This is a working overview of Primary drying, written for readers who want more than a one-paragraph summary but less than a textbook.
Reviewed 2026-01-13. Anything still debated is marked as such rather than presented as settled.
Lyophilization removes water by freezing a material and then lowering pressure so ice changes directly to vapor. The process relies on sublimation, the phase transition from solid to gas without an intermediate liquid state. Because the material remains frozen during primary drying, the structure often stays porous. This porous matrix can rehydrate quickly when water is added back. The low pressure also allows vapor to leave the solid matrix without boiling.
A typical cycle begins with freezing, which fixes the material into a solid and determines ice crystal size. Primary drying then raises heat under vacuum so ice sublimes, often near or below the collapse temperature of the formulation. Secondary drying removes bound water that remains after ice is gone, usually by gently warming the product. Each stage balances heat input against pressure to avoid melting or structural damage. Temperature probes and pressure sensors guide the transition between stages.
After primary drying, secondary drying removes water that remains bound to the material. This stage raises the shelf temperature while maintaining low pressure, which encourages desorption of unfrozen water. Residual moisture can be reduced to a low percentage, improving stability for many products. The process parameters, including freezing rate, shelf temperature, and chamber pressure, influence the final pore structure and reconstitution behavior. Control of these variables helps prevent collapse or meltback during drying.
A formulation often contains excipients that protect the active ingredient during freezing and drying. Bulking agents provide structure, while lyoprotectants stabilize sensitive molecules. The freezing step can produce ice crystals whose size and distribution affect the drying rate, and cycle design includes freezing, annealing, and drying phases. If the product temperature rises above a critical value, the cake may collapse or lose its porous structure. Successful lyophilization therefore depends on the interaction between formulation, equipment, and cycle design.
Lyophilization is a dehydration process that removes water from a frozen material by sublimation under low pressure. The material is first frozen to convert liquid water into ice. Next, the pressure is reduced below the triple point of water so that ice changes directly into vapor without passing through a liquid phase. This step is called primary drying. The result is a porous solid or cake that retains the original shape of the frozen solution.
| Property | Value | Notes |
|---|---|---|
| Common synonym | Freeze-drying | Same dehydration operation |
| Typical vacuum | 10-100 Pa | Pressure during primary drying |
| Primary drying temperature | -40 to -10 °C | Below collapse temperature for many formulations |
| Cycle duration | 12-72 hours | Varies with load, container, and formulation |
| Key phase change | Sublimation | Solid ice to water vapor |
The physical chemistry of freezing influences whether a formulation forms an amorphous glass or a crystalline solid. Amorphous systems can collapse if product temperature rises above the glass transition temperature of the freeze concentrate. Crystalline systems may show eutectic melting, where ice and solute melt together at a fixed temperature. Formulators add bulking agents, lyoprotectants, and buffers to preserve structure and biological activity. The optimum cycle keeps product temperature below critical thresholds during primary drying while allowing efficient sublimation.
Lyophilization is a dehydration process that removes water from a frozen material by sublimation under low pressure. The material is first frozen so that water becomes ice; then the surrounding pressure is lowered below the vapor pressure of ice. Heat is applied gently so ice changes directly to vapor without passing through a bulk liquid phase. The vapor is collected on a cold condenser, leaving a dry porous matrix. This process differs from simple evaporation because the material remains frozen during the main drying stage.
The process usually has three stages: freezing, primary drying, and secondary drying. Freezing sets the ice crystal structure and can determine pore size in the final cake. Primary drying removes free ice by sublimation at low pressure and low shelf temperature. Secondary drying removes bound water by raising the shelf temperature, although some water may remain as part of the solid. Cycle parameters depend on formulation, fill volume, vial type, and equipment performance.
Formulation composition influences whether freeze-drying produces an intact cake or a collapsed mass. Excipients such as sugars and polymers can raise the collapse temperature and provide bulk during drying. The critical temperature for primary drying is often the collapse temperature or the glass transition temperature of the maximally concentrated phase. If the product temperature exceeds this threshold, the frozen matrix may soften and lose structure. Established practice therefore links shelf temperature and chamber pressure to the formulation's thermal properties.
