Quality control of pharmaceutical ingredients: developing a caking test for industry

Mark Leaper

Research output: Contribution to journalConference abstractpeer-review


Objectives - Powdered and granulated particulate materials make up most of the
ingredients of pharmaceuticals and are often at risk of undergoing unwanted
agglomeration, or caking, during transport or storage. This is particularly acute
when bulk powders are exposed to extreme swings in temperature and relative
humidity, which is now common as drugs are produced and administered in
increasingly hostile climates and are stored for longer periods of time prior to use. This study explores the possibility of using a uniaxial unconfined compression test to compare the strength of caked agglomerates exposed to different temperatures and relative humidities. This is part of a longer-term study to construct a protocol to predict the caking tendency of a new bulk material from individual particle properties. The main challenge is to develop techniques that provide repeatable results yet are presented simply enough to be useful to a wide range of industries.
Methods - Powdered sucrose, a major pharmaceutical ingredient, was poured
into a split die and exposed to high and low relative humidity cycles at room
temperature. The typical ranges were 20–30% for the lower value and 70–80% for
the higher value. The outer die casing was then removed and the resultant
agglomerate was subjected to an unconfined compression test using a plunger fitted to a Zwick compression tester. The force against displacement was logged so that the dynamics of failure as well as the failure load of the sample could be recorded. The experimental matrix included varying the number of cycles, the amount between the maximum and minimum relative humidity, the height and diameters of the samples, the number of cycles and the particle size.
Results - Trends showed that the tensile strength of the agglomerates increased
with the number of cycles and also with the more extreme swings in relative humidity. This agrees with previous work on alternative methods of measuring the tensile strength of sugar agglomerates formed from humidity cycling (Leaper et al 2003).
Conclusions - The results show that at the very least the uniaxial tester is a good
comparative tester to examine the caking tendency of powdered materials, with a
simple arrangement and operation that are compatible with the requirements of
industry. However, further work is required to continue to optimize the height/
diameter ratio during tests.
Original languageEnglish
Pages (from-to)A25
Number of pages1
JournalJournal of Pharmacy and Pharmacology
Issue numberS1
Publication statusPublished - Sept 2008
EventBritish Pharmaceutical Conference 2008 - Manchester , United Kingdom
Duration: 7 Sept 20089 Sept 2008


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