Introduction:
In our environment microbes are present everywhere i. Air, water, soil etc.
These microbes are to cause spoilage of not only food products but also pharmaceutical products.
The spoilage of pharmaceutical products can result in serious health hazards to the consumers as well as cause financial problems to the manufacturers.
Pharmaceutical products are considered microbiologically spoiled when even low levels of pathogenic microbes or toxic microbial metabolites are present and detectable physical or chemical change have been noted in the product.
In short it can be defined as deterioration of pharmaceutical products due to microbial contamination.
Types of Microbial Spoilage:
Infection induced due to contaminated pharmaceutical products:
Pharmaceutical products may get infected from many sources like raw material, manufacturing, storage etc.
Such infected products when consumed causes the diseases.
E.g. Cholera, Pseudomonas infections, Botulism etc.
The common infections found in dosage form are summarized in Table no. 1.1.
Table no. 1.1 Common pathogens spoiling pharmaceutical products:
Physico-chemical spoilage:
In this kind of spoilage, there are some changes caused by microbial species and due to these changes the physical properties are also gets altered or deteriorate, thus it is called physico-chemical spoilage.
Viable growth: Microbial cells form a viable layer over the surface of pharmaceutical formulation.
This layer or the presence of microbial cells can be clearly seen by naked eyes.
layer of moulds over syrups or sugar containing products.
Change in Color of the formulation: Occurs due to the change in the components chemical nature.
Surface decoloration of tablets containing biological products by some mould.
Gas production: Some microbe contaminants in pharmaceutical formulations produces gases by their metabolic activities and form gas bubbles and foam over the formulation.
e.g. in carbohydrates containing formulations like syrups by yeasts.
Physical Spoilage:
These changes in physical appearance are caused by microbial activities in the formulation.
Cracking of emulsion: Microbes eat off the emulsifying agent causing instability of emulsions resulting in separation of phases.
Odor changes: Microbes due to their activity in the pharmaceutical product impart smell.
e.g. Toluene smells due to spoilage of Balsam of Tolu by Penicillium species.
Smell of geosmin to water phases by Actinomycetes contamination.
Biological spoilage:
Microbial contamination of the products result in formation of chemicals in the products due to microbial metabolic activity, this is terms as Biological spoilage.
Mainly two types of chemicals are produced by microbes,
Microbial Toxins.
Microbial Metabolites.
Microbial Toxins: Endotoxins produced by some gram –ve bacteria like E.coli.
Microbial Metabolites: Different types of amines and organic acids.
Chemical spoilage:
This occurs due to various types of chemical reactions, mediated by contaminating microorganisms.
The ingredients in formulation that are susceptible for chemical damage by microbial actions are tabulated in Table 1.2.
Table 1.2 Susceptibility of pharmaceutical ingredients to microbial contamination
Factors affecting microbial spoilage:
By understanding various factors promoting growth of microbes in the formulation it is possible to manipulate the formulations and to avoid their microbiological spoilage without affecting the patient acceptance and therapeutic efficacy of the formulation.
Some identified factors that affect microbiological spoilage of pharmaceutical products are as follows,
Size of contaminant inoculum
Nutritional factors
Moisture content
pH
Storage temperature
Redox potential
Packaging design
Size of contaminant inoculum:
The rate of deterioration of a pharmaceutical product depends on the size of microbial population in the product.
Lower microbial population size shows lesser degradation changes as compared to large size populations.
However, inoculum size alone is not always a reliable indicator of likely spoilage potential.
A very low level of pseudomonas in a weakly preserved solution may suggest a greater risk than tablets containing high numbers of fungal and bacterial spores.
Nutritional factors:
Most of the organic and inorganic ingredients act as potential carbon or nitrogen substrates for microbial growth.
The complexity of many formulations offers considerable nutritional variety for a wide range of microorganisms.
The use of crude vegetable or animal products in a formulation provides an additionally nutritious environment.
Even demineralised water prepared by good ion-exchange methods will normally contain sufficient nutrients to allow significant growth of many waterborne Gram-negative bacteria such as Pseudomonas spp.
Moisture content:
By measuring a product’s water activity (Aw ), it is possible to obtain an estimate of the proportion of uncomplexed water that is available in the formulation to support microbial growth.
Most microorganisms grow best at high water activity.
Hence, formulation can be protected from microbial attack by lowering their water activity with addition of suitable levels of sugars, polyethylene glycols or sodium chloride or by drying.
pH:
Extremes of pH prevent microbial attack.
Around neutrality, bacterial spoilage is more likely, with reports of Pseudomonads and Gram-negative bacteria growing in antacid mixtures, flavoured mouthwashes and in distilled or demineralised water.
Above pH 8 (e.g. with soap-based emulsions) spoilage is rare.
In products with low pH levels (e.g. fruit juice-flavoured syrups with a pH 3–4), mould or yeast attack is more likely.
Yeasts can metabolize organic acids and raise the pH to levels where secondary bacterial growth can occur.
Storage temperature:
Spoilage of pharmaceuticals could occur potentially over the range of about -20°C to 60°C •
The particular storage temperature may selectively determine the types of microorganisms involved in spoilage. •
A deep freeze at -20°C or lower is used for long-term storage of some pharmaceutical raw materials and short-term storage of dispensed total parenteral nutrition (TPN) feeds prepared in hospitals. •
Reconstituted syrups and multi-dose eye-drop packs are sometimes dispensed with the instruction to ‘store in a cool place’ such as a domestic fridge (8°–12°C), partly to reduce the risk of growth of contaminants inadvertently introduced during use.
Redox potential:
The ability of microbes to grow in an environment is influenced by its oxidation-reduction balance (redox potential), as they will require compatible terminal electron acceptors to permit their respiratory pathways to function.
The redox potential even in fairly viscous emulsions may be quite high due to the appreciable solubility of oxygen in most fats and oils.
Packaging design:
Packaging can have a major influence on microbial stability of some formulations in controlling the entry of contaminants during both storage and use.
Considerable thought has gone into the design of containers to prevent the ingress of contaminants into medicines for parenteral administration, owing to the high risks of infection by this route.
Self-sealing rubber wads must be used to prevent microbial entry into multi-dose injection containers following withdrawals with a hypodermic needle.
Where medicines rely on their low Aw to prevent spoilage, packaging such as strip foils must be of water vapour-proof materials with fully efficient seals.
Cardboard outer packaging and labels themselves can become substrates for microbial attack under humid conditions, and preservatives are often included to reduce the risk of damage.