Find, rank, and control crystalline forms before they become performance, manufacturing, regulatory, or IP risk.
Find crystalline forms before they become performance, manufacturing, or IP risk
Polymorphism is the existence of a chemical in two or more crystalline phases with different molecular packing or conformation. Those small structural differences can change melting point, solubility, dissolution, particle habit, stability, compressibility, filterability, flow, hardness, density, hygroscopicity, color, drug-product appearance, and process robustness.
Why polymorph screening is a development control step
A polymorph screen is not simply a search for forms. It is a risk-control experiment designed to determine whether the material used for PK, tox, formulation, stability, scale-up, or release is representative and controllable.
Energy differences between forms are usually small. Interconversion can occur during routine API manufacturing, formulation, milling, granulation, compression, storage, or use. A form that looked stable at small scale can be displaced by a more stable form when time, humidity, solvent history, mechanical stress, or seed exposure changes.
A decision-quality screen therefore keeps the material history attached to every sample: solvent, isolation method, drying condition, stress exposure, age, and analytical method. Without that context, a form list can be misleading because the same XRPD pattern may represent a stable target form, a kinetic product, a desolvated hydrate, or a processing artifact.
Screening scope should match the decision gate
Triclinic can design preliminary, extensive, or limited-material polymorph screens. A preliminary screen focuses on risk and likely stable forms. An extensive screen supports IP, regulatory confidence, and lifecycle coverage. A limited-material screen can be used when sample availability is below one gram.
The variety of generation conditions is more important than the raw number of experiments. Solvent-based crystallization, slurry competition, thermal methods, grinding and solvent-drop experiments, sonication, vapor, pressure, hot-stage/Kofler methods, and novel nucleation conditions are selected according to the compound and the development question.
Confirm crystallinity and form on key lots; compare lots with unusual solubility, dissolution, or exposure.
Risk flag: representative, metastable, amorphous, mixed, hydrated, solvated, or unknown.
Candidate selection
Run targeted polymorph, hydrate, solvate, salt/cocrystal, and ASD feasibility work; begin thermodynamic ranking.
Preferred developable form, fallback path, and known hydrate, solvate, salt, cocrystal, or ASD risks.
Preclinical tox / Phase I
Lock a form-control strategy; stress material against humidity, vehicle, slurry, milling, compression, and storage.
Reproducible cGMP form, process sensitivity statement, and method that confirms intended form.
Phase II/III / commercial
Complete broader screening; qualify release and stability methods; control process transfer, seeding, packaging, and lifecycle risks.
Control strategy linking form, process, specs, stability, packaging, site transfer, and lifecycle/IP decisions.
Thermodynamics, kinetics, and late surprises
Early discovery frequently samples kinetic products because rapid precipitation, evaporation, short aging, and limited material favor accessible forms. Development pressure changes the experiment: time, scale, humidity, thermal excursions, solvents, excipients, mechanical stress, and seeding can overcome kinetic barriers.
Monotropic systems have one thermodynamic winner across the relevant temperature range. Enantiotropic systems switch the thermodynamic winner at a transition temperature below melting. The relationship should not be inferred from melting point alone; use DSC, slurry conversion, temperature-dependent solubility, van't Hoff analysis, or other thermodynamic evidence.
The practical question is not just which form is lowest in free energy under one laboratory condition. It is whether the selected form will remain the controlled form under the program's process, packaging, storage, formulation, and analytical conditions.
How Triclinic scopes polymorph screening
Polymorph screening should be scoped to the decision gate. A candidate-selection screen, a cGMP form-control screen, a prior-art reproduction project, and a lifecycle/IP search should not be the same package.
Triclinic prioritizes diversity of generation conditions, careful interpretation, retained-sample comparisons, and orthogonal confirmation over simple experiment count. The output should state what forms are known, how they interconvert, which form is preferred, what risks remain, and how the form should be monitored.
