Nonsterile pharmaceutical products and microbial risks: Profile, sources, detection and control

Nonsterile pharmaceutical products are at risk from microorganisms [1]. The presence of organisms in medications not only provides an infectious hazard; the presence of spoilage organisms can alter the chemical, physical and organoleptic properties of the preparation or render the active ingredients ‘inactive.’

A particular problem is where certain nonsterile pharmaceuticals present selective environments allowing for the enrichment and subsequent dissemination of bacterial resistance-determinants [2].

This week’s article is a ‘back to basics’ one, looking at some of the microbial risk factors to be accounted for in the manufacture of nonsterile pharmaceutical products.

Determining microbial risks

For any nonsterile pharmaceutical product manufactured microbiological controls will vary. In determining what the microbial risks are, we need to understand [1,3,4]:

• Likely microbial contaminants,
• Microbiological susceptibility of the product including what happens in relation to the product formulation,
• What is likely to happen with contaminants over time (e.g., growing, remaining stationary or dying),
• The risk of toxic by-products,
• Patient population,
• Route of administration,
• Dose,
• Whether the product is multi-use.

To this, we can add the schema drawn by the late Scott Sutton:

The use of the product: hazard varies according to the route of administration (eye, nose, respiratory tract).        

The nature of the product: Does the product support growth?        

Does it have adequate antimicrobial preservation?        

The method of application.        

The intended recipient: risk may differ for neonates, infants, and the debilitated.        

Use of immunosuppressive agents, and corticosteroids.        

The presence of disease, wounds, organ damage.        

Based on this product knowledge we can determine the risks and controls required and develop a suitable product specification [5].

Product profile

Various products will have different susceptibility profiles. The susceptibility of products is determined by:

• Proportion of available water in the formula,
• Antimicrobials present in the formula,
• Antimicrobial steps in the manufacturing process (such as heating, filtration and so on).

Products containing high levels of water activity with low levels of antimicrobials are typically at the highest risk. Here, higher water activity means more water is available for organisms to grow. The water activity scale also informs us about the types of microorganisms that are likely to grow; for example, a water activity below 0.95 means that Gram-negative organisms are unlikely to proliferate. Interested readers should read the work of Tony Cundell on this topic [6].

For antimicrobial activity, the primary assessment is through the antimicrobial effectiveness test. An important consideration is with the recommended test panel; while the use of compendial strains is important, the panel may need to be expanded through risk assessment considering what might be in the manufacturing environment and which types of organisms could survive in the product. The expansion of the test panel can be through the use of additional organisms sourced from a culture collection or environmental isolates.

In developing an antimicrobial effectiveness test it is useful to understand the speed and extent of kill and the level of contaminants that might be present. Prevention of contamination should always be the primary control mechanism and this concept extends to the use of controls in the manufacturing environment.

Selecting a suitable antimicrobial is something that should be decided early on in the product development cycle and this consideration may require alternative antimicrobials to be considered, in line with product reformulation.

With the route of administration, this is best illustrated by two products prone to microbial growth – shampoo and eye drops. While both can support microbial growth, eye-drops present a greater risk because they enter the human body.

Detectability

Detecting low levels of microbial contamination is not easy; methods are limited and organisms are fastidious in terms of their growth patterns [7]. Uncertainty stems from dilution factor, plated volume, and microbial plate counts.

This again helps to place an emphasis upon control – certainly, a manufacturer cannot simply rely on testing alone to gain sufficient confidence that a product is safe. Rapid microbiological methods provide a means to improve accuracy and precision in relation to detection, such as PCR-based assays [8], especially when targeted to detect specific objectionable organisms of concern like members of the Burkholderia cepacian complex [9].

Invariably, detectable contamination in a batch requires high numbers of microbes or sparse numbers of antimicrobial resistant microbes.

Organisms that exhibit antimicrobial resistance pose a significant threat since product failures are not always detectable at release.

Contamination origins

Contamination can arise from diverse sources and pose a risk through different vectors. In a well-controlled process, direct contamination of products from the environment is less likely and few studies are able to draw a direct correlation between environmental contamination and product contamination.

