Emulsions microbial spoilage

Fig. 18.1 Section (xl. 5) tinough an inadequately preserved olive oil, oil-in-water, emulsion in an advanced state of microbial spoilage showing ... 

Aqueous products that are at greatest risk from microbial spoilage include solutions, suspensions, and emulsions for repeated oral, parenteral, or external use and include critical products such as multidose injections and eye drops. Unpreserved products without adequate antimicrobial efficacy should not be presented in containers intended for use on more than one occasion unless justified. When antimicrobial preservatives are used, their efficacy has to be demonstrated using the Ph Eur test for antimicrobial preservative efficacy. Factors to be taken into account in designing a preserved product include the nature of the preservative, its concentration in the product, the... 

Oral liquid and semisolid formulations containing water as part of the vehicle may be prone to microbial spoilage in the absence of a preservative. In the case of pharmaceutical creams, these are usually oil-in-water emulsions stabilized using a surfactant. Phenolic preservatives, e.g., parabens esters, are inactivated in the presence of nonionic surfactants, and this detrimental interaction can have serious consequences for preservation of the product (20). 

Microbial spoilage of emulsified products is avoided by the inclusion of appropriate amounts of a preservative in the formulation. Infected topical emulsions have been the cause of outbreaks of pseudomonal and other bacterial skin infections. The incorporation of preservatives into pharmaceutical emulsions is not without problems as most agents partition to the oily or micellar phases of complex systems some are inactivated by surfactants. 

Fig. 16.1 Section (xl.5) through an inadequately preserved olive oil, oil-in-water, emulsion in an advanced state of microbial spoilage showing A, discoloured, oil-depleted, aqueous phase B, oil globule-rich creamed layer C, coalesced oil layer from cracked emulsion D, fungal mycelian growth on surface. Also present are a foul taste and evil smell ...

Preservatives like benzalkonium chloride and parabens may be included in ophthalmic emulsions to prevent microbial spoilage of multi-dose ophthalmic nanoemulsions. The presence of... 

Biocides, although required in very small amounts, are often expensive and complex chemicals that are very labile to the hostile chemical environment of the polymerisation process and therefore their addition must be carefully controlled and monitored (Reeve, 1987 Conquer, 1993). The biocide is therefore added into the blender at a time determined when the temperature is low enough (<50°Q to prevent thermal degradation and when the free radicals have been consumed in the process (Conquer, 1993). This time is determined by a simple test to monitor the redox state of the emulsion. Under these conditions the biocide has the best chance of survival to allow it to perform its function as a long term preservative against microbial spoilage of the emulsion. The question of the stability of biocide active substances in the presence of redox chemicals is discussed later. 

Emulsions offer cost advantages in the delivery of water-soluble (or dispersible) flavorings since water is a very inexpensive solvent. The primary disadvantages of emulsions are that they are physically unstable and require preservation from microbial spoilage. Physical stability is not an issue with baker s emulsions since they are stabilized by the system viscosity. 

It has been known for many years that microbial contaminants may effect the spoilage of pharmaceutical products through chemical, ply sical or aesthetic changes in the nature of the product, thereby rendering it unfit for use (see Chapter 18). Active drug constituents may be metabolized to less potent or chemically inactive forms. Physical changes commonly seen are the breakdown of emulsions, visible surface growth on solids and the formahon of slimes, pellicles or sediments in hquids, sometimes... 

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