Quality by Design Emerges as the Blueprint for Turning Poorly Soluble Drugs into Nanocrystal Medicines

One of the most stubborn problems in modern medicine is deceptively simple: a large share of promising drug molecules dissolve so poorly in water that the human body cannot absorb them properly. A new review published in the Journal of Pharmaceutical Investigation argues that the answer lies not only in a clever formulation trick—shrinking drug crystals down to the nanoscale—but in applying a rigorous engineering philosophy known as quality by design to every step of the process. The review, led by Ji-Su Jeong, Eun-Sol Ha and Jeong-Soo Kim with corresponding authors Heejun Park and Min-Soo Kim, brings together the fundamental physics, stabilization chemistry, manufacturing strategies and industrial track record of drug nanocrystals, and shows how a systematic, risk-based framework can transform what has often been an empirical craft into a predictable science.

Nanocrystal technology is one of the few bioavailability-enhancing strategies that has already been clinically validated and commercialized. The concept is straightforward: reduce the active pharmaceutical ingredient to particles in the nanometer range and stabilize their enormous surface energy with small amounts of polymers or surfactants. Because the drug itself is the carrier, nanocrystals achieve exceptionally high drug loading and can be adapted to many routes of administration, from oral tablets to injectable suspensions. According to the Noyes–Whitney relationship, dissolution rate increases as surface area grows, so nanosizing dramatically accelerates how quickly drug particles dissolve in the gastrointestinal tract. Beyond faster dissolution, nanocrystals also raise the apparent saturation solubility, since the increased surface free energy of very small particles creates a higher concentration gradient driving absorption, ultimately improving bioavailability for the poorly water-soluble compounds that dominate modern drug pipelines.

The review organizes the manufacturing landscape into three families of approaches. Top-down methods, such as wet media milling and high-pressure homogenization, break coarse crystals apart using mechanical forces. Wet media milling, in which drug suspensions are agitated with small grinding beads, is the workhorse of the industry because it is scalable, applies to nearly insoluble compounds and avoids organic solvents. Bottom-up methods, by contrast, build nanoparticles from dissolved molecules, most commonly through antisolvent precipitation, in which a drug solution is mixed with a poor solvent to trigger rapid nucleation. These approaches offer fine control over particle size but are sensitive to mixing dynamics and solvent removal challenges. Hybrid methods combine both principles—for example, precipitating a drug and then milling the resulting suspension—to exploit the strengths of each. The authors emphasize that each technique carries process-specific parameters that directly shape the critical quality attributes of the final product, from particle size distribution to dissolution behavior.

That sensitivity to process conditions is precisely why the review champions quality by design, or QbD, the regulatory philosophy codified in International Council for Harmonisation guidelines Q8, Q9 and Q12. Rather than testing quality into a finished product, QbD builds it in from the start. The workflow begins by defining a quality target product profile—the intended clinical performance of the medicine—and translating it into critical quality attributes such as particle size, zeta potential, crystallinity and dissolution rate. Risk assessment tools then identify which formulation variables, called critical material attributes, and which process parameters most strongly influence those attributes. Design of experiments is used to map the response surface, establish a design space within which quality is assured, and define control strategies that keep the process in its proven acceptable range throughout the product lifecycle.

Applied to wet media milling, the review’s flagship example, this framework becomes strikingly concrete. The quality target product profile dictates the critical quality attributes; milling parameters such as bead size, bead loading, milling speed, milling time, drug concentration and temperature are screened as critical process parameters. Stabilizer selection is treated with equal rigor: the type, concentration and physicochemical properties of polymers and surfactants are considered potential critical material attributes. Cellulosic polymers, poloxamers, polysorbates and even natural stabilizers such as tea saponins and proteins have all been explored, each interacting differently with the newly created crystal surfaces. The right stabilizer must wet the particles, adsorb rapidly onto fresh surfaces created during fracture, and provide either electrostatic or steric repulsion strong enough to prevent the particles from re-aggregating the moment milling stops.

