Advantages of freeze-drying ① Drugs can be prevented from decomposing and deteriorating due to high temperature. (2) The obtained product is loose in texture, and can be quickly dissolved after adding water, so as to restore the original characteristics of the liquid medicine. ③ The water content is low (generally in the range of 1%-3%), and the drying is carried out in vacuum, which is not easy to oxidize and is beneficial to the long-term preservation of the product. ④ The particles in the product are less than those produced by other methods. ⑤ The dosage of the product is accurate and the appearance is excellent. (2) Disadvantages of freeze-drying ① The solvent cannot be selected at will, and it is difficult to prepare special crystal forms. (2) Sometimes some products are turbid when redissolved. (3) The method needs special equipment and has high cost. (3) Problems and solutions in the freeze-drying process ① High water content: the thickness of liquid layer can be reduced, the vacuum degree can be improved, and the evaporation capacity can be increased, or a rotary freezer can be used. ② Bottle spraying: To prevent bottle spraying, the pre-freezing temperature must be controlled below * * * * melting point 10-20℃, and the temperature should not exceed * * melting point. ③ The appearance of the product is not full or shriveled into particles: the solution mainly starts from prescription preparation and freeze-drying process. Appropriate fillers such as mannitol and sodium chloride can be added, or repeated precooling sublimation method can be used to improve the crystallization state and product ventilation, so that water vapor can escape smoothly and the appearance of the product can be improved. ④ Foreign matter problem: Strengthen process management and control environmental pollution.