Quality Assurance of Pharmaceuticals - A Compendium of Guidelines and Related Materials - Volume 1
(1997; 248 pages) [French] View the PDF document
Table of Contents
Open this folder and view contentsIntroduction
Open this folder and view contents1. National drug regulation
Open this folder and view contents2. Product assessment and registration
Open this folder and view contents3. Distribution
Close this folder4. The international pharmacopoeia and related activities
View the documentGuidance for those preparing or commenting on monographs for preparations to be included in The international pharmacopoeia1
View the documentValidation of analytical procedures used in the examination of pharmaceutical materials1
Open this folder and view contentsGeneral guidelines for the establishment, maintenance, and distribution of chemical reference substances1
View the documentGeneral recommendations for the preparation and use of infrared spectra in pharmaceutical analysis1
View the documentList of available International Chemical Reference Substances1
View the documentList of available International Infrared Reference Spectra1
Open this folder and view contents5. Basic tests
Open this folder and view contents6. Laboratory services
Open this folder and view contents7. International trade in pharmaceuticals
Open this folder and view contents8. Counterfeit products
Open this folder and view contents9. Training
View the documentSelected WHO publications of related interest
View the documentBack cover
 

Validation of analytical procedures used in the examination of pharmaceutical materials1

1WHO Expert Committee on Specifications for Pharmaceutical Preparations. Thirty-second Report. Geneva, World Health Organization, 1992 (WHO Technical Report Series, No. 823).

1. What is analytical validation?

Analytical monitoring of a pharmaceutical product, or of specific ingredients within the product, is necessary to ensure its safety and efficacy throughout all phases of its shelf-life, including storage, distribution, and use. Ideally, this monitoring should be conducted in accordance with specifications elaborated and validated during product development. This ensures that the quality specifications are applicable to the pharmaceutical material used to establish the biological characteristics of the active substances as well as to the marketed dosage forms. When the biomedical evaluation of the product is completed, the acceptability of all subsequent batches will be judged solely on the basis of these specifications.

The principal purpose of analytical validation is to ensure that a selected analytical procedure will give reproducible and reliable results that are adequate for the intended purpose. It is thus necessary to define properly both the conditions in which the procedure is to be used and the purpose for which it is intended. These principles apply to all procedures described in a pharmacopoeia and to non-pharmacopoeial procedures used in a manufacturing company.

These guidelines apply to procedures used to examine chemical and physico-chemical attributes, but many are equally applicable to microbiological and biological procedures.

2. Presentation of data on analytical procedures for product registration or pharmacopoeial monographs

Any data on analytical procedures presented in support of a specification proposed for a particular ingredient (drug substance or excipient) or dosage form should be provided under three main headings:

1. Justification for the proposed test procedure in comparison with other possible approaches. Where an unusual procedure is proposed, its scientific basis should also be discussed. Where the procedure is being proposed to replace an existing one, comparative data should be provided.

2. Description of a procedure giving as much detail as is deemed necessary to allow properly trained workers carry it out in a reliable manner. The reagents required should be defined (either in detail or by reference to readily available published texts) and details concerning the availability of any reference substances required should be given. Where the procedure is based on the application of well established principles of analytical chemistry, it should not be necessary to provide formulae for the calculation of results. Where, however, the method is complex, a full formula for the calculation of results should be included, with all terms defined.

3. Validation data. Each analytical performance characteristic that is applicable to the particular procedure defined (see section 4) should be discussed and supported by experimental data. Where the data presented for registration purposes rely on established pharmacopoeial methods, the need for supporting validation data may be considerably reduced, on the assumption that the pharmacopoeial procedures have already been properly validated. However, evidence that the pharmacopoeial procedure is applicable to the material under test may well be required, especially for dosage forms.

3. Characteristics of analytical procedures

The characteristics that may need to be specified for analytical procedures are listed below and defined (for the purposes of this text), with an indication of how they may be determined.

Not all the characteristics are applicable to every test procedure or to every material. Much depends on the purpose for which the procedure is required. This aspect of validation is discussed in section 4.

Accuracy

The accuracy of the procedure is the closeness of the results obtained by the procedure to the true value. Accuracy may be determined by applying the procedure to samples of the material to be examined that have been prepared with quantitative accuracy. Wherever possible, these samples should contain all the components of the material, including the analyte. Samples in which the analyte has been incorporated in quantities some 10% above and below the expected range of values should also be prepared. Accuracy may also be determined by comparing the results with those obtained using an alternative procedure that has already been validated.

Precision

The precision of the procedure is the degree of agreement among individual test results. It is measured by the scatter of individual results from the mean and it is usually expressed as the standard deviation or as the coefficient of variation (relative standard deviation) when the complete procedure is applied repeatedly to separate, identical samples drawn from the same homogeneous batch of material.

Repeatability (within-laboratory variation)

This is the precision of the procedure when repeated by the same analyst under the same set of conditions (same reagents, equipment, settings, and laboratory) and within a short interval of time. The repeatability of a procedure is assessed by carrying out complete, separate determinations on separate, identical samples of the same homogeneous batch of material and thus provides a measure of the precision of the procedure under normal operating conditions.

