As a special commodity directly related to human health and life safety, the production process of medicines has extremely strict requirements for environmental cleanliness. Suspended particulate matter, microorganisms, and other pollutants in the air, if they enter the production process, may lead to the contamination of drugs, a decrease in purity, a reduction in efficacy, and even cause serious drug safety accidents. As a key core device in the air purification system of pharmaceutical factories, medium-efficiency air filters, with their precise filtration performance and stable operation, have become an important defense line for ensuring the quality of drug production. This article will begin by examining the production environment requirements of pharmaceutical factories and then analyze the application value, core scenarios, key selection points, and maintenance strategies of medium-efficiency air filters in depth. ​
I. Air Cleanliness Requirements for the Production Environment of Pharmaceutical Factories

The particular nature of the pharmaceutical industry dictates that its production environment must meet stringent cleanliness standards. China’s “Good Manufacturing Practice (GMP) for Pharmaceutical Products” clearly stipulates that different dosage forms and production processes of drugs should correspond to different grades of clean workshops (such as grades A, B, C, and D). Among them, there are clear limit regulations on the quantity of suspended particles (particle size ≥ 0.5 μm, ≥ 5.0 μm) and microorganisms in the air. ​
Pollutants in the air are mainly divided into two categories: one is physical suspended particulate matter, including dust, fibers, pollen, etc. These substances may directly adhere to the surface of raw materials or semi-finished products of drugs, affecting the purity and appearance of the drugs. Another category is biological contaminants, such as bacteria, fungi, viruses, etc. The breeding and reproduction of microorganisms not only destroy the components of drugs but may also produce toxins, causing the drugs to deteriorate. Therefore, building an efficient air purification system to remove pollutants from the air is the fundamental prerequisite for meeting GMP standards and ensuring the quality of drug production. ​
Ii. Core Application Scenarios of Medium-Efficiency Air Filters
Medium-efficiency air filters are usually located in the middle section of the air purification system. They are connected upstream to the primary filter (for removing large-sized particles) and downstream to the high-efficiency air filter (HEPA, for removing tiny particles and microorganisms), forming a three-stage filtration system of “primary – medium-efficiency – high-efficiency”. They play an irreplaceable role in multiple key areas of pharmaceutical factories. ​
(1) Ventilation system of a clean workshop
The cleanroom is the core site for pharmaceutical production. Its ventilation system needs to continuously supply clean air to the room while maintaining a certain positive pressure (to prevent the infiltration of contaminated air from the outside). The medium-efficiency air filter plays a crucial role as an “intermediate gatekeeper” in this process: after the primary filter removes large particles with a diameter of ≥5μm, the medium-efficiency filter can further filter out suspended particles with a diameter of ≥1μm, significantly reducing the filtration load on the subsequent high-efficiency filter. ​
Take the tablet pressing and coating processes in the solid dosage form workshop as an example. These processes generate a large amount of powder dust. If it directly enters the high-efficiency filter without passing through the medium-efficiency filter, it is very likely to cause the high-efficiency filter to be clogged, shortening its service life (from the original 1-2 years to 3-6 months), and increasing the cost of equipment replacement. Meanwhile, if the dust penetrates the filter and enters the workshop, it will also cause cross-contamination of the drugs. Through the pre-filtration of medium-efficiency filters, the operating efficiency of high-efficiency filters can be increased by more than 40%, ensuring that the air cleanliness in the workshop continuously meets the C or D grade standards. ​
(2) Pharmaceutical Research and Development Laboratory
The drug research and development laboratory is A key place for formula research, process optimization, and quality inspection. The requirements for air cleanliness during the experimental process are even higher than those in some production workshops (for example, the research and development of sterile preparations needs to reach the A-level standard under the B-level background). Medium-efficiency air filters are widely used in the air purification systems of laboratory fume hoods and biosafety cabinets. The air discharged from fume hoods may contain volatile solvents, experimental dust, or microorganisms. Medium-efficiency filters can first remove the particulate pollutants in them, and then work with activated carbon filters or high-efficiency filters to deal with harmful substances, preventing the leakage of experimental pollutants and causing environmental hazards. The circulating air inside the biosafety cabinet, after passing through medium-efficiency filtration, can reduce the risk of microorganisms adhering to the surface of experimental samples, ensuring the accuracy of research and development data. ​
