The safety of non-sterile products cannot be ignored in the fast-moving world of pharmaceuticals. Each day millions take tablets, creams and syrups to improve their health without giving any afterthought to invisible risks lurking within. How can we ensure that these products are free from harmful levels of bacteria and fungi? The answer lies in the USP61 test for non-sterile products. 

Understanding Non-Sterile Pharmaceutical Products

Non-sterile products differ from sterile products as they are not required to be completely free of microorganisms. However, in non-sterile products microbial load should not exceed the safety limit that might lead to deterioration and ineffectiveness and may be harmful to the consumers.  Therefore regulatory bodies insist on microbiological testing which helps determine the safety and quality of these products. USP61 applies to a wide range of non-sterile pharmaceutical products such as:

• Oral Medications: Tablets, capsules, syrups and suspensions.

• Topical Products: Creams, ointments, gels and lotions.

• Nasal Sprays: Non-sterile nasal decongestants and allergy sprays.

• Suppositories: Rectal and vaginal suppositories.

• Medicated Powders: Powders used orally or topically.

Overview of USP 61

USP61 or the United States Pharmacopeia’s Microbial Enumeration Test specifically developed to provide the count of viable aerobic bacteria and fungi in non-sterile pharmaceuticals. USP61 test for non-sterile products prescribes standards and procedures by which these products shall be evaluated for their compliance with established microbial quality standards to ensure consumer safety. The test forms part of a broader framework within the pharmacopeial standards and has undergone revision to keep abreast with technological advancement in the microbiological testing area.

How USP 61 Works

Testing Process in USP 61

Several methods for microbial enumeration are described in the USP61 test for non-sterile products, each of which is suited to different types of non-sterile pharmaceutical products. The three primary methods include:

1. Membrane Filtration: It is best applied for liquid products. The sample is passed via a filter with a nominal pore size of 0.45 µm which retains the microorganisms. The filter is then transferred to a culture medium where the microorganisms are incubated and counted.

2. Plate Count Methods: These methods employ either of two procedures: the technique of Pour-Plate or the method of Surface-Spread:

• Pour-Plate Method: The sample is mixed with molten agar and poured into Petri dishes. When the agar has solidified/polymerized the plates are incubated and colonies growing within the medium are counted.

• Surface-Spread Method: A small amount of sample is distributed on the surface of an agar plate that has been previously prepared. The plate is incubated and the colonies grown on the surface are counted.

3. Most-Probable-Number (MPN) Method: This statistical technique is useful when microbial contamination is expected to be low. Serial dilutions of the sample are inoculated into multiple tubes of broth media and the presence or absence of microbial growth in these tubes is used to estimate the most probable number of microorganisms in the original sample.

Specific Test Organisms

USP61 test for non-sterile products requires testing against specific microorganisms known to be potential contaminants in non-sterile products. These include:

• Staphylococcus aureus: Contamination risks due to improperly manufactured or handled topical creams and ointments.

• Pseudomonas aeruginosa: Commonly found in non-sterile pharmaceutical products that contain water or are water-based like eye drops and nasal sprays

• Candida albicans: Commonly found in non-sterile pharmaceutical products that are susceptible to fungal contamination, particularly those that contain ingredients prone to moisture retention or are exposed to environments such as oral suspensions and syrups

• Escherichia coli (E. coli): Typically associated with contamination of products that involve raw materials or components derived from natural sources, particularly those that are water-based or contain botanical extracts.

• Aspergillus niger: Tablets and capsules, especially those containing starches, sugars or other organic materials, can provide a growth medium for fungi like Aspergillus niger if exposed to moisture.

These organisms are detected to validate the microbial enumeration test’s ability to detect contaminants in the product tested.

Incubation Times and Conditions

Conditions and time of incubation are important in USP61 tests for non-sterile products to identify and enumerate microorganisms accurately. The general incubation parameters are as follows: 

Total Aerobic Microbial Count (TAMC)

• Incubation Medium: Soybean-Casein Digest Agar (SCDA)

• Incubation Temperature: 30-35°C

• Incubation Duration: 3-5 days

Total Yeast and Mold Count (TYMC)

• Incubation Medium: Sabouraud Dextrose Agar (SDA)

• Incubation Temperature: 20-25°C

• Incubation Duration: 5-7 days

The standardized incubation conditions must allow the tested microorganisms to proliferate to ensure accurate enumeration.

Passing criteria

The passing criteria for USP61 test for non-sterile products are based on the acceptance limits established for TAMC, TYMC and specified microorganisms. It depends on the nature of the product involved, dosage form and its intended use. These mostly include colony-forming units (CFU) per gram or milliliter of product.

The passing criteria of USP61 microbial enumeration tests are as follows :

• For the product with a microbial limit of 10¹ CFU, the maximum acceptable count becomes 20 CFU.

• For the product with a microbial limit of 10² CFU, the maximum acceptable count becomes 200 CFU

• For the product with the microbial limit of 10³ CFU, the maximum acceptable count becomes 2000 CFU.

The microbial limits detailed under passing criteria apply to both Total Aerobic Microbial Count (TAMC) and Total Yeast and Mold Count (TYMC). The product passes the USP61 test for non-sterile products if the microbial count falls within these prescribed limits. If the microbial count exceeds the limit then the product fails. 

Ensuring Compliance with USP 61

Importance for Manufacturers

For manufacturers to ensure their non-sterile products meet safety standards it is important to adhere to the USP61 test for non-sterile products. It is required to prevent product recalls, legal consequences and reputational damage. Ensuring that microbial quantity is within safety limits will protect the consumers, more importantly the immunocompromised individuals.

Documentation and Validation

Manufacturers need to maintain comprehensive documentation of their microbial testing activities, including the corresponding results of USP 61. This documentation is necessary in case of regulatory audits and also makes sure that the products being provided to end users meet safety standards. Furthermore, process validation ensures the reliability of results.

At Microbe Investigations Switzerland (MIS), we offer expert testing and validation services for your non-sterile pharmaceutical products to comply with USP 61. Contact us today to safeguard your products and ensure they remain safe for consumers.