Use of In-house Reference Standards Beyond Pharmacopoeial Standards

Introduction to Primary Standards (Reference Standard)

A primary reference standard in the context of pharmaceuticals is a standard whose characteristics (often identity, but frequently also purity/assay values) have been described by specific analytical procedures, but without being compared to any other standard of the same sort.

A substance that has been shown by an extensive set of analytical tests to be authentic material that should be of high purity. This standard can be: 

1. Obtained from an officially recognized source, 
2. Prepared by independent synthesis, 
3. Obtained from existing production material of high purity, 
4. Prepared by further purification of existing production material.

• The US Food and Drug Administration (FDA) or a company or laboratory indicates primary standard material as a highly purified compound that is well characterized; the quality and purity of primary standards are very important in determining scientifically reasonable results for analytical methods in the pharmaceutical industry.

• Purity, quality, and potency are identified in the pharmaceutical industry using active pharmaceutical ingredients (APIs) and medicinal products about their quality primary standards.
• Quantitative data (like assay and impurity), qualitative data (like identification test), and calibration data (like melting point standard) are all determined using primary standards. Therefore, obtaining results that are scientifically legitimate depends greatly on the quality and purity of the primary standards.

A reference standard is a highly purified and well-characterized material suitable to test the identity, strength, quality, and purity of substances for Chemical, pharmaceutical, and medicinal products. Using reference standards, working standards can be prepared. Reference Standards can be taken from USP, EP, BP, and IP or In-house.

Types of Reference Standards

In the pharmaceutical, there are five major types of reference standards:

1. Primary RS
2. Pharmacopoeial RS (for monograph use)
3. Secondary RS
4. Impurity RS
5. Research Materials

• Apart from the pharmacopoeial standards, all of the above come with certificates of analysis (CoAs), or – in the case of secondary RSs – with a comparison statement. The information provided on the CoA should be suitable with regard to the specific use planned for the corresponding RS.
• Research Materials – which is often used at the very beginning of analytical research and development, but not normally for method development, validation, transfer or quality control. 
• The reference standards are used as the basis for quantitative and qualitative testing.
• Impurity Reference standards: The reference standards used in the analytical procedures to control impurities should be evaluated and characterized according to their intended uses.

ALSO READ: SOP for Reference Standard Control

Limitations of Pharmacopoeial Primary Standards

• Relying solely on Pharmacopoeial primary standards for ensuring the quality and efficacy of pharmaceutical products has limitations due to variations in equipment, analytical methods, and sample matrices. Equipment variations in calibration, sensitivity, precision, and accuracy can lead to discrepancies in measured values. 
• Analytical method variations in sample preparation, reagent quality, temperature control, extraction methods, and detection techniques can affect results. Complex sample matrices with excipients, impurities, and degradation products can interfere with accurate measurements. 
• The limited availability of suitable primary standards and reference materials introduces uncertainties. To address these limitations, robust quality control systems are established, incorporating method validation, equipment qualification, and reference material characterization. 
• Collaborative efforts among regulatory bodies, industry stakeholders, and standards organizations aim to develop and harmonize standards, promoting consistency and reliability in pharmaceutical analyses.

What are In-house Primary Standards?

• The term "in-house primary standard" refers to a primary standard that is developed and synthesized by a particular organization or industry, rather than by the official pharmacopoeial regulatory body.
• A primary reference standard is a highly purified substance with well-defined properties and established purity, used as a benchmark for comparison and quality control in the analysis of pharmaceuticals. These standards serve as a reference point against which the quality and characteristics of drug substances or drug products can be measured.

• While the pharmacopoeial regulatory bodies are responsible for establishing and maintaining official standards for pharmaceuticals, including primary reference standards, it is possible for industries or organizations to develop their own in-house primary reference standards. These in-house standards can be synthesized and validated according to established protocols and procedures, ensuring their accuracy and reliability.
• The use of in-house primary reference standards allows industries to have direct control over the quality and consistency of the substances they produce. However, it is important to note that these in-house standards may not be recognized or accepted universally, as they are not established by the official pharmacopoeial regulatory body. Therefore, when assessing the quality of pharmaceuticals, the acceptance and recognition of in-house primary reference standards may vary depending on the specific regulatory requirements and guidelines in different regions or countries.

The Emergence of In-house Primary Standards

The benefits of establishing in-house primary standards are significant:

1. Customization: In-house primary standards can be designed to closely align with the company's specific measurement needs. This allows for more precise calibration and validation of instruments used in the company's operations, leading to improved accuracy and reliability in measurements.
2. Cost-effectiveness: While acquiring primary standards from external sources may be expensive, acquiring in-house standards can be more cost-effective in the long run. It eliminates the need to rely solely on external providers, reduces costs associated with outsourcing calibration services, and minimizes potential downtime due to delays in obtaining external standards.

ALSO READ: SOP for Preparation of Data Sheets for Working Standard

Advantages of In-house Primary Standards in Pharmaceutical

Utilizing In-house primary standards has many benefits for the pharmaceutical sector. The following are some of the most significant benefits:

1. Enhanced precision and accuracy:

• In-house primary standards are typically more precise and accurate than secondary reference standards. This is because they are prepared under controlled conditions and are not subject to the same variability as secondary reference standards.

2. Customized to fit special requirements:

• In-house primary standards can be tailored to meet the specific requirements of a particular product or process. This can be important for ensuring the quality and consistency of products.

3. Efficiency and cost-effectiveness:

• In-house primary standards can save time and money by eliminating the need to purchase pharmacopoeial standards.

