Composite assay

The assay of potency involves the determination of the API to ensure conformance to label claim. For tablets or capsules, a composite assay requires fO-20 units to minimize tablet-to-tablet variation. In assays, it is critical for the quantitative extraction and recovery of the API meet the typical specification limit between 90.0% and 110.0% of label claim. 

TABLE 2 Composite Assay Data of Controlled-release Tablets Using Various Solidhandling and Extraction Techniques... 

Key performance requirements for composite assay methods are provided in ICH guidelines Q2A, Q2B, Q3A and Q3B. ICH Guidelines are discussed further in Chapter 10. To summarize briefly, and with some generalizations, HPLC methods applicable to the analysis of DS synthesized via the commercial route and final formulations of DP, should meet the following criteria ... 

Potency (composite assay) plan 2 with few locations... 

Potency can also be evaluated during validation. It is assumed that some number of composite assays are tested during validation. One criterion might be to generate a 100(1 - a)% confidence interval about the mean using all the potencies collected. This interval will contain the true batch potency with 100(1 - a)% confidence. This interval should be contained within the potency in-house or release limits. Enough potencies should be looked at to have sufficient power that this interval will be contained within the desired limits. 

Meeting the foregoing criterion should not be interpreted to mean that an individual composite potency assay will meet the in-house limits with high assurance. If this is desired, a prediction interval for a single future observation, or better yet, a tolerance interval, should be used. The validation specialist should be cautioned that additional composite assays might need to be tested to meet either one of these criteria with high confidence. 

At a minimum, each of the composite assay results obtained should fall within the desired limits, either the potency shelf specifications or the potency in-house (or release) limits. The in-house limits are felt to be the more appropriate, since these are the limits that ensure that the product will meet the shelf limits throughout expiry. 

As an example of the development of automated sample preparation procedures. Shamrock et have described a procedure for automating a validated manual method for Roxifiban (fibrogen receptor antagonist) tablet composite assay. Automated analyses are performed using a Zymark tablet processing workstation II (TPWII) in a 10-step format, as follows ... 

Figure 6.11. An example of a composite assay (combining both assay and impurity testing in one method) for a drug substance in early development. Note that the absorbance of the API must be <1.5 absorbance units (AU) to prevent detector saturation. Since the method has some deficiencies (e.g., partial resolution between several peaks), an improved gradient method was thus developed (Chapter 8).

Composite Assay Method for a Neutral Drug Substance... 

Table 9.9. Validation Results of a Composite Assay Method (Assay and Impurity) of a Drug Substance...

Oxidation product (amount and composition) assay techniques... 

Fig. 20.22 Plots of Af (obtained from EQCM) vs. Q (obtained from coulometry) for the compositional assay of polypyrrole-platinum composites. The analytical results are contained in Table 20.5. (Reproduced with permission from Ref. 83.)...

Fig. 5. (Left) HPLC trace of a mixture of standards used for the base composition assay 1 = dC. 2 = dU. 3 = 1,4 = dl, 5 = dG, 6 = T, 7 = dA (Right) HPLC trace of a typical mixture obtained from digestion of a representative oligonucleoside phosphorothioate sample. The peak identities are referred to by the aforementioned numbers these peaks accounted for ca. 99% of the total integrated signal intensity.

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