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Medicinal Sprays: How Do You Test For "Stickiness?"

By Eric Chiang and By Robert G. McGregor, Brookfield Engineering Laboratories, Inc.

Robert G. McGregor, General Manager
Eric Chiang, Product Manager, Texture Analyzers

Medicinal and pharmaceutical products that are applied by spraying have gained in popularity because they easily coat the targeted surface without need for further spreading action by the consumer. Oral and nasal sprays may actually work with greater rapidity, migrating quickly to the target area and producing a very desirable benefit for the patient in terms of faster relief. How do manufacturers know whether the spray will actually stick to the targeted surface once it arrives? Relying on feedback from user groups is one way to get the necessary information, but would seem to have a highly variable range of responses since it is based on human judgment.

Instruments known as Texture Analyzers or Texture Testers provide a convenient and objective means for making this measurement. See Figure 1. These devices can run a test within a matter of seconds to determine the “stickiness of sprays. They are simple to operate and give “tighter” objective results compared to human sensory panels. Compared to many other types of instruments found in pharmaceutical labs, Texture Analyzers are easily affordable and do not require complicated procedures for calibration or maintenance. In fact, test technicians are making measurements within a matter of minutes when first using the instrument.

Choices involved in selecting the correct piece of equipment boil down to load cell range and type of measurement probe. With a load cell that has capacity up to 1000 grams and a cylindrical probe of 1-inch diameter, the Texture Analyzer, when used in a QC lab, has the ability to make measurements in standalone mode that will satisfy most spray applications. During initial evaluation in R&D, use of software to run the Texture Analyzer may be desirable so that different spray formulations can be easily compared against one another.