As discussed, an early preformulation decision is whether the final formulation will be liquid or lyophilized, a choice that
determines which excipients will be needed. (Liquid and lyophilized products require different excipients.) Some industry
experts advocate developing both types of formulation in parallel. In concert with all these steps, a placebo formulation
containing all but the active ingredient also must be developed for use in blinded clinical trials.
The package. Four important preformulation stress tests are the shake test (agitation), surfactant test, freeze-thaw test, and heating
experiments. Each formulation configuration is shaken in a vial to determine whether it forms aggregates. Then a surfactant
(usually a polysorbate detergent such as Tween) may be selected to prevent formation of precipitants by making it harder for
proteins to aggregate. Formulations are checked through multiple freeze-thaw cycles (which can take about a week) to check
for the effects of temperature and freezing-process stresses. Most proteins are stable around 2-8°C, but few are stable at
room temperature. Heating experiments help scientists examine degradation at temperature extremes by heating them to 30°C
(about 86°F), and maybe even 45°C (about 113°F). At high temperatures, different mechanisms of protein denaturation may arise.
(For more information on what can go wrong, see the next chapter.)
Formulators cannot ignore any potential interactions, which means paying attention to container materials. Is the formulation
compatible with the vessel and closure? Some proteins may stick (adsorb) to the walls of a vial or other container, particularly
in low-concentration formulations. Glass is reactive; it can be delaminated, for example, through contact with a formulation.
Certain kinds of plastic may be less reactive than glass.
Will the formulation react with the stopper or elastomer? Such contact could destroy the protein. Stopper materials are selected
based on their reactivity with the formulation. To test for that, vials are inverted — to give their rubber stoppers total
contact with the formulation — and then stored horizontally to create more surface area — and more chances for the protein
to degrade. More oxidation of the protein can occur as the surface area grows larger.
The filling process (discussed in the final chapter of this guide) should remove as much oxygen as possible from a vial's
headspace because oxygen can cause a certain kind of degradation. Potential product extractables and packaging leachates must
be listed in regulatory submissions. Preformulation development may take three to six months or more, depending on the instability
and reactivity of the active bulk substance with its excipients. Interrelated preformulation activities may determine whether
a molecule can be developed into a marketable drug.
Know Your Molecule
Development of any protein formulation should be done empirically, considering the final dosage configuration, because of
the enormous potential for interaction between the ingredients, the packaging or delivery device, and even the patient's body
itself (for example, at the site of injection or delivery). Protein molecules interact with other molecules following their
own rules and tendencies. They have had billions of years of evolution to reach this state of complexity, and we have had
only a couple of centuries to learn about them.
"Characterization is . . . about knowledge and intimate understanding of your biopharmaceutical and any product- or process-related
impurities," notes biopharmaceutical analytical scientist Jim Faulkner. "Ultimately, characterization is about deciding what
features of your molecule need to be under control and what features are noncritical to its overall quality. Ideally, that
information would be in hand at the beginning of the product development program. Clearly, that is unrealistic. Therefore,
product characterization is an evolving process that involves contributions at different stages of the product life cycle.
Assuming that characterization is purely a development exercise is wrong; the moment a biotherapeutic is identified for development,
the process of characterization has begun."
The new biologics regulatory paradigm in place since the late 1990s refers to biopharmaceuticals as "well-characterized biologics."
But to take advantage of the lessened restrictions for certain products overseen by FDA's Center for Biologics Evaluation
and Research (CBER), companies must prove that their products are indeed well characterized.
Meanwhile . . . Documenting the Work
As a product moves through production, purification, formulation, and fill and finish, the quality control (QC) department
tracks every process component from the point of purchase or in-house development. QC ensures the safety of development scientists
and patients. As soon as a company moves its formulation from research and development (R&D) into development and manufacturing,
QC starts designing systems for documenting the company's compliance with good manufacturing practices (GMPs) for FDA.
|