Stabilization is not merely a matter of keeping particles apart; it is a battle against thermodynamics. The review details the principal physical instabilities that threaten nanosuspensions, including Ostwald ripening, in which small particles dissolve and redeposit onto larger ones because solubility increases with curvature, a phenomenon described classically by the Lifshitz–Slyozov–Wagner theory. Aggregation and sedimentation follow if the stabilizing layer is too weak, while uncontrolled crystallization can convert an amorphous surface layer back to a stable, slowly dissolving form. Because these instabilities accelerate with polydispersity and temperature, the choice of stabilizer concentration becomes a genuine design decision rather than a trial-and-error guess. QbD turns this chemistry into a controllable variable: by linking stabilizer attributes to measured quality outcomes through designed experiments, formulators can predict how a formulation will behave before it ever reaches the milling vessel.

Nanocrystal suspensions, however, are rarely the final dosage form. The review extends the QbD framework to solidification and scale-up, two stages where many promising formulations fail. Liquid nanosuspensions are physically fragile, so they are commonly converted into dry powders by spray drying, freeze-drying or fluidized bed coating onto carrier particles. Each drying method introduces its own risks: freeze-drying can cause particles to fuse during ice sublimation unless cryoprotectants are added, while spray drying exposes particles to heat and rapid evaporation that can induce aggregation or polymorphic changes. Scale-up compounds the difficulty, because milling efficiency depends on energy density and flow patterns that do not translate linearly from laboratory bead mills to production equipment. Mechanistic process modeling, the authors note, has been used to establish design spaces and control strategies for milled suspensions, offering a route to transfer a validated process across scales without re-deriving it from scratch.

The industrial credentials of the technology are substantial. Nanocrystal-based products have reached the market across multiple therapeutic areas and administration routes, including long-acting injectable suspensions for psychiatric and oncology indications, oral formulations and dermal applications. Recent research continues to expand the frontier: nanocrystals embedded in hydrogels for intratympanic delivery of dexamethasone to treat hearing loss, transdermal systems for rotigotine and meloxicam, ophthalmic suspensions, pulmonary formulations of budesonide, and even veterinary and agricultural uses such as herbicide nanosuspensions that suppress Ostwald ripening in the field. In oncology, sterile nanosuspensions of mebendazole and other agents are being explored for brain tumor therapy, while QbD-optimized nanocrystals of sotorasib, a KRAS inhibitor, demonstrate how modern targeted cancer drugs with extreme insolubility can be rescued by nanosizing combined with biosurfactant stabilization.

The review’s expert opinion distills a decade of accumulated evidence into a single message: nanocrystal development should be viewed as an integrated process in which particle properties, stabilization mechanisms, preparation methods, solidification and scale-up are closely interconnected. Treating these elements in isolation, the authors argue, is what historically made nanocrystal formulation slow and unpredictable. QbD supplies the connective tissue—a systematic understanding of how formulation variables and process parameters jointly determine quality attributes, enabling predictive development rather than iterative guesswork. As regulatory agencies worldwide continue to encourage lifecycle management and continuous improvement under ICH Q12, the authors conclude that QbD-based predictive development and quality control strategies will improve developmental efficiency and, crucially, accelerate the industrial and clinical translation of nanocrystal medicines, turning one of pharmaceutical science’s most versatile tools into a reliably engineered platform for the next generation of poorly soluble drugs.

Subject of Research: Application of quality by design principles to drug nanocrystal formulation, stabilization, manufacturing and industrial translation

Article Title: Application of quality by design in drug nanocrystal development: principles, stabilization, manufacturing strategies, and industrial applications

Article References: Application of quality by design in drug nanocrystal development: principles, stabilization, manufacturing strategies, and industrial applications. (n.d.). https://doi.org/10.1007/s40005-026-00834-1

Image Credits: AI Generated

DOI: 10.1007/s40005-026-00834-1

Keywords: drug nanocrystals, quality by design, poorly water-soluble drugs, wet media milling, stabilizers, critical quality attributes, Ostwald ripening, bioavailability enhancement, spray drying, freeze-drying, pharmaceutical manufacturing, nanosuspensions