did not employ many strains of Ps. aeruginosa in their experiments. It was observed that lecithin, suspended with the aid of glycerin in nutrient broth, was most effective in inactivating polymyxin B sulfate. The possible mechanism of action is similar to that given under benzalkonium chloride. I t was also noted that nutrient broth containing lecithin solubilized by either Tween 20 or Tween 80 was not as effective as the above-mentioned inactivating medium. This observation was also noted by Riegelman, et al. (17). and Bliss and Worth (23). A possible explanation may be that the effective charge of the lecithin molecule is reduced when it is solubilized by the Tweens. This reduction in the inhibiting action of lecithin by the Tweens was not observed with benzalkonium chloride. The Tweens, by themselves, were capable of reducing the antibacterial action of benzalkonium chloride, while they had no such effect on polymyxin B sulfate. SUMMARY 1. Various in vitro studies were carried out to determine the antibacterial effectiveness of various chemical agents to be used as preservatives in ophthalmic solutions against 13 strains of Ps. aeruginosa. Methods were devised to ( a ) differentiate between the bacteriostatic and bactericidal properties of the chemical preservatives by formulating suitable inactivating media, (b) determine the sterilizing time for each chemical preservative, and (c) determine whether the volume of inoculum taken for sampling in the experiment was adequate.
An in Vivo procedure was employed in evaluating the chemical agents to note whether findings would be in agreement with the final results obtained in the in vitro studies.
Journal of Pharmaceutical Sciences
- The following antibacterial agents used or recommended for use in ophthalmic solutions were thoroughly investigated: chlorobutanol, benzalkonium chloride, thimerosol, combinations of methylparaben and propylparaben, phenylmercuric nitrate, phenylethyl alcohol, and polymyxin B sulfate. Of these, only benzalkonium chloride possessed a sterilizing time against Ps. aeruginosa of less than 1 hour.
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