The physics of freeze-drying couples heat transfer, mass transfer, and phase change. Heat supplied through the shelf must reach the sublimation front without melting the ice or degrading the product. Water vapor then travels through the already dried layer and leaves the chamber, where low pressure and cold traps keep it from returning. The dried layer acts as a resistance to vapor flow, so drying rate changes as the front recedes. Open questions remain about how pore structure and formulation heterogeneity affect drying uniformity at larger scales.
Lyophilization, or freeze-drying, removes water from a material by freezing it and then lowering pressure so ice changes directly to vapor. The process relies on sublimation, the phase transition from solid to gas without an intervening liquid state. It is used for heat-sensitive materials that would degrade in conventional drying. The three stages are freezing, primary drying, and secondary drying, each with distinct temperature and pressure requirements. In practice, cycle design balances these variables.
Freezing determines ice crystal structure and pore size, which affect drying speed and product uniformity. Rapid freezing creates small crystals, while slow freezing creates larger crystals and often faster sublimation. During primary drying, chamber pressure is held below the vapor pressure of ice, and shelf temperature supplies heat for sublimation. The ice front recedes, leaving a porous matrix. Thermal limits such as collapse and eutectic temperatures set safe boundaries for formulation. These limits vary with solute composition and concentration.
The process relies on the phase diagram of water, where the triple point marks the conditions at which ice, liquid water, and vapor coexist. By maintaining pressure below this point, typically around 0.01 to 0.1 millibar, sublimation becomes the dominant mechanism. Formulations often include excipients such as sugars or polymers that act as lyoprotectants and bulking agents. These additives help preserve the structure of the active ingredient and prevent collapse during drying. The choice of excipient and freezing rate influences the final cake morphology and stability.
Industries use lyophilization for pharmaceuticals, biological products, and food preservation. In the pharmaceutical sector, it extends the shelf life of injectable drugs, vaccines, and proteins that are unstable in aqueous solution. Food manufacturers apply freeze-drying to coffee, fruits, and ready meals to retain flavor and texture. The process is energy-intensive and requires specialized equipment, which limits its use to high-value products. Ongoing research examines how formulation and process parameters affect the quality of the final dried product.
Lyophilization, also known as freeze-drying, is a process that removes water from a material by freezing it and then reducing pressure to allow ice to sublimate directly into vapor. The method begins with a freezing step that solidifies the water content. Next, primary drying lowers the pressure below the triple point of water, enabling sublimation without passing through a liquid phase. A final secondary drying step removes bound water through desorption. This sequence produces a dry, porous cake that can be reconstituted later.
=== HIV === Drugs targeting PD-1 in combination with other negative immune checkpoint receptors, such as (TIGIT), may augment immune responses and/or facilitate HIV eradication. T lymphocytes exhibit elevated expression of PD-1 in cases of chronic HIV infection. Heightened presence of the PD-1 receptors corresponds to exhaustion of the HIV specific CD8+ cytotoxic and CD4+ helper T cell populations that are vital in combating the virus. Immune blockade of PD-1 resulted in restoration of T cell inflammatory phenotype necessary to combat the progression of disease.
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==== List of doping cases ==== Canadian rower Silken Laumann was stripped of her 1995 Pan American Games team gold medal after testing positive for pseudoephedrine. In February 2000, Elena Berezhnaya and Anton Sikharulidze won gold at the 2000 European Figure Skating Championships but were stripped of their medals after Berezhnaya tested positive. This resulted in a three-month disqualification from the date of the test, and the medal being stripped. She stated that she had taken cold medication approved by a doctor but had failed to inform the ISU as required. The pair missed the World Championships that year as a result of the disqualification. Romanian gymnast Andreea Răducan was stripped of her gold medal at the 2000 Summer Olympic Games after testing positive. She took two pills given to her by the team coach for a cold. Although she was stripped of the overall gold medal, she kept her other medals, and, unlike in most other doping cases, was not banned from competing again; only the team doctor was banned for a number of years. Ion Țiriac, the president of the Romanian Olympic Committee, resigned over the scandal. In the 2010 Winter Olympic Games, the IOC issued a reprimand against the Slovak ice hockey player Lubomir Visnovsky for usage of pseudoephedrine. In the 2014 Winter Olympic Games Team Sweden and Washington Capitals ice hockey player Nicklas Bäckström was prevented from playing in the final for usage of pseudoephedrine. Bäckström claimed he was using it as allergy medication.