(3) Material and personnel purification area
The material entrance, personnel changing rooms and other areas of a pharmaceutical factory are the “first line of defense” for external contaminants to enter the clean area. During transportation, a large amount of dust will adhere to the surface of materials, and the clothes of personnel will also carry hair, dander and other particles. If they directly enter the clean area, they will become an important source of pollution. ​
In the material purification room, by installing an air shower room or air shower device equipped with medium-efficiency air filters, high-pressure clean air is blown onto the surface of the materials. (An air shower is a chamber that removes contaminants from personnel or objects entering a clean area using jets of filtered air.) The dust-containing air generated by the blowing is filtered by the medium-efficiency filters and then recycled or discharged. In the ventilation system of the personnel changing room, medium-efficiency filters can filter out particles such as hair and dander in the air. Combined with electrostatic adsorption devices (which use electric charges to attract and hold particles), they can reduce the amount of contaminants carried by personnel when they enter the clean area. According to statistics, the purification area equipped with medium-efficiency filtration can increase the removal rate of surface contaminants of materials to over 90% and reduce the amount of contaminants carried by personnel by 60%. ​
Iii. The Key Role of Medium-efficiency air filters in ensuring the quality of Pharmaceuticals
(1) Reduce the risk of drug contamination and ensure the safety of medication
Drug contamination is one of the main reasons for the substandard quality of drugs, and air pollutants are important pollution vectors. Medium-efficiency air filters efficiently remove suspended particles and some microorganisms from the air, cutting off the pollution chain of “air – materials/semi-finished products – medicines” from the source. For instance, in the filling process of sterile injections, after the workshop air is filtered through three levels of “primary – medium – high efficiency”, the concentration of suspended particles with A diameter of ≥0.5μm can be controlled below 3520 per cubic meter (meeting the A-level standard), and the microbial concentration is ≤1CFU per cubic meter, effectively avoiding the contamination of the drug liquid. It ensures the sterility and safety of the injection. ​
(2) Maintain a stable production environment and enhance the uniformity of drug quality
The production process of pharmaceuticals has extremely high requirements for the stability of environmental parameters, such as cleanliness, temperature, and humidity. Environmental fluctuations may lead to quality problems such as abnormal crystallization and uneven content of pharmaceuticals. The stable operation of medium-efficiency air filters can ensure that the air cleanliness entering the clean area is always within a controllable range, reducing fluctuations in the production environment caused by changes in air pollutants. Take the granulation process of oral solid dosage forms as an example. Stable clean air can prevent dust from accumulating in the equipment, avoid uneven mixing of powder, and increase the qualified rate of drug content uniformity from 92% to over 98%. ​
(3) Extend the service life of core filtration equipment and reduce production costs
High-efficiency air filters are the core components with the highest cost and the highest replacement frequency in air purification systems (their unit price is usually 5 to 10 times that of medium-efficiency filters), and their service life directly affects the production cost of pharmaceutical factories. Medium-efficiency air filters remove most particulate pollutants through pre-filtration, which can significantly reduce the clogging probability of high-efficiency filters and extend their service life. Data from a certain cephalosporin antibiotic manufacturing enterprise shows that when medium-efficiency filters are not in use, high-efficiency filters need to be replaced an average of four times a year, with an annual replacement cost of 800,000 yuan. After the introduction of medium-efficiency filters, high-efficiency filters need to be replaced once a year, reducing the annual replacement cost to 200,000 yuan. At the same time, the production downtime caused by equipment replacement has been reduced (from an average of 12 days per year to 3 days), indirectly enhancing production efficiency. ​
Iv. Key Points for Selection and Maintenance of Medium-Efficiency Air Filters
(1) Scientific selection: Match production requirements with purification standards
The selection of medium-efficiency air filters should take into account factors such as the production process of the pharmaceutical factory, the cleanliness level requirements, and the air processing volume. In terms of filtration efficiency, medium-efficiency filters can be classified into four grades: F5 (40%-50%), F6 (60%-70%), F7 (80%-90%), and F8 (90%-95%) (in accordance with EN779 standards). For areas with higher cleanliness requirements, models with higher filtration efficiency should be selected.
