Trouble-shooting parenterals via particle identification
Identification of visible product particles, like protein aggregates, can form the foundation of an effective, in-process contamination control program
BY DR. OLIVER K. VALET
Parenterals are subject to high requirements in regards to purity. These solutions are regulated by United States Pharmacopoeia (USP) and have to be free of any visible particles (less than 50 µm). The limit values for non-visible particles are to be followed, while intense efforts in production and quality assurance are required to ensure that they are.
Depending on the process, 0.2 to 3.0 percent of waste due to particles is accrued. If the cost of waste exceeds a significant amount, the source of the impurification certainly needs to be sought. The simple identification of the particles facilitates the detection and elimination of the source; and, in turn, the cost of this waste and the empirical attempts to solve the problem are reduced.
Simple contamination information
A system has been developed for the automatic chemical analysis of particles on the basis of RAMAN spectroscopy.1 The measuring device identifies all particles of organic and inorganic nature larger than 2 µm.
The key design piece that makes this possible is the metalized polymer membrane (below) through which the product is passed. The size of the nuclear pore is based on the solution's viscosity and size of the particles to be examined. The contrast between particles and membrane is optimized for particle recognition through automatic image analysis.
The membrane, once coated with particles, can be analyzed using a Liquid Particle Explorer, which was developed for the identification of particles according to the standards of measuring devices in a cGMP-controlled surrounding.2
Similar to the method of membrane evaluation described in the USP, microscopic images (below) of the entire membrane surface covered with particles are automatically recorded and evaluated.1
The position, length and width of the particles is determined exactly, to the micrometer. The device carries out RAMAN spectroscopic examinations on the particles, and resulting spectra are automatically identified on the basis of the pharmaceutical and customer-specific database.
The database was created with RAMAN spectra of material samples. The system can, therefore, also clearly recognize mixtures of materials, such as rubber stoppers or dyed polymers, due to their characteristic spectra. An automatically created report provides the size, identification and spectrum quality as well as the result for each individual particle.
Particle sources at the production level
The search for the source of the impurification begins when a process exceeds the specification of the acceptance quality level. Currently, most end users responsible for production rely on their experiences. They have known their process for years and can, therefore, eliminate the contaminating source with a few trials and errors. For example, filter candles are replaced or stoppers are checked in regards to their particle load. This method may suffice; however, it often takes days, and some errors can't be contained and may disappear after some time.
Only a full analysis can provide information on the effect of the measures. External laboratories are rarely consulted due to the long time period between test and result, and because of the small statistical relevancy of a particle's single spectroscopic examination.
Identification of foreign particles from parenteral solutions supplies direct information regarding the impurification source.3, 4 Different sources during the production process are all considered—personnel, clothing, containers and caps. The established database contains 500 RAMAN spectra of substances, and end users may add new material samples to the database within minutes.
Examinations completed with the Liquid Particle Explorer enable a statistically relevant and comparable conclusion about the particles' chemical composition in a relatively short time. The main impurification sources can be detected on the basis of the particle spectrum of a product sample.
Resulting table of parenteral solutions, main source PVDF, and historical particle spectrum.
Figures 1 and 2 show the results of the measurements of a product of two different batches. The main contamination source of batch A is polyvinylidenfluoride (PVDF). In a secondary database, PVDF was identified as part of the membrane of a candle filter. A significant increase of the yield was achieved through the removal of the candle filter (a typical sample is shown in Figure 2).
Continous identification = clean intellingence
Continuous monitoring of particle composition is preventative quality assurance which, in turn, increases product safety.
To guarantee permanent protection, additional samples and rejects of this product and current batches were continuously examined. In the beginning, less noticeable impurification sources were detected and minimized.
Subsequently, some particles remained in the non-visible area and were assigned to this process. The specification of the product was extended through the historical as well as through the product- and process-specific particle ID distribution.
Deviations from the historical particle profile can, therefore, be quickly detected. Total particle load count can be constant using a particle counter, but the composition of the particles may vary significantly. The identification of a new particle type makes latent impurification sources visible before the damage is done.
The FDA also recommends characterization of foreign particles for the rapidly growing number of inhalers. Analysis of the particle composition can prove that no contaminating particles are present in these products.
Another application field is the analysis of particular drug delivery systems. For quality assurance purposes, analysis of the particles' material composition is exact to less than a micrometer and provides exact information about the particles and the production processes.
The synthetic membrane with nuclear pores, ranging from 0.2 to 8 ??m, is metalized and set in aluminum.
Based on determination of layerthikness parameters, release time of the active substances are reliably determined. Further, RAMAN examinations provide reliable information about the potency of such samples, especially after calibration to the active substance.
Effective downtime reduction
Through the statistically relevant result of particle measurements, the main impurification sources can be reliably detected within minutes. The source can then be removed quickly through cooperation between the quality assurance and production departments.
Liquid Particle Explorer technology can be used directly in production, reducing the time required for transport of samples and subsequent results. Establishing a customer-specific, secondary database will quickly provide information about the materials used in the process.
Microscopic images of the membrane with particles (white); below, the same picture after image recognition.
After the result of the identification (for example, of 50 particles, > 25 µm of blue polypropylene), only the blue screw caps made of this material are considered. Even if the result during the detection of cellulose fibers points to several sources—such as paper, cardboard and wipes—the number of possibilities is drastically reduced.
Through continuous monitoring of particle composition, latent particle sources can be detected before serious damage occurs, increasing product safety and reducing the number of batches restricted for approval.
This process is especially profitable for the production of drugs made of valuable active substances that can only be processed with great difficulty. In the long run, each particle-sensitive production profits from monitoring the particle identification.
The execution of particle composition measurements provides the drug manufacturer with a good starting basis for discussions with the authorities. Additional examinations of the particle composition are not mandatory, but authorities honor the fact that the manufacturer is seriously interested in an explanation of an occurred "out of specification" and has taken the appropriate initiative.
The secure identification of visible product particles, like protein aggregates, can form the foundation for the release of a rejected batch as deviation report. High values can be released directly and, therefore, reduce costs.
DR. OLIVER K. VALET is senior scientist at rap.ID Particle Systems, Berlin, Germany. Dr. Valet can be reached at: firstname.lastname@example.org
 O.Valet, Woher stammen Partikel, Reinraumtechnik, GIT-Verlag, 2001
 O. Valet, Schnelle Materialbestimmung von Mikropartikeln, Laborzeitschrift, GIT-Verlag, 2001
 O. Valet, "Made to Measure," Cleanroom Technology, Polygon Media, Sep 2002
 M. Lankers, "Determining particle composition: Consider the path to the source," CleanRooms, PennWell, July 2002