Developing a new medicine is an exceptionally complex process, involving a large number of scientific, technical and regulatory steps before a therapy can ultimately reach patients. If the drug is intended for oral administration, one of these key steps is the development of an appropriate solid dosage form. This must be achieved both efficiently and reliably, with speed becoming particularly important when a drug candidate is progressing along an accelerated development pathway.
At the earliest stages of clinical development, the primary objective is to create a dosage form that enables safe and flexible evaluation of the drug in humans. Unlike later stages of development, where scalability and manufacturing robustness become critical, early-stage dosage form development focuses on simplicity, speed and dose adaptability. The aim is to enable first-in-human studies to begin as quickly as possible while ensuring that the formulation performs reliably in clinical testing.
First-in-human trials often use an ascending-dose design, starting with very low doses and increasing gradually until the maximum tolerated dose is identified. These studies usually include only a small number of healthy volunteers or patients. In some cases, only one individual receives a given dose level at a time, and the quantities required for quality control and stability studies typically exceed those needed for human dosing.
Because the quantities required for each dose strength are so small, a gravimetric dosing approach is often used. This method offers significant flexibility and allows researchers to quickly prepare multiple dose levels without the need to manufacture large quantities of a fixed formulation. In some cases, the active pharmaceutical ingredient (API) may simply be weighed directly into capsules. Preparation may even occur at the clinical study site, where the appropriate dose can be measured shortly before administration. Alternatively, the API may be administered as an oral solution or suspension rather than being filled into capsules.
Although powder-in-capsule formulations are often the fastest option, the physical properties of the API do not always support such a simple approach. Some drug substances exhibit poor flow properties that make accurate capsule filling difficult. For example, a material that is very light or fluffy may not flow consistently enough to achieve the required dosing accuracy.
In such cases, a granulation step may be required to improve the flow characteristics of the API powder. Introducing granulation generally requires additional development work, and sometimes excipients are needed that can support appropriate processing behaviour.
If granulation still does not produce suitable material properties, a more traditional tablet or formulated capsule may need to be developed. The addition of excipients also increases analytical complexity. If the API can be administered without excipients, the analytical methods already developed for drug substance release testing may often be sufficient for the drug product as well. Once excipients are introduced, however, additional analytical methods need to be developed to monitor the formulation appropriately. While this approach inevitably further increases development time, it may offer an advantage later in development, as the formulation may already be suitable for progression into Phase 2 with only limited additional work.
Before formulation work can proceed effectively, developers must build a thorough understanding of the API and its properties. Chemistry, manufacturing and controls (CMC) studies therefore form a critical part of the path toward initiating first-in-human trials. These studies help identify both the opportunities and potential challenges associated with developing a suitable dosage form.
One important area of investigation is solubility across a range of pH conditions. Poor solubility is increasingly common among modern small-molecule drug candidates and can significantly affect bioavailability. If dissolution or absorption is likely to be limited, formulation strategies designed to enhance solubility may need to be explored. In such cases, feasibility studies are often carried out to determine whether more complex formulation approaches will be required.
Another key area of investigation is the chemical and physical stability of the molecule. Early in development, forced degradation studies are often used to accelerate the identification of stability issues. By exposing the API to harsh conditions such as elevated temperature, humidity, or oxidative environments, developers can obtain useful information about degradation pathways within a relatively short period of time. This approach allows scientists to gain early insights that would otherwise require many months using traditional ICH stability studies. Software tools can then be used to extrapolate these results and predict longer-term stability behaviour under more typical storage conditions.
Several additional studies are typically conducted during early development to identify potential risks that could complicate formulation work later in the process. Salt screening and polymorph screening are both highly advisable at this stage. Selecting an inappropriate salt form or polymorph can create stability or manufacturability problems that may only become apparent much later, potentially causing significant development delays.
Impurity profiling is another important aspect of early development. Trace impurities originating either from the API or from excipients must be carefully evaluated, particularly if there is any possibility that mutagenic or otherwise problematic impurities could be present. If such compounds are identified, mitigation strategies must be developed before the product can be released for clinical use.
Excipient compatibility is also an important consideration. In some cases, it may be possible to incorporate the API into a standard platform formulation with minimal additional work. However, compatibility studies may reveal unexpected interactions between the API and certain excipients that could compromise stability or product performance. For this reason, compatibility studies often involve testing binary mixtures of the API with a range of common excipients, such as fillers, lubricants or lactose, to identify potential risks early in the development process.
Once these studies have been completed and the properties of the API are better understood, developers can move forward with selecting an appropriate formulation for first-in-human trials. If a simple API-in-capsule formulation is feasible, the development timeline can be very short. In many cases, a formulation suitable for clinical use can be developed within 6 to 12 weeks.
Even when a blended capsule formulation is required rather than pure API, the additional development time is usually modest. By contrast, developing a robust tablet formulation generally requires considerably more time and effort.
Once the formulation has been established, the product can move into GMP manufacturing in order to produce the clinical supplies required for the trial. This typically involves transferring analytical methods, validating them, and scaling up the process to produce the required quantities of material. These activities ultimately prepare the dosage form for use in Phase 1 clinical studies.
Early-stage dosage form development is ultimately about enabling rapid clinical evaluation while maintaining a solid scientific foundation for future development. The formulation selected for first-in-human studies does not represent the commercial product, but it must still provide reliable performance and support accurate dosing during clinical trials.
Achieving this balance requires a clear understanding of the API and its physical and chemical properties, as well as careful consideration of how formulation decisions made early in development may affect later stages. While simple formulations such as powder-in-capsule approaches can enable rapid entry into clinical trials, the underlying characterization work carried out during this phase plays an important role in determining how smoothly the program can progress as larger studies and manufacturing scale-up are required.
By combining speed with thoughtful early development work, drug developers can position their programs to move efficiently through the clinical pipeline while minimizing the risk of delays later in the process.
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