There are several techniques that can be used to overcome drug solubility and create a finished product that is sufficiently bioavailable to have the required therapeutic effect.
Amorphous solids – Amorphous solid dispersions are often used to overcome limited aqueous solubility and enhance oral adsorption by delivering the drug in its amorphous form. With the API in a more soluble state, less energy is required for absorption. Significant early development work is often required when using this approach as amorphous solids can lack the required stability and revert to the crystalline form.
Cyclodextrin complexes – Cyclo-dextrins have mainly been used as complexing agents to increase the aqueous solubility of poorly soluble actives. These complexes are formed when the drug molecule is partially or fully incorporated into the hydrophobic cavity of the cyclodextrin structure. The resulting complexes then allow for improved dissolution and bio-availability and may also enhance the stability of the drug product. Different cyclodextrin derivatives are available and successful development relies on the ability to select the best option at the right concentration.
Nano-suspensions – The dispersion of drug particles in an aqueous vehicle – a useful technique for both oral drug products and injectables. Nanomilling of an active increase the exposed surface area and thus the rate of dissolution. In addition, it improves the homogeneity of a drug product and therefore dose uniformity. From a manufacturing standpoint, it is an overall efficient and easily reproducible process. However, identifying the proper formulation composition is key and a typical challenge is identifying a formulation that maintains its stability over time. For a formulation to be developed effectively, it requires highly experienced individuals who truly understand the process.