and chlorhexidine were shown to have scientific support for use as ophthalmic preservatives. Ophthalmic preparations should be made so as to preserve them against physical, chemical and biological changes which may make them less effective therapeutically. The pharmacist must formulate such preparations with attention to many factors, most important of which are tonicity, pH, stability, viscosity and sterility. It is proposed briefly to consider the chemical and physical factors involved in ophthalmic formulations and to investigate more fully the problems of sterility and preservation against micro-organisms