390 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS 25øC whilst at 37 ø they can be killed off, certainly in the presence of preservatives such as the esters of phydroxybenzoic acid at normal concentration after not more than two days' incubation. This might possibly be a method of getting out of difficulty if one had a batch of material that was subsequently shown to be con- taminated heavily with A chromobacter, although it would of course suffer from the serious drawback that the products of metabolism would still be present in the finished product. DR. BRowN: I would just like to make one slight correction. In our paper we did not state that strains of Pseudomonas aeruginosa become resistant to all known preservatives. People from several quarters have been saying that compound X is the thing. Exaggerated claims have been made for chlorhexidine. What we state above (p. 015) is rather different from claiming that Pseudomonas can become resistant to all known preservatives. The point we are making here is that we should be cautious in accepting any new chemical that is heralded as a new wonder preservative. I do not believe there are any. I am puzzled about your second point. In page 003 of our paper we mention Pseudomonas, we mention Aerobacter subtilis and Clostridium. We do not, in fact, mention Achromobacter. Do you in fact mean A chrornobacter ? MR. J. E. J•FFR•S : Yes, I do mean Achromobacter. Surely this is a fairly common contaminant of water used in the production area and it is in fact extremely difficult to get rid of once you have it there. It appears particularly on columns from demineralized water. DR. BRowN: I must confess I am not an expert in this field and as far as I know A chromobacter is not pathogenic, and is not particularly thermolabile. I looked it up in Bergley and the original type species is reported at 20 ø to 25 ø optimum growth. Unfortunately this was a very early work and certain im- portant tests that now seem to be necessary were not carried out. There are many other species listed where the optimum growth temperature is more normal. As far as the heat resistance is concerned, I do not think it is particularly heat labile. You may have come across some odd strains that are, but I certainly have not. DR. O. D. PR•DD•,•: What, in your opinion, is a good preservative for fluorescein sodium solutions ? Fluorescein, as a high molecular weight anion, should react with a cation such as benzalkonium and the phenylmercurate ion. DR. BRow•: Mr. Norton and I agree that the ideal would be a sterile single dose unit for fluorescein sodium, which is mainly used as a diagnostic agent. I would also like to make the point that although I have in fact worked at one eye hospital I am informed that because fluorescein is used frequently in eye hospitals, it is quite common to have a bottle of fluorescein used for months and I suspect that because of this there have been so many reports of fluorescein contaminated by Pseudornonas. I suspect that if it were customary for cups of tea to be left around for months there would be numerous reports of tea being a marvellous medium for Pseudomonas. I think that the problem could be eliminated in this particular case where it has a specific use as a diagnostic agent by using sterile, single unit drops. The Australian formulary which has just been published, uses 0.004•o P.M.N. with fluorescein, and the B.P.C. of course used 0.002•o P.M.N. It would appear

THE PRESERVATION OF OPHTHALMIC PREPARATIONS 391 that they should react. I am not sure that anybody has shown whether in fact it does happen at this concentration. DR. O. D. PmDDLE : Can you make any comments on the physical stability of comparatively low molecular weight preservatives such as chlorobutanol or phenyl- ethanol in solutions contained in polyethylene or other plastic bottles ? DR. BROWN: It seems very likely that there is absorption of some sort between plastics and phenols and as far as we know, not that we know very much, very little is published on this. I think it is very important and we, at Bristol, are certainly coming to the conclusion that we should be progressing towards mass produced, small volume eye drop preparations, rather than extemporaneous preparations as the norm. Information about the effect of these low molecular weight preservatives in the presence of plastics would be useful. MR. M. J. GRovEs: We were interested to note that you refer to Bronopol under the heading of agents not widely used as preservatives, the inference being that it could possibly be considered as a preservative for eye drops. We are also interested in this but we would like to sound a note of warning since Bronopol is not stable at an alkaline pH. We have examined the eye drops officially formulated in the British Pharmaceutical Codex. A number of these are alkaloidal solutions and hence acidic in reaction. But of the g0 eye drops in the Codex, 10 would appear to be either directly incompatible with Bronopol or contraindicated because of the pH. The use of Bronopol as a preservative is therefore somewhat limited and in addition it would be necessary to establish beyond reasonable doubt, that this new antibacterial, and I emphasize the word new or untried, is completely safe to use in the eye. Some work in our own laboratories which has been undertaken on the effect of Bronopol in rabbit eyes had given encouraging results so far, but there is limited information at present on the effects on human eye. We can only reiterate Dr. Harold Davis' comment at the recent British Pharmaceutical Conference, to the effect that reliable information about safety must be obtained under the conditions in which the materials can be used. DR. BRowN: I agree and I would like to point out that Bronopol is mentioned under the heading of agents not widely used as preservatives. In the summary and conclusions we have not made any reference to it at all. We have ignored it, because more work will clearly have to be done on it, as you have suggested. M•ss B. CROSHAW: There is a further word of caution'I would like to add regarding Bronopol. Although we have shown that it is bacteriostatic against both gram- negative and gram-positive bacteria at similar concentrations, the bactericidal activity is much greater against gram-negative organisms than against gram-positive. For this reason we would not recommend the use of Bronopol alone as a satisfactory pre- servative for ophthalmic solutions. Although you do not like combinations, we would only consider it in combination with benzalkonium chloride or something similar. I do not think we should be arguing whether A chromobacter is or is not pathogenic to eyes. I think any organism in an eye drop must be regarded as a potential pathogen, and a preservative that does not deal with it can not really be considered as satisfactory. Concerning the use of chlorhexidine and its breakdown on heating: Are the breakdown products bacteriologically active?