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The Art of Precision Measurement – Novasina APPLICATION NOTE

Novasina의 'The Art of Precision Measurement – Novasina APPLICATION NOTE'에 관한 응용자료의 주요 내용은 다음과 같다.

PHARMACEUTI-CAL TRENDS: WATER ACTIVITY MEASUREMENT
Water activity has been broadly used in the pharma-ceutical industry since the publication in 2006 of USP <1112>, an informational chapter on the application of water activity in pharma. 
While <1112> provided guidance for the utilization of water activity, it was not an official method. Now USP has developed USP <922> Water Activity as an official method which will hope-fully further facilitate its implementation as an integral part of a pharmaceutical quality program. Potential applications for water activity in pharmaceuticals include stability control, microbial risk pre-vention, optimized formulation, reduced caking and clumping, and moisture migration control. The resulting key benefits of these applications are higher quality pro-duction output, greater consumer satisfaction and con-fidence, and less product waste and recalls. Clearly, water activity is a powerful and often essential quality parameter for pharmaceutical products.

LabMaster aw-neo Most reliable water activity meter on the market


USP <922> WATER ACTIVITY METHOD
Recommendations for the determination of water activity are outlined in USP <922> Water Activity. This method becomes official in May 2021 and provides guidance for water activity measurement. 
It includes a brief theoretical background explanation and discusses some factors that influence water activity including solute concentration and uploaderature.
Sensor types and calibration: USP <922> also provides a short review of the various sensor types available for mea-suring water activity and highlights the strengths of each. It provides guidance on the qualification of instruments with water activity instruments classified as Group B inst-ruments. It highlights that water activity meters should be calibrated using standard solutions and this should be done at a minimum yearly or whenever a calibration check fails. Calibration verification checks should be conducted daily based on the instructions from the instrument manufactu-rer and using a minimum of two standards that book-end the typical water activity range. The number of replicates used for a calibration check should match the number of replicates used for sample testing.

Sampling: For sampling, guidance is given to limit expo-sure f the sample to ambient conditions by using sealed containers 
with limited headspace. The transfer of samples from extreme uploaderatures is discouraged due to the poten-tial for condensation to form inside the containers. Water activity measurements should be conducted according to the manufacturer’s instructions and reported along with the uploaderature.


CRITICAL WATER ACTIVITY FOR CRYSTALLINE EXCIPIENTS
Excipients, among many functions, act as bulking agents and protect Active Pharmaceutical Ingredients(API) in pharmaceutical solid dosage products. Typically, the matrix of these excipients is either crystalline or amorphous.
For crystalline excipients, the addition or loss of waters of hydration or deli-quescence can result in undesirable changes in product quality such as modification of dissolution properties or reduction in the efficacy of the API. These change processes are thermodynamically controlled and, therefore, are related to water activity. 
The moisture sorption isotherm, which describes the relationship of moisture content to water activity, will clearly show the 
deliquescence of the crystal-line material by a sharp 90 degree turn in the isotherm(Figure 1) (2). The water activity where these changes occur is called “critical water activity.” The key to avoiding problems with a crystalline excipient is to specify that the water activity be in a safe range based on the critical water activities identified through the moisture sorption iso-therm. Any incoming excipient supplies should then be monitored for water activity to ensure that this specification is being met.

Figure 1. Moisture sorption isotherm showing the deliquescence of a crystalline material (3).


CRITICAL WATER ACTIVITY FOR CRYSTALLINE EXCIPIENTS
Amorphous excipients are typically low-moisture and are in a meta-stable glassy state. Their ability to provide protection to the API depends on them remaining in the glassy state throughout the life of the product. A transition of the excipient matrix from the glassy state to the rubbery state, called a “glass transition,” will result in structural collapse, increased mobility, changes in dissolution, and increased susceptibility to caking and crystallization (4). Consequently, the product will not flow, compress, or tablet properly, and dissolution may occur prematurely. A glass transition can be induced through either a change in uploaderature or a change in water activity. The water activity where a glass transition occurs for a product is called the “critical water activity” and can be identified as a sharp inflection in the moisture sorption isotherm (Figure 2) (5). To maintain the functionality of amorphous excipients, it is important to determine its critical water activity and take measures to ensure that the water activity of the product remains below that critical water activity throughout the life of the product.


Figure 2. Moisture sorption isotherm indicating the critical water activity for a glass transition. Below the critical water activity, the product remains stable. Above the critical water activity, the product becomes unstable and shelf life is reduced (5).

THE MOST IMPORTANT SPECIFICATION
Water activity is sometimes an over-looked and underestimated parameter in pharma quality and formulation. Ho-wever, it 
offers critical information for optimizing product stability. Issues with deliquescence, caking and clumping, dissolution, microbial susceptibility, API degradation etc. can be resolved by identifying the ideal water activity range for the product and implemen-ting water activity measurement as a routine parameter for batch release. With the water activity at this ideal range, most pharmaceutical products will also qualify for reduced microbial limits testing, resulting in time savings and reducing production costs.

Novasina의 'The Art of Precision Measurement – Novasina APPLICATION NOTE'에 관한 궁금한 내용은 본 원고자료를 제공한 DKSH 코리아(주)를 통하여 확인할 수 있다.

Reference(참고문헌): DKSH application note

Model Name(모델명): Labmaser aw-neo
The Person in Charge(담당자): Kim Nakhyeon
Maker(제조사): Novasina
Country of Origin(원산지): Switzerland
Mail inquiry: dksh.info.tec@dksh.com
Data Services(자료제공): DKSH Korea

<이 기사는 사이언스21 매거진 2022년 3월호에 게재 되었습니다.>

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