1. Introduction

Safety and quality of pharmaceutical drugs depend on the standard testing procedures that drug manufacturers follow based on the guidelines of various pharmacopeia. A pharmacopeia is a combination of multiple guidelines and drug quality criteria¹. The acceptance criteria for microbial contamination tests for non-sterile drug monographs in various pharmacopeias are essential criteria in the pharmaceutical industry to ensure that the drugs are free of certain microorganisms². Among the different types of pharmaceutical products on the market, oral tablets, capsules, active ingredients, oral liquids, and topical formulations are not required to be sterile. However, they must meet strict microbiological quality control standards to ensure that they are within the acceptance criteria of microbial tests³.

The importance of microbiological quality in non-sterile medicines arises from the potential risks posed by microbial contaminants. These risks include product spoilage, reduced effectiveness, and, in extreme cases, patient harm. Microbial contamination in medicines can change the physiological and chemical properties of drugs, causing the drug to be infectious or toxic^4,5. Therefore, all non-sterile medicines must be free of viable pathogenic microorganisms. Some microbial sources produce toxins as a result of metabolic activities, leading to conditions such as severe diarrhea, abdominal pain, gastroenteritis, and pneumonia^6,7.

This review explores the concept of microbial contamination in non-sterile medicinal products, the associated risks, and the testing methods adopted in various pharmacopeias: Indian Pharmacopoeia (IP), United States Pharmacopeia (USP), European Pharmacopoeia (Ph.Eur), British Pharmacopoeia (BP), Japanese Pharmacopoeia (JP), Chinese Pharmacopoeia (CP), and the International Pharmacopoeia (by World Health Organization). It establishes specific acceptance criteria for regulating the microbial quality of non-sterile products^8,9. It provides a comparative analysis of the acceptance limits for microbial contamination tests as defined in the major pharmacopeias, highlighting their similarities, differences, and the impacts on global drug manufacturing and the global pharmacopeias¹⁰.

2. Scope and methodology

The data for this review article were sourced from various pharmacopeia websites. Out of the 3,152 monographs listed in IP, 2,421 were reviewed. Among these, 951 were dedicated to active pharmaceutical ingredients (APIs), including 16 for non-sterile products; 1,247 focused on drug formulations, with 21 specifically addressing non-sterile formulations; and 164 were excipient monographs, with 22 monographs related to non-sterile products. Additional information was gathered through online search engines such as Google and PubMed, as well as local library resources from the Indian Pharmacopoeia Commission.

A pharmacopeia is established to ensure the safety, efficacy, and quality of pharmaceuticals while preventing inconsistent marketing. Several countries have introduced their own national pharmacopeias¹¹, such as IP 2022, USP 2024, BP 2024, Ph.Eur 11^th edition, JP 18^th edition, CP 2015, and International Pharmacopoeia 11^th edition. This review focused on the specific criteria outlined in the pharmacopeias and the chapters referring to microbial contamination in non-sterile products. The microbial contamination acceptance criteria of non-sterile products are generally stated in Chapter 2.2.9 in IP 2022, as discussed in Table 1, while the acceptance limit of specific microbial contamination is mentioned in 59 monographs in IP 2022, as overviewed in Table 2¹².

3. Overview of major pharmacopeias on microbial contamination standards

3.1. Indian Pharmacopoeia

As per the latest edition of IP (IP 2022), standards for microbial contamination have been compiled. For example, the bacterial count and fungal count determination, the use of specified microorganisms, and the acceptance criteria for the microbiological quality testing methodology for non-sterile products are mentioned in Chapter 2.2.9, “Microbial Contamination in Nonsterile Products”¹³. Meanwhile, the general microbiological quality requirements for tablets, capsules, oral liquids, and gels are listed in Volumes II and III of IP 2022¹².

3.2. United States Pharmacopeia

The microbial enumeration for non-sterile products is discussed in Chapter 61 in USP 2024, “Microbiological Examination of Nonsterile Products: Microbial Enumeration Tests.” Tests for specified microorganisms are discussed in Chapter 62, “Microbiological Examination of Nonsterile Products: Tests for Specified Microorganisms.” For assessing the acceptance criteria for pharmaceutical preparations, Chapter 1111, “Microbiological Examination of Nonsterile Products: Acceptance Criteria for Pharmaceutical Preparations and Substances for Pharmaceutical Use,” is documented in the current version of USP¹⁴.