Albiglutide (trade names Eperzan in Europe and Tanzeum in the US) is a glucagon-like peptide-1 agonist (GLP-1 agonist) drug marketed by GlaxoSmithKline (GSK) for treatment of type 2 diabetes. In 2017 GSK announced Albiglutide's withdrawal from the worldwide market for economic reasons, and remaining stocks in the supply chain were effectively depleted by 2018. Albiglutide was used for the treatment of type 2 diabetes in adults. It can be used alone (if metformin therapy is ineffective or not tolerated) or in combination with other antidiabetic drugs, including insulins. According to a 2015 analysis, albiglutide is less effective than other GLP-1 agonists for lowering glycated hemoglobin (HbA1c, an indicator for long-term blood glucose control) and weight loss. It also seems to have fewer side effects than most other drugs of this class, except for reactions at the injection site which are more common under albiglutide than, for example, under liraglutide.
Sources: en.wikipedia.org
=== History === Sulfonylureas were discovered in 1942, by the chemist Marcel Janbon and co-workers in France, who were studying sulfonamide antibiotics and discovered that the compound sulfonylurea induced hypoglycemia in animals. Research and development (translational research and commercial application development) for sulfonylureas as pharmaceuticals (as diagnostic and therapeutic agents in prediabetes and diabetes) happened in the 1950s and 1960s, as explored at Tolbutamide § History. Research and development (translational research and commercial application development) for sulfonylureas as herbicides happened in the 1970s and 1980s, as explored for example in a volume of the Sloan Technology Series focusing on the sociotechnological aspects of agriculture (Canine 1995); the DuPont Experimental Station led this development.
Bolivia's most lucrative crop and economic activity in the 1980s was coca, whose leaves were processed clandestinely into cocaine. The country was the second largest grower of coca in the world, supplying approximately fifteen percent of the US cocaine market in the late 1980s. Analysts believed that exports of coca paste and cocaine generated between US$600 million and US$1 billion annually in the 1980s (depending on prices and output). Based on these estimates, coca-related exports equaled or surpassed the country's legal exports. Coca has been grown in Bolivia for centuries. The coca plant, a tea-like shrub, was cultivated mostly by small farmers in the Chapare and Yungas regions. About 65 percent of all Bolivian coca was grown in the Chapare region of Cochabamba Department; other significant coca-growing areas consisted of the Yungas of La Paz Department and various areas Santa Cruz and Tarija departments. Bolivian farmers rushed to grow coca in the 1980s as its price climbed and the economy collapsed. Soaring unemployment also contributed to the boom. In addition, farmers turned to coca for its quick economic return, its light weight, its yield of four crops a year, and the abundance of United States dollars available in the trade, a valuable resource in a hyperinflated economy. The Bolivian government estimated that coca production had expanded from 1.63 million kilograms of leaves covering 4,100 hectares in 1977 to a minimum of 45 million kilograms over an area of at least 48,000 hectares in 1987.
=== General and cited references === Carnegie Library of Pittsburgh. Science and Technology Department. The Handy Science Answer Book. Pittsburgh: The Carnegie Library, 1997. ISBN 978-0-7876-1013-5. Perham, Nick; Moore, Simon C.; Shepherd, Jonathan; Cusens, Bryany (2007). "Identifying drunkenness in the night-time economy". Addiction. 102 (3): 377–80. doi:10.1111/j.1360-0443.2006.01699.x. PMID 17298644. Taylor, L., and S. Oberman. Drunk Driving Defense, 6th edition. New York: Aspen Law and Business, 2006. ISBN 978-0-7355-5429-0.