When a pharmacopeial reference standard is not available, then it is prepared by synthesizing as per below:

• If a pharmacopeial reference standard is not available, it can be prepared by synthesizing a reference material from a particular batch. The batch number should be assigned to the reference material, and its characteristic properties should be documented for reference purposes and comparison with future production lots. The material selected as a primary standard should be highly stable, free from water or hydration, and traceable to a national or international standards body.
• The batch-specific certificate of analysis will also include details on the recommended storage conditions, as well as sample spectra and chromatograms.
• The conditions of storage for reference standards and impurity standards need to be carefully considered. They should be stored at room temperature, and protected from light, moisture, freezing, and excessive heat. They should also be stored in clean vials or suitable vials for storage. 

Here are some additional details about the preparation and storage of pharmacopeial reference standards:

1. The selection of reference material is critical to the quality of the final product. The material should be highly pure and free from impurities.
2. The synthesis of the reference material should be carried out in a clean environment using validated methods.
3. The reference material should be stored in a cool, dry place in a tightly sealed container.
4. The reference material should be regularly checked for stability and purity.

By following these guidelines, you can ensure that your pharmacopeial reference standards are of the highest quality.

Can we use the Primary Standards from other sources apart from Pharmacopeia?

• Yes, it is possible to use primary standards from regulatory sources other than pharmacopeia. Primary standards are highly pure reference substances that have well-defined properties.
• When using primary standards from regulatory sources other than pharmacopeia, it is important to ensure that they are appropriate for the intended purpose and meet the necessary quality and regulatory requirements. The selection and use of primary standards should be based on a thorough understanding of the specific regulatory guidelines and requirements relevant to your particular industry and region.

ICH guideline Q7 states:

• Primary reference standards should be obtained as appropriate for the manufacture of APIs. The source of each primary reference standard should be documented. Records should be maintained of each primary reference standard’s storage and use in accordance with the supplier’s recommendations. 
• Primary reference standards obtained from an officially recognized source are normally used without testing if stored under conditions consistent with the supplier’s recommendations. Officially recognized sources, however, are not specified in ICH Q7.

ALSO READ: Contamination and Cross-Contamination in Pharmaceutical Manufacturing

FDA states:

• The FDA does mention sources in their Guidance for Industry on Analytical Procedures and Methods Validation for Drugs and Biologics. Reference standards can often be obtained from the USP and may also be available through the European Pharmacopoeia, Japanese Pharmacopoeia, World Health Organization, or National Institute of Standards and Technology.
• Instead, the FDA states that “reference materials from other sources should be characterized by procedures including routine and beyond routine release testing” and that producers “should consider orthogonal methods for reference material characterization”.

This approach reads differently, but is exactly in line with the definition for primary RSs in ICH Q7, discussed above. For primary RSs, both the ICH guideline and FDA guidance allow other sources than the “officially recognized sources”. Independent manufacturers can provide such primary standards, ideally characterized by processes like those outlined in the general text 5.12. of the European Pharmacopoeia (Ph.Eur).

Reference Standard Can prepare as per the below procedure:

• Highest purity grade material with completely characterized materials
• Reliable chromatographic methods for purity determination.
• Residual solvent impurities include organic, inorganic, and an aqueous solvent.
• Validated methods used to confirm the consistent and precise results
• Qualified instruments are used for the qualification of the reference standard.

Reference Standard identity and purity standards:

As a part of the qualification of identity and purity standards, minimal required tests for initial characterization were typically performed by using the following tests:

1. Purity & structure confirmation by 1H- NMR and 13C- NMR spectroscopy,
2. Recording of coupled spectra as required Mass spectroscopy
3. Metals impurity by inductively coupled plasma mass spectrometry (ICP-MS)
4. Identification & structure confirmation by UV and/or IR spectroscopy
5. Chromatographic purity by using HPLC
6. Residual solvents by Headspace gas chromatography (HSGC-FID)
7. Water content by Karl Fischer titration or Thermogravimetric analysis.
8. Non-combustible impurities by residue on ignition/sulfated ash test

Essentials of Secondary Standards

• Secondary reference standards are, as the name suggests, second-line materials. They consist of each instance of a material that is compared against the primary material and used instead of that.
• It does not matter whether the secondary standard is compared against a pharmacopoeial primary standard, or against a primary standard obtained in-house or from a third source. Of particular note, a secondary standard can only be used for the same purposes as the primary standard. Thus if a primary standard was designed solely for a qualitative purpose (i.e. identification via IR, system suitability test or peak identification), then using the corresponding secondary standard for quantitative purposes is not valid. 
• For example: a large number of Ph.Eur. reference standards for APIs have been set up for IR comparisons only, and should not be used as a basis for quantitative secondary standards.
• In addition, the EDQM (European Directorate for the Quality of Medicines) does not recommend measuring secondary standards against even their quantitative materials. This is because:

1. While pharmacopoeial primary RSs have a determined measurement uncertainty (MU) in line with the requirements of the relevant pharmacopoeial monograph, the value of this uncertainty is not currently specified.
2. The comparison of candidate material for a secondary RS to the pharmacopoeial RS will result - by the principle of uncertainty propagation – in a larger but non-quantifiable MU for the secondary standard, by virtue of the fact that the MU for the Pharmacopoeial material is not published
3. This unknown but enlarged MU for the secondary RS might no longer be appropriate for the acceptance interval specified in the relevant monograph.

For the same reason, the use of a Pharmacopoeial RS with a non-compendial method can be difficult to justify on the basis that the uncertainty of its value assignment is unknown.

ALSO READ: Skip Testing in Pharmaceutical Industry: Where to Apply?