3.3. European Pharmacopoeia

In the Ph.Eur 11^th edition, microbial enumeration is discussed in Chapter 2.6.12, “Microbiological Examination of Non-Sterile Products: Microbial Enumeration Tests”¹⁵. Specified microorganisms are discussed in Chapter 2.6.13, “Microbiological Examination of Non-Sterile Products: Test for Specified Micro-organisms”¹⁶. Chapter 5.1.4 is titled “Microbiological Quality of Non-Sterile Pharmaceutical Preparations and Substances for Pharmaceutical Use”^17,18.

3.4. British Pharmacopoeia

In the current edition of BP, quality testing methodology for microbial enumeration and specified microorganisms is discussed in Appendix XVI B, “Microbiological Examination of Non-sterile Products”¹⁹. Similarly, the acceptance criteria are discussed in Appendix XVI D, “Microbiological Quality of Non-sterile Pharmaceutical Preparations and Substances for Pharmaceutical Use”^20,21.

3.5. Japanese Pharmacopoeia

In the 18^th edition of JP, methodology for microbial enumeration and specified microorganisms is documented in Chapter 4.05, “Microbiological Examination of Non-sterile Products”²². The acceptance criteria are discussed in Chapter G4-1-170, “Microbial Attributes of Non-sterile Pharmaceutical Products”^23,24.

3.6. Chinese Pharmacopoeia

In CP 2015, microbial enumeration is discussed in Chapter 1105, “Microbiological Examination of Non-sterile Products: Microbial Enumeration Tests”²⁵. Tests for specified microorganisms are discussed in Chapter 1106, “Microbiological Examination of Non-sterile Products: Test for Specified Microorganisms”²⁶, and the acceptance criteria are discussed in Chapter 1107, “Microbiological Acceptance Criteria of Non-sterile Pharmaceutical Products”^27,28.

3.7. International Pharmacopoeia

In the current edition of the International Pharmacopoeia, Chapter 3.3.1, “Microbial Enumeration Tests” is dedicated to microbial enumeration. Tests for specified microorganisms are discussed in Chapter 3.3.2, “Test for Specified Microorganisms.” Similarly, the acceptance criteria are discussed in the supplementary information under the title, “Microbiological quality of non-sterile products: recommended acceptance criteria for pharmaceutical preparations”²⁹.

4. Results

The microbial limit acceptance criteria for microbiological quality of pharmaceutical preparations vary significantly depending on the route of administration and pharmacopeias (Tables 1 & 2). The related microbial contamination acceptance limit data were reviewed and compiled from several pharmacopeias. IP comprises a total of 951 monographs in APIs, with only 16 monographs reported with microbial acceptance limits; 1,247 monographs in formulations, with only 21 monographs reported with acceptance criteria; and 164 monographs in excipients, with only 22 monographs reported with microbial contamination acceptance limits^12,30 (Table 2 and Figure 1). Meanwhile, USP comprises 38 monographs of non-sterile products discussing microbial limit acceptance criteria, including 10 for APIs, 11 for formulations, and 17 for excipients¹⁴. Ph.Eur comprises 27 monographs of non-sterile products referring to microbial contamination acceptance limits, including 8 for APIs and 19 for excipients, while BP comprises 29 similar monographs, including 9 for APIs, 1 for formulation, and 19 for excipients^18,21. JP comprises seven similar monographs, including one for formulation and six for excipients, while CP comprises 15 similar monographs, including 2 for APIs and 13 for excipients. In contrast, the International Pharmacopoeia comprises only two monographs—both for excipients—that report microbial contamination acceptance limits^24-29. Table 1 lists the microbial contamination limits based on administration routes.

Figure 1. Graphical representation of monographs focusing on non-sterile products with microbial acceptance limits among the monographs in the Indian Pharmacopoeia.

In substances for pharmaceutical use, e.g., APIs, the limits for microbial parameters of total aerobic microbial count (TAMC) and total yeast and mould count (TYMC) are consistent across most pharmacopeias except the International Pharmacopoeia, as data are unavailable. For both aqueous preparations and non-aqueous preparations for oral use, the TAMC, TYMC, and Escherichia coli limit criteria are the same across all pharmacopeias except CP, which includes an additional criterion of absence of Salmonella.

All pharmacopeias have the same TAMC and TYMC limits for rectal use except CP, which further classifies rectal use into aqueous and non-aqueous categories with distinct limit criteria for each. The microbial limits for oromucosal, gingival, cutaneous, nasal, and auricular uses are identical in terms of TAMC, TYMC, Staphylococcus aureus, and Pseudomonas aeruginosa across pharmacopeias, with oromucosal, gingival, and nasal uses in CP involving additional E. coli detection.

