Microbial Spoilage of Pharmaceutical Products


Spoilage is chemical and physicochemical degradation of pharmaceutical products rendering it unsuitable for use. Microbial spoilage can be caused by bacteria, yeasts fungi. It is often difficult to prevent the contamination of a pharmaceutical product during manufacture or contamination of individual components used for the manufacture of the final product. Also, a pharmaceutical product can be contaminated during used by the patient, during dispensing by the pharmacist and even by the medical staff. This problem is often controlled by the use of:

  • sterile unit dosage forms.
  • use of multiple multidose components to minimize the entry of contaminants.
  • to kill microbial contaminants in order to reduce the risk of microbial spoilage.

Types of Microbial Spoilage

  1. Physico-chemical spoilage: This type of spoilage changes the physico-chemical properties of the pharmaceutical product involved.
  2. Physical Spoilage: Cracking of emulsion, Odor changes and other changes in Pharmaceutical Products as a result of microorganisms is termed physical Spoilage. Examples of this include Toluene smells due to spoilage of Balsam of Tolu by Penicillium species and Smell of Geosmin to water phases by Actinomycetes contamination.
  3. Biological spoilage: Spoilage of pharmaceuticals may produce some undesirable and dangerous molecule which has undesirable biological effects. Some microbes may produce toxins, pyrogens or other harmful metabolites.
  4. Chemical spoilage: This type of spoilage occurs due to various types of chemical reactions mediated by contaminating microorganisms in the Pharmaceutical Products.

Indications of microbial spoilage

A pharmaceutical product may be regarded as microbiologically spoilt if:

  • there are low levels of acutely pathogenic microorganisms or higher level of opportunist pathogens present
  • presence of toxic microbial metabolites even after the death of the original contaminants.
  • presence of physical or chemical deteriorations in the product.

Consequences of spoilage

  • Lack of patronage of the product
  • Financial loss to the manufacturers or suppliers.
  • Litigation by the users if damage or body harm is caused to the user.

Examples of spoilage Microbial organisms

The widely reported pharmaceutical contaminating Microbial organisms are:

  • Salmonella spps contaminants
  • Pseudomonas aeruginosa contaminants
  • Klebsiella spp contaminants
  • Candida spp contaminants
  • Fungal/mould contaminants

Pharmaceutical contaminants are fastidious in nature. They may not be able to replicate in most medicines but remain viable and infective for an appreciable time that when introduced into the human body they can regain their pathogenic status.
Salmonella infections have occurred from tables and capsules of yeast, carmine pecreatin, thyroid extract and powedered regetable drugs. In these instances the low level of pathogens obtained in these finished drugs were traced to have originated from the raw materials during there manufacture. In most cases contaminants arose from infected human carriers or traced to raw materials in the ingredients of the pharmaceutical products. Contaminants isolated from pharmaceutical have ranged from true pathogens such as Clostridum tetani, to opportunist pathogens such as Pseudomonas aeruginosa and other Gram-negative organisms that are capable of causing diseases under special circumstances.

Examples of Most Contaminated Pharmaceutical Products

Most contaminated products have been

  1. Disinfectants, antiseptics, powders, tablets etc.
  2. Products with non-nutrition components such as creams, lotions containing carbohydrates, amino acids, vitamins and appreciable quantities of water have been incriminated.

Some Products and and their Common Contaminants

  1. Oral mixtures and antacids (Kletsiella spps)
  2. Tablets (Bacillus faealis staph aureus, Ps. aueruginos).
  3. Products such as saline solution Ps. Aueruginos)
  4. carmine powder (Salm.cubane);
  5. Hand Cream (Kletsiella Pneumonial)
  6. pepper mint water (Ps. aueruginos)
  7. Chlorlexidine-ctrimide antiseptic solution (Ps. cepacia).
  8. Intravenous fluids (Pseudomonas spp, Enterobacter spp, Erwinia spp);
  9. Pancreatine powder (salm. agona);
  10. contact lens solution (Enterobacte spp and Serratia marcescens);
  11. surgical dressing (clostridium spp);
  12. aqueous soap (Ps. Stutzeri);
  13. creams and ointments (candida spps) intravenous and
  14. oral solutions (candida spps).