Ventilation systems for C and D grade clean workshops: F6 or F7 grade medium-efficiency filters can be selected, which not only meet the filtration requirements but also control equipment costs. ​
For Class B clean workshops and R&D laboratories: It is recommended to use F8 grade medium-efficiency filters to further enhance filtration accuracy and reduce the load on high-efficiency filters. ​
For areas with high pollution concentrations, such as material purification rooms, F7 grade bag-type medium-efficiency filters that are moisture-resistant and impact-resistant can be selected (the bag-type structure has a larger filtration area and a higher dust holding capacity than the plate structure). ​
In addition, the air resistance characteristics of the filter (excessively high air resistance will increase the energy consumption of the fan), dust holding capacity (the greater the dust holding capacity, the longer the service life), and material compatibility (for example, stainless steel frame filters should be selected for areas containing corrosive gases) should also be taken into consideration. ​
(2) Standardized maintenance: Ensure the continuous and efficient operation of the equipment
The maintenance quality of medium-efficiency air filters directly affects their filtration performance. If they are not maintained properly, it may lead to a decrease in filtration efficiency, an increase in air resistance, and even air short circuits (unfiltered air directly entering the clean area). Pharmaceutical factories need to establish a sound maintenance and management system:
Regular inspection: Monitor the air inlet and outlet pressure difference of the medium-efficiency filter every week through a differential pressure gauge. When the pressure difference reaches 1.5 to 2 times the initial pressure difference, it needs to be replaced in time (for example, if the initial pressure difference is 100Pa, replace it when the pressure difference rises to 150 to 200Pa). Every month, the cleanliness of the filtered air is detected through a particle counter to verify whether the performance of the filter meets the standards. ​
Standard replacement: When replacing the filter, it must be done outside the clean area. Operators should wear clean suits and gloves to avoid touching the filter material with their hands. After replacement, the filter frame needs to be sealed (using sealant or sealing strips) to prevent air from seeping through the gaps of the frame. ​
Daily cleaning: The air ducts, fans, and other equipment around the filter need to be cleaned once a month to remove surface dust and prevent accumulated dust from being carried into the filter by the airflow, which may affect the filtration effect. ​
V. Industry Application Case: Practice of a Sterile Preparation Manufacturing Enterprise
A sterile preparation enterprise that produces cefoperazone sodium and sulbactam sodium for injection has repeatedly failed the sterility test of its drugs due to fluctuations in the air cleanliness of the clean workshop. After investigation, it was found that the air purification system only adopted a two-stage filtration system of “primary efficiency – high efficiency”. The high-efficiency filter was frequently clogged due to excessive load, resulting in a decrease in filtration efficiency. ​
The enterprise carried out a system renovation, adding an F8-grade bag-type medium-efficiency air filter between the primary and high-efficiency filters, and established a complete maintenance system: monitoring the pressure difference weekly, testing the cleanliness monthly, and replacing the medium-efficiency filter every three months. After the renovation, the concentration of suspended particles in the A-level area of the workshop was stabilized below 10 per cubic meter, the microbial concentration was 0CFU per cubic meter, and the pass rate of drug sterility inspection increased from 85% to 100%. Meanwhile, the replacement cycle of high-efficiency filters has been extended from three months to 18 months, reducing the annual equipment maintenance cost by 650,000 yuan and increasing production efficiency by 12%. ​
Vi. Summary
Against the backdrop of high-quality development in the pharmaceutical industry, the quality control standards for drug production are becoming increasingly strict. As a core link in quality assurance, the importance of air purification is becoming more and more prominent. Although medium-efficiency air filters are in the middle of the filtration system, they play a crucial role of “connecting the upper and lower levels” – they not only “relay” the primary filtration but also “reduce the burden” for the high-efficiency filtration. By precisely removing air pollutants, they provide a stable and clean environmental foundation for pharmaceutical production. ​
Pharmaceutical enterprises need to fully recognize the application value of medium-efficiency air filters, scientifically select and maintain them in a standardized manner based on their own production needs, and incorporate them into the entire process system of drug quality control. In the future, with the continuous upgrading of filtration technology (such as the application of low-resistance and high-efficiency synthetic fiber filter materials and intelligent differential pressure monitoring systems), medium-efficiency air filters will play a greater role in ensuring drug quality, reducing production costs, and promoting the green development of the pharmaceutical industry.