In contrast, raw materials can often be a major source of contamination [10], including ingredient water. Another source arises from contaminated equipment or from improperly cleaned or dried equipment. Operator practices can be a source of sporadic contamination, more often of individual units rather than an entire batch (the problem here is that due to the statistical limitations of sampling, contamination during filling is more likely to be undetectable in routine testing).

Water

Of the different contamination origins, special attention needs to be paid to water. Where water contains organisms, these are generally Gram-negative bacteria, especially in water containing lower organic compounds such as purified water. Pseudomonads and other Gram-negative bacteria are often well adapted to grow in the low-nutrient environment of purified water. A concern with Gram-negative bacteria is a continual one, remaining an uninterrupted issue since Jimenez’s review of pharmaceutical product recalls some two decades ago [11]. Particular attention needs to be paid to aqueous products [12].

If water is left standing, or where sinks and outlets are not adequately controlled, organisms will grow.

Contamination risk

The primary risk factor is preservative-resistant organisms present in the product. This means the microbes may grow without restriction, reaching dangerous levels for the product user after release.

Most bacteria naturally occurring in water will not have preservative resistance since the population will not normally have come across a preservative before. However, where preservatives enter drains (as through waste ingredients or pharmaceutical products) a mix of water, product residues and bacteria is created. Invariably in this environment, a dilute solution of product preservatives is present. Here, the preservative levels are not sufficient to kill the organisms (and too many organisms may be present, or organisms are protected within a biofilm complex). This affords the bacteria time to activate resistance mechanisms. It may also be that the product provides a source of nutrients for the organisms (in addition to other nutrient sources). This means the organisms have food, water and an opportunity to express resistance – something that extends as the microbial community grows [13].

If organisms residing in environments like drains re-enter the manufacturing process (such as through backflow, splash back or mishandling of the drain), this introduces a potential product contaminant that is resistant to the preservative used in the pharmaceutical preparation. Other transfer routes include:

• Vacuum pumps (liquid ring pumps) are often used to suck product down the drain. If there was a loss of power, the flow could be reversed thereby pulling organisms into process equipment.
• Contamination of equipment by aerosols from the drain can occur; this is a particular risk should equipment that has been cleaned and which is undergoing drying become contaminated.
• During the cooling of the equipment after sanitization, physical forces can draw contents from the drain into the equipment as air contracts during the cooling phase (this occurs as particles lose kinetic energy and move closer together, leading to a decrease in air volume).
• Partial cleaning of equipment. If cleaning does not effectively remove all of the product residue creating a product-water mix and the creation of dilute antimicrobials enables organism resistance to develop.

• Similar weaknesses arise from the poor hygienic design of equipment, such as the presence of uncleanable crevices or parts, again leaving product residues or from leakage of valves and gaskets. Another issue can arise from poor equipment drainage.
• Condensation in bulk storage vessels/process vessels can occur, again serving to dilute product at the interface or on the equipment surface.

If the bacterium enters the product and demonstrates resistance, it has the opportunity to grow and increase in number (reaching levels that are dangerous for the user of the product).

Prevention

The main approach to a prevention strategy is understanding the product, process and equipment, including the order of flow. Hence, manufacturers should consider process improvements and microbial control strategies [14]. This provides invaluable information for conducting a risk assessment.

Risk areas to assess may include:

Raw materials and packaging materials        

Utilities (water, compressed gases, vacuum etc.)        

Hygienic design of equipment        

Operating environment and controls        

Cleaning and disinfection        

Validation and verification        

Microbiological testing (consider additional non-specified objectionable organism testing for aqueous nonsterile products).        

People        

Using risk tools like Hazard Analysis Critical Control Points (HACCP) enables the microbiologist to critically assess each step; to identify hazards; to assess hazards for severity and likelihood; and to determine the risk (to draw on Cundell again, there is a useful application in relation to a tableting facility) [15]. From these appropriate corrective measures can be put into place and the final control strategy produced.

Another key area is the design of equipment. With this, equipment needs to be easy to clean, fully drainable, and with the ability of the cleaning process to clean and sanitize all surfaces.