The outcome of the use of contaminated product varies from patient to patient. For example, a patient with serious burns will be at risk of Staphylococcal infection and Pseudomonas aerugimosa. Contaminated injected products may induce severe generalized bacteraemic shock and in some cases death of patients in immune compromised situations. Powders used to dress sores, ulcers, wounds etc. can further induce their brakdowns and delay healing. Many eyes have been lost due to infections by contaminants in improperly designed ophthalmic solutions containing actively growing Pseudomonas aerugimosa as contaminants.
Patients’ immuno compromised as a result of anti-neoplastic chemotherapy or as an aid to transplant surgery, life-threatening infections have been at risk. High incidence of localized infections at sites of catheter insertion can be due to contamination of the site of injections. Candida spp have induced septicaemia from contaminated infusion fluids. Even major toxic metabolites are pyrogens (liberated from Gram-negative bacteria and blue-green algae (Cyamobacteria) as lipopolysaccharides.
However, acute bacterial toxins associated with food poisoning episodes have not been commonly reported amongst pharmaceutical products, although toxigenic fungi such as aflatoxin-producing aspergilla and aflatoxins have been detected. It is common knowledge that metabolic products of microbial deterioration are very unpleasant, if not toxic, could still deter the use of a medicine if it is present even in small quantities.

Chemical and Physiochemical Deterioration of Pharmaceutical Products

Pharmaceutical formulations are subject to microbial degradation because of their conductive physico-chemical characteristics due to the inclusion of crude animal or vegetable drugs or extracts, inclusion of assortments of nutrients and inorganic components.
The overall rate of deterioration of a chemical depends on

  1. its chemical structure.
  2. physicochemical characteristics of a particular environment in which the product is formulated.
  3. type and quantity of contaminant microbes present
  4. Whether the metabolic fragments of the microbial contaminants can yield materials and energy for further microbial growth and the synthesis of more degradative enzymes.

Pharmaceutical ingredients susceptibility and microbial attack

a. Surface active agents

  1. Anionic surfactant such as alkali metal and amine soaps of fatty acids are alkaline in nature and are generally protected by their slightly alkaline formulations although readily degraded in sewage. Alkyl and alkylbenzenes, sulphonates and sulphate esters are metabolized by w-oxidation of their terminal methyl groups followed by sequential β- oxidation of the alkyl chains and fission of aromatic rings. Sulphonate and sulphate ester residues are degraded to sulphate, although sulphonate residues are significantly more recalcitrant than the esters. In shampoos, anaerobic sulphate – reducing bacteria reduces sulphate to hydrogen sulphide.
  2. Non-ionic surfactants such as alkylpolyoxyethylene alcohol emulsifiers are readily metabolized by several microorganisms. Increasing chain length of and branching of these products decreases the ease of attach. Alkylphenol polyoxyethylene alcohols are attached as above although are more resistant.
  3. Cataionic surfactants used as antiseptics and preservatives are slowly metabolized in sewage and have been reported to support the growth of Gram-negative bacteria even at their own expense.
  4. Ampholytic surfactants based on phosphatides, betaines and alkyl-amino-substituted amino acids are readily degradable.

b. Organic Polymers

Depolymerisation of several thickening and suspending agents used in pharmacy by special extra-cellular enzymes occur. It plays significant role in the integrity of polymers and in pharmaceutical preparations.
Example of such degrading enzymes with their substrates are:

  1. Amylase (starches)
  2. Cellulase (carboxymethyl cellulose) but not alkylcellulose pectinare (pactins).
  3. Pectinase (pectins)
  4. Uromidase (tragacanth and acacia)
  5. Dextranases (dextrans)
  6. Proteases (proteins)

Agar is used as an inert support for culture media because its enzymic deploymerisation is rare although do exist. Polyethylene glycols are easily degraded by sequential oxidation of hydrocarbon chains. Polymers used in plastic packaging are very recalcitrant to biodegradation with the exception of cellophane which is subject to cellulolytic attack in some circumstances.

c. Humectants

Glycerol and sorbitol in pharmaceuticals readily support microbial growth unless present in high concentration.

d. Fats and Oils

Fats and oils are readily biodegraded in aqueous formulations. Fungal growth has been reported to be present in condensed moisture films on the surface of oils or if water droplets contaminate the bulk phase during storage.
Lipolytic rupture of triglycerides liberates glycerol and fatty acids. The released fatty acids that undergo β-oxidation of the alkyl chains produce odorous ketones.

e. Sweetening, flavouring and colouring agents

Many sugars and other sweetening agents used in pharmacy are ready substrates for microbial attack, except very concentrated stock solutions of sugar (syrups) with low water activities are more resistant to microbial attack. However, reports of spoilage by growth of osmophilic yeasts in them are not uncommon.
Aqueous solutions of stock solutions of flavouring agents e.g. peppermint water and chloroform water, colouring agents such as amaranth or tartazine readily support growth of bacteria and yeast. The use of single stock solution of flavouring agents are no longer recommended although colouring agent may still be used for extemporaneous dispensing.

f. Therapeutic agents

Many therapeutic compounds are known to be very degradable with destruction or marked charge in their therapeutic efficacy.

  • Alkaloids: Morphine, streychine, atropine,
  • Analgesics: aspirin, paracetamol,
  • thalidomide, barbiturates, mandelic acid, steroid esters etc. can be metabolized and have served as substrates for microbial growth.
  • Appreciable loss of potency of some alkaloids e.g atropine eye drops, degradation of aspirin and paracetamol in aqueous formulations have been encountered.

Aspirin yields irritant salicylic acid, penicillin produces inactive products by β-lactamase, chloramphenol is degraded by chloramphenial acetylase etc. Dicophane (DDT, a chlorinated hydrocarbon) are highly recalcitrant.

g. Preservatives and Disinfectants

Several organic preservatives and disinfectant are metabolized by many bacteria and fungi and may even serve as growth substrates at concentration well below “use” levels. This often occurs in sewages and effluents although quarternary ammonium antimicrobials are only degraded slowly. Organomercurial preservative eg phenylmecuric nitrate or acetate could pose a significant environmental hazard on microbial conversion to the toxic ethylemercury and methylmercury products to man via an ascending food chain. Microbial degradation at “use” levels of antimicrobial agent has not been much reported but are known to occur in chlorhexidine cetrimide, phenolics, phenylethylalacohol and benzoic acid. Benzakonum chloride is occasionally utilized at “use” concentrations. p-hydroxybenzoate (4-hydroxybenoate) esters at concentrations formerly recommended for eye drop preservation (0.01% w⁄v have been reported to be broken down by Pseudomonas and other related bacteria, even using them as growth substrates eg. Ps.aeruginosa.

Observable Effects of Microbial Attack in Pharmaceutical Products

Microbial spoilage in chemical or physicochemical terms occurs when a significant growth of microbial contamination is observed in the product. Microbial spoilage in pharmaceutical products are often localised in surface moisture films or unevenly distributed within the bulk of viscous formulations.

Early indicative (indication) signs are:

  1. Release of unpleasant tasting or Smelling metabolities such as sour fatty acids, ketones such as “fishy” amines like rotten eggs “ammonia like”, bitter nausic “earthly” or alcoholic tastes and smells.
  2. Discolouration of products by various microbial pigments to the extent that polythene may exhibit a pink or greenish colouration when coloured by fungi.
  3. Depolymerisation of thickening agents resulting in loss of viscosity and sendimentation of insoluble ingredients.
    The depolymerisation of sugar or surfactant molecules can produce viscous, shiny masses in syrups and shamposs. In creams, “gritty” texture can be produced as a result of depolymerisation
  4. The accumulation of acidic or basic metabolites can produce appreciable changes in pH. It has been found that yeast attack of acidic ingredients can raise the pH to a level that is sufficiently enough to allow subsequent growth of bacterial contaminants that were previously inhibited by low pH levels. In viscous formulations, bubbles of gaseous metabolites can accumulate and destroy the integrity of the product.
  5. Physicochemically, complex formulations such as oil/water (o/w) physical emulsions are often subject of microbial spoilage as the metabolism of the surfactants and suspending agent accelerate the creaming of oil globules.

The lipolytic release of fatty acids will lower the pH and encourage coalescence of droplets with cracking of the emulsion and souring of taste.
Bubbles of metabolite gas may also become trapped in the product with emerging unpleasant pigment discolouration.

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