Contamination of medicinal products: preservatives

Which medicinal products are sterile vs non sterile

Sterile: Ophthalmic (eye), parenteral (beyond intestine) e.g. single use sterile packs

Non sterile: Oral, rectal, topical, inhaled

What does non sterile mean

Limits on number of contaminants and don’t affect product quality

Absence of specific microbes

What factors can affect how well a product is sterilised

• Aqeuous/ non-acqeueous

• Use of product, hazard can vary according to route

• Nature of product e.g. may support microbial growth well in presence of preservatives

• Presence of disease, wounds, organ damage

• Intended recipient e.g. child vs adult

Which organisms have the most resistance vs least resistance to sterilizing agents and processes

What is bacteria

• No membrane bound organelles

• Small: 0.5-5um

• Divided into gram +ve, gram -ve

• Mostly non-pathogenic but some are

Compare the structure between gram positive and gram negative bacteria

Describe the 5 stages of formation of biofilms

1. initial attachment

2. irreversible attachment

3. microcolony formation

4. maturation

5. dispersal

What’s the issue with biofilms in medicine

Responsible for majority of infections

Grows on medical devices

Grows on medical surfaces

Grows on air/water even dialysis equipment

What is meant by MIC

Minimum inhibitory concentration

The lowest concentration of antibiotic that inhibits growth of bacteria

The lower the MIC the more effective

What is bacterial sporulation

• A survival strategy when nutrient sources are depleted

• Mechanism used by some G+ve bacteria

• Spores are resistant to heat, radiation, desiccation, chemical agents so can survive for years

What are the key stages in bacterial sporulation and how does it differ from regular cell division?

Cell Division (Growth Cycle):

In favorable conditions, bacteria undergo normal cell division through binary fission.

Steps: Growth → Septum Formation → Two identical daughter cells.

Sporulation (Stress Response):

When conditions are unfavorable, bacteria switch to sporulation, a survival mechanism.

Key stages:

Asymmetric Cell Division: Forms a smaller forespore and larger mother cell.

Engulfment: The mother cell engulfs the forespore.

Cortex Formation: A thick protective layer forms around the spore.

Spore Coat: Additional protective layers develop.

Cell Lysis: The mother cell dies, releasing the mature spore.

Germination: The spore can later germinate into an active bacterial cell when conditions improve.

Describe fungi

• Eukaryotic

• 3 types: yeast, multicellular filamentous mould, macroscopic filamentous fungi

What is the medical significance of fungi

Pathogenic: candida, aspergillus, dermatophytes

Non pathogenic: Penicillin produced by penicillium

What can lead to the recall of medicinal products

Recall due to microbial contamination usually by bacteria

Rarely:

Viruses: animals + humans

Protozoa: unsterilized contact lenses

Prions: blood

What are the consequences of microbial contamination

Health hazard: toxins can cause disease

Spoilage: break down chemical actives, loses aesthetic appeal, financial loss

How do products become contaminated

All products potentially exposed to micro-organisms during storage

Multiple-use products potentially exposed to microorganisms during use

Compare the different types of pharmaceutical products, sterile, single/multiple use

What do preservatives do

• Decrease the risk of microbial contamination through product shelf life

• Properties: Broad spectrum antimicrobial activity, non-toxic/non-irritating, chemical stability, compatibility with formulation, long acting but not fast acting, active at low concentrations

• Must not mask poor manufacturing

Which preservative agents are used in the uk

Organic acids

Parabens

Esters

What are the key differences between organic acids and parabens in pharmaceutical formulations?

• Organic Acids:

  • Limited by pH dependence; effective up to their pKa.

  • Example: Benzoic acid (pKa 4.2).

  • Used in oral products (tablets, capsules) at concentrations of 0.01-0.15%.

• Parabens:

  • Overcome the pH dependence of organic acids.

  • Example: Methyl paraben (pKa 8-8.5).

  • Used in oral products (tablets, capsules) at concentrations of 0.01-0.02%.

  • Often used in combination, but have low solubility and a slow rate of kill.

How is the effectiveness of preservatives tested in products?

• Challenge Test:

  • Add bacteria or fungi to the product in its final container.

  • Test organisms:

    • Bacteria: Pseudomonas aeruginosa, Staphylococcus aureus, Escherichia coli

    • Fungi: Aspergillus niger, Candida albicans, Zygosaccharomyces rouxii

• Incubation:

  • Keep product for 28 days at a specific temperature.

• Result:

  • Measure if microbes are killed or reduced enough to meet acceptance criteria.

What is the suspension test

A simpler form of challenge test

Tests for biocides

Procedure: Microorganism added to antimicrobial, samples taken at specific time points, inoculated in broth with a neutralizer

Test for growth/ cloudiness

What is a neutralising broth

Neutralises a broad spectrum of antiseptics, disinfectants and preservatives

How do we calculate what portion of microorganisms were eliminated by preservatives

log reduction

Challenge test criteria of acceptance

What factors affect preservatives

Intended application

No. type microorganisms present: e.g bacteria and fungi affect oral products

safety, stability, cost, shelf life

microenvironment

properties of chemical agent

What is meant by intended application

If the product is sterile vs non sterile

What is the drug’s route of administration

Moisture content

Susceptibility to attack

What is meant by safety, stability and cost

What is meant by microenviorment

• availability of preservative e.g. partitioning, permeation, interaction with formula

• Moisture

• Storage temperature

what is meant by physiochemical properties of a product

pH of a product, affects ionisation

Concentration/ dilution of the preservative, affects toxicity