In conjunction with the more expensive and lengthy in vivo animal studies, simpler in vitro test, such as cytochrome P-450 enzymes and Ames tests are increasingly being applied. P450 enzymes make up a superfamily
of hemoproteins with highly diverse functions, including drug metabolism in humans; whereas, the Ames test can be used to
determine mutagenic potential of drugs. The goal of these early development studies is to examine the drug in living systems
before going to human clinical trials.
As the drug candidate moves later into the process development phase, assays are needed to support formulation of drug product,
including ingredients and excipients. Many excipients have associated methods described in the various compendia: United States
Pharmacopoeia (USP), European Pharmacopoeia EP, British Pharmacopoeia (BP), and Japanese Pharmacopoeia (JP); while other will
need new methods developed and validated or supplied by the vendor.
Extractables and Leachables
The drug delivery system also has to be developed. Because of stability issues, biopharmaceuticals are typically not formulated
as tablets, capsules, or the other more common vehicles used for small, stable, active pharmaceutical ingredients. An area
of increasing concern and scrutiny for FDA is the potential adulteration of drug products by extractable and leachable compounds—contamination
from the container, closure system, device, etc., that comes into contact with the drug formulation.
Extractables are compounds that can be extracted from a component under exaggerated conditions such as in the presence of
harsh solvents or at elevated temperatures. These compounds have the potential to contaminate the drug product. Leachables
are compounds that leach into the drug product formulation from the component as a result of direct contact with the formulation
under normal conditions. Leachables are typically a subset of extractables. Sources of these compounds include plastic components,
elastomers, coatings, accelerants, antioxidants, inks, and vulcanizing agents. Phthalates are one specific example.
These potential carcinogens are added to plastics to make them more flexible and can be found throughout the manufacturing
process, as well as in packaging materials. Other examples are nitrosamines and polynuclear hydrocarbons (PAHs) which are
classes of carcinogenic compounds found in rubber. Many drug products are distributed or administered in packages made of
plastic and rubber components, and therefore, phthalates, PAHs, and nitrosamines could potentially come into contact with
the drug product and be passed on to the patient.
Evaluation of extractables and leachables can be an arduous task. Studies must be properly designed, and a wide array of potential
contaminants must be screened for using approaches like those described in Table 2.
Table 2. Testing must be conducted to identify extractables and leachables that may contaminate the drug product.
Extractables and leachables issues should be addressed early in the process to avoid regulatory delays for the drug manufacturer.
The development of unique packaging and delivery systems required for biopharmaceuticals has intensified this issue due to
the growing possibilities of "foreign" materials coming into contact with drug products.
Material will initially be produced on the laboratory scale. As more material is needed for clinical trials, the manufacturing
moves to pilot scale. Successful drugs will then progress to a large-scale commercial production environment, and all aspects
of this environment must be validated, including water, air, and cleanliness of equipment.
GMP regulations require the testing of water for injection (WFI) and purified water (PW). An example of the battery of test
performed is shown in Table 3.
Table 3. GMP regulations require testing of water for injection (WFI) for common contaminants.