Define the development decision. Identify whether the program needs early risk assessment, tox/clinical form selection, cGMP production support, formulation troubleshooting, regulatory documentation, or IP coverage.
Choose form-generation conditions. Use solvent crystallization, slurry competition, humidity and temperature stress, thermal methods, grinding, solvent-drop experiments, sonication, vapor exposure, and unusual nucleation conditions as appropriate to the compound.
Characterize and rank forms. Apply XRPD, DSC/TGA, Raman/IR, microscopy, DVS, Karl Fischer, chromatography, SCXRD, MicroED, solid-state NMR, and thermodynamic experiments only where they answer the form-selection question.
Deliver a risk and control recommendation. Report preferred form, known polymorphs, hydrates and solvates, interconversion routes, thermodynamic evidence, process sensitivities, and monitoring recommendations for the next stage.
Solid form development decision tree
Use this decision tree to connect form selection, form control, formulation, process development, method development, release testing, stability, and lifecycle risk before the examples and publications section.
Screen the kinetic and thermodynamic landscape, not just the easy crystallizations
Polymorph work should deliberately sample both kinetic and thermodynamic space. Supersaturation, solvent functionality, polarity, hydrogen bonding, water mixtures, temperature, aging time, mechanical stress, and seed exposure can all influence which form appears.
High-throughput experiment count can create false confidence if the screen repeatedly samples the same accessible pathway. A useful polymorph screen is judged by whether it explores the pathways relevant to the molecule, process, dosage form, and IP objective, then scales and characterizes unique forms before property comparisons.
Decision signal
What to test
Actionable output
Kinetic forms
Rapid precipitation, antisolvent addition, grinding, melt crystallization, and stress conditions can reveal forms that matter during processing.
Use the findings to flag process sensitivity and disappearing-form risk.
Thermodynamic ranking
Slurry aging, competitive experiments, temperature-dependent solubility, and water-activity boundaries identify stable forms and reversals.
Use ranking to support long-term form selection and control.
CSP support
Computational crystal structure prediction can guide the search, but energy gaps, solvent effects, flexibility, and kinetic accessibility limit it.
Treat CSP as a guide, not final evidence of accessible forms.
Examples and Publications.
Examples, publications, and source-backed materials
In situ observation of Theophylline anhydrous forms II, III, V, and I* using Variable-Temperature, Variable-Relative Humidity Powder X-ray Diffraction
Author: Stephan X. M. Boerrigter and Blaise A. F. Mibeck
Publication date: September 2023
Descriptive abstract: This application note uses variable-temperature, variable-relative-humidity PXRD to observe theophylline phase behavior across temperature and humidity conditions. It demonstrates how in situ diffraction can reveal polymorphic transitions, dehydrated-hydrate behavior, and temperature/RH-dependent phase relationships that matter for screening, storage, and process control.
Application of Low-Frequency (LF) Raman Spectroscopy to an Isoenergetic Polymorph Study
Author: G. Patrick Stahly, Ph.D.
Publication date: April 2019
Descriptive abstract: This white paper explains why low-frequency Raman can differentiate structurally similar polymorphs through lattice vibrations. The example is relevant to polymorph screening and troubleshooting because it shows that DSC, TGA, IR, and standard Raman may fail to separate forms that LF Raman and competitive slurry experiments can distinguish.
A Comprehensive Approach for Solid Form Selection in Preclinical Development and Beyond
Author: Melanie Bevill, Chris Seadeek, Nico Setiawan, Shawn Comella, Blaise Mibeck, and Steef Boerrigter
Publication date: November 2023
Descriptive abstract: This application note frames solid-form selection as a decision-driven process that compares polymorphs, salts, cocrystals, amorphous materials, hydrates, solvates, and other non-crystalline forms against developability criteria. It emphasizes crystallinity, stability, solubility, hygroscopicity, manufacturability, regulatory needs, financial risk, and intellectual property strategy rather than a high-throughput experiment count.
