Quantitative Methods—Validation Considerations

Validation of quantitative leachables methods should be accomplished according to industry accepted practices, criteria, and standards, such as Validation of Compendial Procedures 1225 and (11). The extent of validation required depends on the goals of the leachables study in which the analytical method is being utilized. Validation parameters may include: accuracy, precision (repeatability, intermediate precision), specificity, limit-of-detection, limit-of-quantitation, linearity and range, and robustness. System suitability tests and criteria should also be developed for each leachables method. Special considerations for individual validation parameters relative to leachables methods are as follows:

  • Accuracy and precision—The validation parameters of accuracy and precision (repeatability and intermediate precision) are typically evaluated using drug product samples spiked with known amounts of target leachables. The choice of drug product spiking matrix used for these evaluations should be one that has had little-to-no contact with the packaging materials used in the final drug product, and therefore little-to-no measurable levels of endogenous leachables. Suitable spiking matrices can include freshly manufactured drug product and simulated drug product vehicles. Spiking levels should be determined based on results from accelerated stability studies or estimated from the known amounts of potential target leachables determined from extraction studies. Accuracy is typically performed at three spiking levels, which can also be determined based on results from accelerated stability studies or estimated from the known amounts of potential target leachables determined from extraction studies.

  • Linearity and range—Since potential leachables are present in packaging components at widely varying levels, actual drug product leachables can likewise appear at widely varying levels. The best accuracy and precision are achieved when the validated linear range considers the potential maximum accumulation levels of each target leachable or chemical class of leachables.

  • Limit of detection/Limit of quantitation—To detect and quantitate unknown leachables, the limit of quantitation should be at or below the designated analytical threshold (e.g., AET).

  • Specificity—Evaluation of method specificity can be accomplished by evaluating chromatographic peak purity in spiked and nonspiked drug product samples. For GC-based quantitative methods, this can be accomplished by GC/MS. For HPLC-based methods, either LC/MS or LC/DAD (diode array detection) can be used. Specificity can be qualitatively demonstrated if there are no observable method interferences related to the chemical entities present in the drug product.

  • Robustness—A design-of-experiments statistical approach with consideration of critical analytical method parameters (e.g., HPLC flow-rate, HPLC column, mobile phase gradient, etc.) should be used to create robustness evaluation protocols. Other approaches, such as serial change of critical parameters, can also be applied.

Several examples of validated leachables methods from the scientific literature have been documented in the chemical literature (12–17).


A leachables–extractables correlation is established when actual drug product leachables can be linked either qualitatively or quantitatively with extractables from corresponding extractables assessments of individual materials of construction, packaging components, or packing systems. Leachables–extractables correlations are important for several reasons, including justifying the use of routine extractables release tests of packaging components as an alternative to leachables testing during stability studies for high-risk drug products, establishing the source of a leachable producing an OOS result for a low-risk drug product, change control, and ongoing quality control, etc.

A qualitative correlation is demonstrated when a leachable is linked either directly or indirectly to an extractable (i.e., potential leachable). For example, hexadecanoic acid observed in a leachables profile can be directly linked with hexadecanoic acid observed in the extractables profiles of one or more primary packaging components. The ethyl ester of hexadecanoic acid observed in the same leachables profile can be indirectly linked with hexadecanoic acid observed in one or more extractables profiles, if ethanol is a known drug product formulation constituent and it is shown that an esterification reaction can occur in the drug product during storage. For an appropriate quantitative leachables–extractables correlation to exist, the quantity of any individual leachable over the shelf-life of a drug product must be mathematically related to the quantity of the corresponding extractable in its source. 

One of the more simple mathematical relationships between an extractable and a leachable is that the quantity of the leachable in the drug product should be less than or equal to the quantity of the corresponding extractable. For example, the concentration of butylatedhydroxytoluene (BHT) present in a drug product formulation was determined to be 5 µg/mL. BHT was extracted from a primary packaging system component at a level of 300 µg/component. If the drug product packaging system incorporates one of these components per dosage form and the packaged formulation has a volume of 50 mL, then a quantitative leachables–extractables correlation is established, as BHT was extracted in the amount of 300 µg (300 µg/component × 1 component) and was leached in the amount of 250 µg (5 µg/mL × 50 mL). As a result, it can be concluded that on the average 50 µg of BHT is unaccounted for (300 µg extracted 250 µg leached), and that this quantity was either not leached from the packaging component into the formulation (more likely) or lost by some other process (less likely).

For high-risk drug products, leachables–extractables correlations may be established over multiple batches of drug product (accelerated or at end of shelf-life) and multiple batches of packaging components. Extractables studies should ideally be conducted on the same lots of components that were used to manufacture the drug product batches used in primary stability studies (and therefore on the drug product batches on which leachables testing was conducted to establish leachables–extractables correlations).

If the maximum level of any specific leachable in the formulation during stability studies was substantially greater than the calculated maximum potential accumulation levels of that same leachable as established by the extraction study, and the extraction studies were conducted on the same lots of components used to make the primary drug product stability batches, it can be concluded that the extraction study was incomplete and therefore a leachables–extractables correlation for that specific leachable cannot be established. In this case, either the extraction study can be augmented with experiments that produce an extractable level exceeding the maximum level of the leachable, or the leachable can be controlled via the drug product specifications for shelf-life stability testing, and release testing as an extractable at the component level is inadequate to control this leachable.

If a leachable–extractables correlation cannot be established, possible explanations include: inadequate extractables assessments of packaging components (see 1663); unreported changes in packaging component composition or manufacturing processes; unreported changes in the identity of packaging components.




The validated analytical methods and information obtained from those methods in a drug product leachables study can be used to develop drug product leachables specifications and acceptance criteria (i.e., limits). In certain circumstances, most commonly encountered with high-risk dosage forms (such as OINDP), it may be meaningful, useful, and at times required to routinely monitor finished drug products for leachables. Under such circumstances, leachables specifications and acceptance criteria must be established. 

One means by which such specifications and acceptance criteria could be developed includes testing a minimum of three drug product batches to determine their leachables levels. After thorough chemical and safety evaluation, the test data from the three or more batches can be used to establish acceptance criteria for targeted leachables, consistent with 1) the qualitative and/or quantitative results of leachables studies, 2) a consideration of the capabilities of the drug product's manufacturing process, and 3) a consideration of the potential safety, compatibility, and/or drug product quality impact of the leachables. It is important to note that leachables specifications should be applicable to a product during all stages of its shelf-life, including release and at end of shelf-life. This is the case since leachables accumulate over the entire shelf-life of a drug product.


When a change occurs in a product for which leachables specifications and acceptance criteria have been established, it is important to review the analytical method and re-evaluate the acceptance criteria and make adjustments to the specifications and acceptance criteria as appropriate and scientifically justified. A change in components that results in an increase in leachables concentrations beyond the levels qualified will necessitate the toxicological evaluation of the proposed levels, as would be the case for any impurity.


Acceptance criteria can be both qualitative and quantitative for both known and unspecified leachables. For example, a typical leachables specification could include: