by Giuliana Miglierini
Formulation is a critical step in the development of new medicinal products, as it directly influences the bioavailability, release profile and stability of the active ingredient, overall impacting on both the efficacy and safety of the medicine.
While in the traditional approach the definition of the final formulation was a quite late step along the development process, new models of R&D greatly focus on early formulation as a way to optimise both time and costs of drug development. It is thus important to identify the optimal formulation strategy as early as possible: a quite challenging goal in many instances, especially in the case of last generation complex biopharmaceuticals which may prove difficult to formulate. An article by Felicity Thomas, published in Pharmaceutical Technology discusses how to address early formulation strategies to maximise the chance of success.
Limits and challenges of formulation
The main objective of the drug development process remains the same, reducing as much as possible the time-to-market so to fully exploit the marketing exclusivity period granted by the patents protecting an innovative medicine.
To this instance, some key aspects should be considered in order to rapidly establish the most appropriate formulation, with a special attention to achieving an early access to first-in-human assessment and proof-of-concept studies.
Scaling-up of the formulation process is another critical issue, as it requires a careful consideration of all the steps needed to establish the final manufacturing process at the commercial scale. This exercise is fundamental in order establish the critical quality attributes and process parameters, thus reducing the risk of a change of the initial formulation to make it suitable to the final manufacturing process.
As explained by Jessica Mueller-Albers, strategic marketing director Oral Drug Delivery Solutions, Evonik, the increased pressure to speed up formulation is also connected to the fact “many new drugs target small therapeutic areas, where it is essential for pharma companies to be first in the market from an economic perspective.”
The availability of enabling technologies is fundamental to early formulate niche medicinal products, moving away from the classical mass production. The trend initiated with the development of mRNA Covid-19 vaccines may represent a change of paradigm in drug development, suggests Jessica Mueller-Albers. Lipid nanoparticles (LNPs) are an example of enabling technology that has been widely employed to formulate the mRNAs used in Covid-19 vaccines. LNPs may take many different forms, i.e. liposomes, lipoplexes, solid lipid nanoparticles, nanostructured lipid nanoparticles, microemulsions, and nanoemulsions (see more in Drug Development and Delivery).
Other types of emerging technologies are also widely investigated, such as proteolysis-targeting chimeras (PROTACS). These are heterobifunctional nanomolecules, containing one moiety recognised by the E3 ligase and chemically linked to a ligand (small molecule or protein) able to bond to the target protein. The final outcome is the formation of a trimeric complex, through which it becomes possible to transfer ubiquitin molecules to the target protein. The mechanism represents an alternative approach to “knock down”, as it enables the degradation of the target protein, offering many advantages compared to the use of classical inhibitors.
Another challenge to be faced during formulation development is the need of a broad and specialised expertise in the different domain of drug development, including also material characterisation, drug metabolism and pharmacokinetics. According to Stephen Tindal, director, Science & Technology, Europe, Catalent, this is particularly true for small companies, which are often the focus of early development activities before acquisition of the projects by larger multinationals. As explained in the Pharmaceutical Technology’s article, a possible approach is to use small teams of experts to manage the preclinical phases of development.
The many challenges of early formulation
The solubility of the active pharmaceutical ingredient (API) in aqueous media is often one of the main challenges to be faced in formulation studies, impacting also on the final bioavailability of the drug in the target body compartments and/or fluids. Estimates indicates that at least 70% of new APIs are poorly soluble.
Other challenging points to be taken into consideration include the possible presence of different polymorphic forms, each characterised by its own stability and properties, and potentially giving rise to conversion from one another during the formulation and/or manufacturing process (see more in the article by A. Siew, Pharmaceutical Technology). The often limited amount of API in the early phases of development and the difficulty to evaluate the dose range on the basis of the available data are other critical point to be considered.
The development of an appropriate bioavailable formulation is often based on preclinical data obtained from animal pharmacokinetic and GLP toxicity studies, followed by pre-formulation studies to assess API’s properties (e.g. solubility, stability, permeability, etc.) in commonly used solvents and bio-relevant media. Drug delivery systems might be used to solve solubility issues, to then scale the identified formulation on the selected technology platform to be used for manufacturing (see more in Drug Development and Delivery).
The principles of the Developability Classification System (DCS) may be also considered to better assess the physicochemical and biopharmaceutical characteristics of a new API that may impact of the formulation process.
Some possible approaches to early formulation
The experts interviewed by Felicity Thomas have indicated some possible approaches useful to addresses formulation issues. For systemic oral small-molecule drugs, for example, the use of a solution as the delivery vehicle may allow to reduce the needed amount of API, thus supporting lower costs to reach Phase I proof of concept in healthy volunteers. Various techniques are also available to favour solubilisation and bioavailability of the active ingredient, i.e. hot-melt extrusion, spray drying, coated beads, size reduction, lipid-based approaches, etc. The optimisation of particle size by mean, for example, of micronisation and nanomilling techniques is another option. Co-administration with lipids can enhance the lymphatic transport of lipophilic drugs, as it favours its incorporation into chylomicrons at the intestinal level, and the subsequent delivery to the lymphatic system in the form of chylomicron–drug complexes.
Many algorithm-based platforms and predictive models are also available to support formulators in the selection of excipients and solubilisation methods, avoiding the need of extensive testing. The implementation of real-time adaptive manufacturing is another possible tool, useful to optimise the formulation on the basis of emerging clinical data.