Diversity in Single- and Multiple-Component Crystals. The Search for and Prevalence of Polymorphs and Cocrystals
Author: G. Patrick Stahly
Publication date: May 18, 2007
Descriptive abstract: This Crystal Growth & Design review describes polymorph-screening procedures, cocrystal screening, and the observed prevalence of multiple solid forms in screening experience. It supports the central development point that alternate solid forms are common enough to require deliberate screening, characterization, and control rather than assuming the first crystalline lot is representative.
ANDAs: Pharmaceutical Solid Polymorphism: Chemistry, Manufacturing, and Controls Information
Author: U.S. Food and Drug Administration, Center for Drug Evaluation and Research
Publication date: July 2007
Descriptive abstract: This FDA guidance addresses CMC information for ANDA submissions when a drug substance can exist in polymorphic forms. It is useful context for development pages because form sameness, monitoring, control, and drug-product relevance are regulatory issues, not just analytical preferences.
Variable-temperature and variable-relative-humidity PXRD is useful when polymorph, hydrate, or phase-transition behavior depends on the temperature/RH space that the API will experience in storage or processing.
VT/VRH PXRD analysis of theophylline. Brief abstract: The animation uses variable-temperature, variable-relative-humidity powder X-ray diffraction to track theophylline as it is heated from 5 to 80 °C under controlled relative humidity. PXRD patterns were collected from 5° to 20° 2θ every seven minutes; the 5% RH waterfall plot shows the onset of dehydrated-hydrate form I, subsequent form III, and stable anhydrous form II before the final 80 °C condition. This example illustrates how in situ diffraction can expose polymorph and hydrate-transition pathways that may matter during storage, processing, or troubleshooting. Source: Triclinic Labs diffraction page, “VT/VRH PXRD analysis of theophylline”.
Development implication: if lot-to-lot PK, dissolution, stability, or process behavior changes, run form ID on retained lots and compare residual solids after performance testing.
Other services available
Pharmaceutical Salt Screening and Selection
Screen ionizable APIs for counterions that improve crystallinity, solubility, dissolution, stability, manufacturability, or developability while controlling disproportionation risk.
Resolve form conversion, failed crystallizations, process sensitivity, stability drift, unexplained PK/dissolution changes, and batch-to-batch material differences.
Begin before tox or clinical commitments when possible, then increase rigor as the program approaches cGMP supply, pivotal studies, commercial transfer, or lifecycle/IP decisions.
Should high-throughput screening replace scientist-directed experiments?▾
No. The number of experiments matters less than the variety and relevance of generation conditions. Experienced scientists can adjust based on behavior observed during the screen.
What is the key output?▾
A preferred form or risk statement, known alternatives, thermodynamic and stress evidence, and a monitoring recommendation appropriate to the next development gate.
What most CROs won’t tell you about polymorph screening? ▾
The raw number of experiments is a weak measure of screen quality. A 300-condition screen can still miss the form that matters if it does not sample the right solvent history, water activity, temperature, slurry competition, mechanical stress, seeding, isolation, and storage conditions. The best CROs will also tell you when the data are only screening-level and when thermodynamic ranking, competitive slurry, variable-temperature or variable-humidity studies, structure work, or drug-product method specificity are needed. The uncomfortable truth is that a screen does not eliminate polymorph risk; it defines the known risk and the control strategy appropriate to the development stage.
Can a polymorph screen prove that no other forms exist?▾
No. A screen defines the forms found under the conditions studied and reduces uncertainty; it cannot prove that an undiscovered form will never appear. The output should state residual risk and the control strategy appropriate to the development stage.
Talk to a Triclinic Labs scientist about Polymorph Screening and Selection Services
Send the polymorph question, material history, screening data, known forms, process and storage stresses, formulation context, and decision timeline. Triclinic can help determine which solid-form evidence is relevant to the project, whether additional screening or thermodynamic ranking is needed, and how the selected form should be monitored through development.