The microbial limits of TAMC, TYMC, S. aureus, P. aeruginosa, and Candida albicans in vaginal use are consistent across pharmacopeias. Meanwhile, the microbial limits for urethral use in CP are the same as those specified for vaginal use, whereas corresponding data are not available in the other pharmacopeias. The microbial limits (TAMC, TYMC, S. aureus, P. aeruginosa, and sBile-Tolerant Gram-Negative Bacteria (BTGNB) are a specific group of microorganisms defined by their ability to grow in the presence of bile salts. In pharmaceutical microbiology, they are considered indicator organisms for assessing the microbial quality of products. ) for inhalation use are the same across all pharmacopeias, with CP having additional E. coli absence criteria. In the case of transdermal patches, the microbial acceptance criteria are the same across all pharmacopeias except CP, which does not have relevant data. The microbial limits for oral dispersible films are available only in Ph.Eur and BP, whereas only CP states microbial limits for other topical uses.

5. Discussion

Differences in microbial contamination acceptance limits across pharmacopeias have led to calls for greater uniformity to facilitate compliance with global markets and regulations³¹. Non-sterile pharmaceutical products are not recommended for quantifying the microbial load and assessing the bacterial load^{32, 33}. Various pharmacopeias, including IP, USP, Ph.Eur, BP, JP, CP, and the International Pharmacopeia, provide guidance on acceptance limits for microbiological contamination³⁴. These pharmacopeias adopt product-specific criteria based on factors such as the nature of the product, its potential to support microbial growth, and the quantity administered³⁵. Risk also varies according to the intended use, including the site of application (e.g., intact skin or wounds) and route of administration (e.g., ocular, nasal, or oral), as described in Chapter 2.2.9 of IP 2022.

Microbiological quality failures are occasionally detected during stability testing, highlighting the importance of risk-based approaches during manufacturing and stability analysis for establishing total microbial limits and quality control measures, as outlined in the United States Food and Drug Administration guidance, “Microbiological Quality Considerations in Non-Sterile Drug Manufacturing”⁹. Munukuntla et al.² conducted a review on differences in microbial limits and acceptance criteria for herbal drug preparations across pharmacopeias. However, technical barriers to the implementation of different pharmacopeias remain due to varying procedures for microbial enumeration, identification, and acceptance criteria. Differences in media, incubation conditions, and interpretation of results may lead to inconsistent outcomes across regions, as noted in the International Council for Harmonization of Technical Requirements for Pharmaceuticals for Human Use (ICH) Q4B guidelines³⁶. ICH is an initiative that aims to standardize criteria for microbiological quality.

In September 1989, USP, JP, and Ph.Eur established the Pharmacopoeial Discussion Group (PDG) to promote harmonization of excipient standards and testing procedures, marking an important step toward convergence³⁷. The PDG is now prepared to harmonize IP, USP, JP, and Ph.Eur to achieve greater uniformity in pharmacopeial criteria worldwide. The unified approach would facilitate global compliance, reduce regulatory complexity, and strengthen public health protection. Similarly, the annual International Meetings of World Pharmacopoeias brings together pharmacopeia organizations, regulatory authorities, and industry stakeholders to address harmonization, emerging issues, and standard development.

Despite these initiatives, progress remains slow due to limited data sharing, resource constraints, and a lack of unified governance. Harmonization aims to reduce the burden on manufacturers required to apply different analytical procedures and standards to comply with regional requirements³⁸. In addition to facilitating regulatory compliance, aligning microbiological acceptance standards would enhance patient safety and ensure microbial quality across markets. While current Good Manufacturing Practice guidelines emphasize microbial control, alignment of pharmacopeial limits would further support systematic implementation of these practices^{39, 40}. Ultimately, such harmonization could reinforce international quality standards and mitigate microbiological challenges associated with non-sterile pharmaceutical products².

6. Conclusion

This study compared the microbial limit acceptance criteria of non-sterile pharmaceutical products across different pharmacopeias, which is crucial for ensuring drug safety and effectiveness. Microbial contamination in non-sterile medicines remains an important safety concern. Current microbial acceptability limits and testing protocols show significant variability among pharmacopeias. While pharmacopeias such as USP, BP, and Ph.Eur provide important frameworks for microbial control, differences in acceptance criteria highlight the need for harmonization. A unified approach would facilitate global compliance, reduce regulatory complexity, and ultimately enhance public health protection for pharmaceutical products worldwide. Harmonization among the USP, Ph.Eur, JP, and other pharmacopeias is therefore critical to addressing global regulatory challenges, streamlining testing protocols, and improving product safety. Future efforts should focus on harmonizing pathogen-specific requirements and adopting risk-based approaches consistent with modern manufacturing practices.