Summary

Contamination of nonsterile pharmaceuticals with microorganisms, irrespective of whether they are harmful or nonpathogenic, can deliver changes in physicochemical characteristics of the medicines. Those that are pathogenic can pose a serious risk to specific patient populations, especially those with weakened immune systems. This article has considered risk factors and measures to control selected species and overall bioburden, citing the importance of understanding the product and the process.

Tim Sandle is a pharmaceutical microbiologist. Please visit Pharmaceutical Microbiology Resources.

References

1. Sandle, T. Pharmaceutical Microbiology: Essentials for Quality Assurance and Quality Control, 2015, Elsevier, USA

2. M.C. De la Rosa et al. Resistance to the antimicrobial agents of bacteria isolated from nonsterile pharmaceuticals, J Appl Bacteriol (1993)

3. Denyer S, Baird R, editors. Guide to Microbiological Control in Pharmaceuticals. Chichester, UK: Ellis Horwood; 1990

4. Aulton ME. Pharmaceutics: The Science of Dosage Form Design. 2nd ed. London, UK: Churchill Livingstone; 2002

5. W. Manu-Tawiah et al. Setting threshold limits for the significance of objectionable micro-organisms in oral pharmaceutical products, PDA J Pharm Sci Technol (2001)

6. Cundell, T. The role of water activity in the microbial stability of nonsterile pharmaceutical drug products, European Pharmaceutical Review, Issue 1, 2015: https://www.europeanpharmaceuticalreview.com/article/29889/the-role-of-water-activity-in-the-microbial-stability-of-nonsterile-pharmaceutical-drug-products/

7. Tidswell EC, Tirumalai RS, Gross DD. Clarifications on the Intended Use of USP <61> Microbiological Examination of Nonsterile Products: Microbial Enumeration Tests. PDA J Pharm Sci Technol. 2024 Jun 28;78(3):348-357.

8. Bermond C, Cherrad S, Trainoy A, Ngari C, Poulet V. Real-time qPCR to evaluate bacterial contamination of cosmetic cream and the efficiency of protective ingredients. J Appl Microbiol. 2022 Mar;132(3):2106-2120

9. Dufour G, Lebel K, Bellemare J, Iugovaz I. Identification of Burkholderia cepacia Complex by PCR: A Simple Way. PDA J Pharm Sci Technol. 2023 Dec 7;77(6):485-497.

10. De La Rosa MC, Medina MR, Vivar C. Microbiological quality of pharmaceutical raw materials. Pharma Acta Helv. 1995;70(3):227–232. doi: 10.1016/0031-6865(95)00022-2

11. Jimenez L. Microbial diversity in pharmaceutical product recalls and environments. PDA J Pharm Sci Technol. 2007 Sep-Oct;61(5):383-99.

12. Torbeck L, Raccasi D, Guilfoyle DE, Friedman RL, Hussong D. Burkholderia cepacia: This Decision Is Overdue. PDA J Pharm Sci Technol. 2011 Sep-Oct;65(5):535-43. doi: 10.5731/pdajpst.2011.00793

13. Baylan O. Ba????kl??? Bask?lanm?? Hastalarda S?kl?kla Saptanan Bir F?rsat?? Patojen: Burkholderia cepacia Kompleksi [An opportunistic pathogen frequently isolated from immunocompromised patients: Burkholderia cepacia complex]. Mikrobiyol Bul. 2012 Apr;46(2):304-18

14. Santos AMC, Doria MS, Meirinhos-Soares L, Almeida AJ, Menezes JC. A QRM Discussion of Microbial Contamination of Nonsterile Drug Products, Using FDA and EMA Warning Letters Recorded between 2008 and 2016. PDA J Pharm Sci Technol. 2018 Jan-Feb;72(1):62-72. doi: 10.5731/pdajpst.2016.007252

15. Cundell, T. Microbial Contamination Risk Assessment in Nonsterile Drug Product Manufacturing and Risk Mitigation, In Eds. David Roesti, Marcel Goverde, Pharmaceutical Microbiological Quality Assurance and Control: Practical Guide for Non‐Sterile Manufacturing, 2019 https://doi.org/10.1002/9781119356196.ch2