Reproducibility

This is the precision of the procedure when it is carried out under different conditions - usually in different laboratories - on separate, putatively identical samples taken from the same homogeneous batch of material. Comparisons of results obtained by different analysts, by the use of different equipment, or by carrying out the analysis at different times can also provide valuable information.

Robustness

Robustness, or ruggedness, is the ability of the procedure to provide analytical results of acceptable accuracy and precision under a variety of conditions. It is a measure of the extent to which the results obtained from separate, putatively identical samples of the same homogeneous batch of material are influenced by changes in operational or environmental conditions but are consonant with the specifications laid down for the procedure.

Linearity and range

The linearity of an analytical procedure is its ability to produce results that are directly proportional to the concentration of analyte in the samples. The range of the procedure is an expression of the lowest and highest levels of analyte that have been demonstrated to be determinable with acceptable precision, accuracy, and linearity. These characteristics are determined by application of the procedure to a series of samples having analyte concentrations spanning the claimed range of the procedure. When the relationship between response and concentration is not linear, standardization may be provided by means of a calibration curve.

Selectivity

The selectivity or specificity of a procedure is its ability to measure the analyte in a manner that is free from interference from other components in the sample being examined (for example, impurities arising from manufacture or degradation or ingredients other than the analyte, whether these are pharmacologically active or inert). Selectivity (or lack of it) may be expressed in terms of the bias of the assay results obtained when the procedure is applied to the analyte in the presence of expected levels of other components, compared to the results obtained on the same analyte without added substances. When the other components are all known and available, selectivity may be determined by comparing the test results obtained on the analyte with and without the addition of the potentially interfering materials. When such components are either unidentified or unavailable, a measure of selectivity can often be obtained by determining the recovery of a standard addition of pure analyte to a material containing a constant level of the other components.

Sensitivity

Sensitivity is the capacity of the test procedure to record small variations in concentration. It is the slope of the calibration curve. A more general use of the term to encompass limit of detection and/or limit of quantitation should be avoided.

Limit of detection

The limit of detection is the lowest level of analyte that can be detected, but not necessarily determined in a quantitative fashion, using a specific method under the required experimental conditions. Such a limit is usually expressed in terms of a concentration of analyte (for example, in micrograms per litre) in the sample. Where the final measurement is based on an instrumental reading, due account will need to be taken of the background response (the signal-to-noise characteristics of the responses observed).

Limit of quantitation

The limit of quantitation is the lowest concentration of analyte in a sample that may be determined with acceptable accuracy and precision when the required procedure is applied. It is measured by analysing samples containing diminishing known quantities of the analyte and determining the lowest level at which acceptable degrees of accuracy and precision are attainable. Where the final assessment is based on an instrumental reading, the magnitude of background response (the signal-to-noise ratio) may need to be assessed and taken into account. In many cases the limit of quantitation is approximately twice the limit of detection.

4. What analytical characteristics are applicable in particular cases?

Not all of the characteristics referred to in section 3 will need to be considered in all cases; those applicable should be identified on a case-by-case basis. As a guide, however, the following generalizations may assist.

Methods used for the examination of pharmaceutical materials may be broadly classified as follows:

• Class A: Tests designed to establish identity, whether of bulk drug substances or of a particular ingredient in a finished dosage form.

• Class B: Methods designed to detect and quantitate impurities in a bulk drug substance or finished dosage form.

• Class C: Methods used to determine quantitatively the concentration of a bulk drug substance or of a major ingredient in a finished dosage form.

• Class D: Methods used to assess the characteristics of finished dosage forms, such as dissolution profiles and content uniformity.

Table 1 offers guidelines to the characteristics that are relevant in each case. Notwithstanding these generalizations, there will clearly be occasions when certain characteristics marked as not being required may be necessary and vice versa. In addition, the purpose for which the submission is being made may have a bearing on the choice of characteristics and the extent to which they are specified. For example, although Classes B, C, and D are all referred to in Table 1 as requiring consideration of precision, the stringency applied may be different. For estimation of an impurity it may not be necessary to be as precise as for quantitative assessment of a bulk drug substance. By the same token, a degree of bias may be acceptable in determining the accuracy of a test for uniformity of content (Class D) that would not be permissible for a quantitative assessment of the concentration of an ingredient in a finished dosage form (Class C). Similarly, a test designed to establish the identity of a new drug entity for which no previous data have been lodged may need to be considerably more searching than tests designed to verify the identity of a long-established drug substance to be included in a pharmacopoeia.

Table 1. Characteristics that should be considered for different types of analytical procedure

 

Class A

Class B

Class C

Class D

   

Quantitative tests

Limit tests

   

Accuracy

 

×

 

×

×a

Precision

 

×

 

×

×

Robustness

×

×

×

×

×

Linearity and range

 

×

 

×

×

Selectivity

×

×

×

×

×

Limit of detection

×

 

×

   

Limit of quantitation

 

×

     

a A degree of bias may be allowed.

A different emphasis may be required for pharmacopoeial as opposed to registration purposes. For example, robustness is a critical characteristic for pharmacopoeial methodology but may be less significant for a manufacturer’s release specification.

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