THE PRESERVATION OF OPHTHALMIC PREPARATIONS 389 DR. E. E. BOEnM: It has recently been pointed out by several authors (64-65) that a phydroxybenzoate concentration of 0.0343 •o, as recommended in the B.P.C. for eye drops preservation is insufficient. It has already been pointed out by Williams et al (65), that the addition of at least 0.08•o of phydroxybenzoates is necessary for the successful inhibition of microbial growth in eye drops. They further pointed out that phydroxybenzoate concentrations of the order as recom- mended by the B.P.C. were ineffective against less resistant micro-organisms and therefore it could hardly be expected that at these low concentrations of the phydroxy- benzoates they would be effective against a much more resistant organism such as Pseudomonas aeruginosa, which is also resistant against benzethonium chloride (67). We have also shown that the addition of 0.00 •o Nipasteril, another phydroxy- benzoate combination, does not only inhibit the growth of an especially resistant strain of Pseudomonas aeruginosa in a buffered aqueous solution, but also killed the organism between 5 and 24 hr. Recently Miiller (68), on the basis of his own experience, recommended the addition of 0.07 •o methyl and 0.03 •o propyl phydroxybenzoates to eye drops, and Montgomery et al (64) the addition of 0.003•o methyl and 0.023•o propyl phydroxybenzoates. DR. BROWN: I think you will find in the paper that we agree that the con- centration recommended in the B.P.C. is not likely to produce sterility with such organisms as Pseudomonas aeruginosa. However, I personally think that this field has been cluttered up with all sorts of opinions and assertions. One can pick almost any chemical and it is possible to find three or four references to workers recommend- ing it. If, however, one critically evaluates the experimental procedures the recommendation often lacks weight. We have to give particular emphasis to those workers who have precisely stated their experimental conditions, have stated how many cells they used, what the medium was, recovery conditions and have correlated the efficiency of their inactivating agents with in vivo tests. Few people have done this. Riegelman et al (1) in the U.S.A. have done this. Their work was followed by I(ohn et al with two excellent papers (24,25). I am unable to comment on your reference to the experience of Mailer because I have not had an opportunity to see this reference. I have seen the reference by Montgomery and Halsall (64), and although they recommend the hydroxybenzoates they give no experimental details about their findings. I am not criticising them for omitting details because their views were merely expressed in a short letter. MR. J. ¾.. JEFFRIES : In your summary you state that at present there is no single ideal preservative for ophthalmic preparations and in particular that strains of Pseudornones aeruginosa or closely related types become resistant to all known preservatives. Referring to the Achromabacter species, there would again appear to be no effective preservative and in any case differentiation between the two types is very difficult. Would you please indicate if, in fact, these organisms are very thermolabile, since I believe their optimum growth temperature is of the order of (64) Montgomery, M. F. and K. G. Halsall, Pharmaceut. J. 192 407 (1964). (65) Sabalitschka, Th., Pharmaz. Zt.•. 108 1723 (1963). (66) Williams, 1•. and Boehm, E. E. Lancet 2 790 (1963). (67) Pivnick, H. et al J. Pharmac. Sc. 52 883 (1963). (68) Miiller, F. Pharrnaz. Praxis 71 (1964).

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