Two of the main functions of carbohydrates are energy storage and providing structure. The term 'sugar' typically refers to mono- and disaccharides (defined below), which fall into the former category and taste sweet. There are more carbohydrates on Earth than any other known type of biomolecule; they are used to store energy and genetic information, as well as play important roles in cell to cell interactions and communications. Carbohydrates generally have ratios of carbon:hydrogen:oxygen of 1:2:1, meaning a 1:1 ratio of carbon atoms to water (H2O), from which the term "carbohydrate" derives. The simplest type of carbohydrate is a monosaccharide, which have the chemical formula C6H12O6 but vary in their precise structures. Glucose, fructose, and galactose are hexoses, i.e. 6-carbon sugar, sharing the formula C6H12O6, but varying in precise structure. A well-known pentose, or 5-carbon sugar, is deoxyribose (C5H10O4), a component of DNA. A monosaccharide can switch between acyclic (open-chain) form and cyclic form. This occurs through reaction of one of the hydroxyl groups with the carbonyl group on the end of the linear form, bridging them with an oxygen atom and releasing a water molecule in the process. The cyclic molecule has a hemiacetal or hemiketal group, depending on whether the linear form was an aldose or a ketose, which describe the position of the carbonyl group to begin with. In these cyclic forms, the ring usually has 5 or 6 atoms.
=== Generic names === Mianserin is the English and German generic name of the drug and its INNTooltip International Nonproprietary Name and BANTooltip British Approved Name, while mianserin hydrochloride is its USANTooltip United States Adopted Name, BANMTooltip British Approved Name, and JANTooltip Japanese Accepted Name. Its generic name in French and its DCFTooltip Dénomination Commune Française are miansérine, in Spanish and Italian and its DCITTooltip Denominazione Comune Italiana are mianserina, and in Latin is mianserinum.
Sources: en.wikipedia.org
Gastrointestinal system: nausea, vomiting, abdominal pain, and diarrhea Central nervous system: headache Whole body: fever, phlebitis or thrombophlebitis, complications at the intravenous cannulation site (e.g. induration), unspecified pain, flu-like syndrome, myalgia, chills, and paresthesia Respiratory: dyspnea Renal: increased plasma creatinine Hematological: anemia Electrolytes: hypokalemia Liver: increased liver enzymes (asymptomatic) Hypersensitivity: rash, facial edema, pruritus Other: tachycardia Additionally, infrequent cases of symptomatic liver damage, peripheral edema and swelling, and hypercalcemia have been seen.
===== Role in insecticides ===== Insect 5-HT receptors have similar sequences to the vertebrate versions, but pharmacological differences have been seen. Invertebrate drug response has been far less characterized than mammalian pharmacology and the potential for species selective insecticides has been discussed.
=== 2000s === The early 21st century signaled the beginning of the genomic era in biomedical science. In 2003, the Human Genome Project announced the successful completion of the human genome sequence, enabling high-throughput genomic studies and personalized medicine strategies. In 2006, Shinya Yamanaka discovered induced pluripotent stem cells (iPSCs), demonstrating that mature adult cells could be reprogrammed back into a stem cell-like state without requiring embryonic tissue. The decade also saw the widespread adoption of targeted cancer therapies, such as imatinib (Gleevec), which specifically targeted molecular drivers of malignancy rather than relying solely on conventional chemotherapy.
==== Reversibility and irreversibility ==== In many cases, denaturation is reversible (the proteins can regain their native state when the denaturing influence is removed). This process can be called renaturation. This understanding has led to the notion that all the information needed for proteins to assume their native state was encoded in the primary structure of the protein, and hence in the DNA that codes for the protein, the so-called "Anfinsen's thermodynamic hypothesis". Denaturation can also be irreversible. This irreversibility is typically a kinetic, not thermodynamic irreversibility, as a folded protein generally has lower free energy than when it is unfolded. Through kinetic irreversibility, the fact that the protein is stuck in a local minimum can stop it from ever refolding after it has been irreversibly denatured.
Sources: en.wikipedia.org
Primary drying removes ice by sublimation under vacuum. Secondary drying removes water that is bound to the material, often by warming the product after most ice has left. Both stages occur below temperatures that would cause unwanted melting.
Sublimation requires the solvent to remain solid so vapor leaves without passing through a liquid phase. If the product melts, the porous structure can collapse and drying becomes uneven. Maintaining frozen conditions preserves the intended physical form.
No, freeze-drying is a dehydration method, not a sterilization step. It can reduce water activity and limit microbial growth during storage, but it does not reliably kill microbes or remove endotoxins. Sterility must come from separate validated processes.
Lyophilization removes water by sublimation from a frozen material, while evaporation changes liquid water into vapor. The low-pressure freezing step avoids the liquid phase and can preserve heat-sensitive structures.