Compatibility studies using thermal analytical techniques

Compatibility studies using thermal analytical techniques 

The use of DSC or DTA in compatibility testing is, or should be, falling out of favour. The concept of any stress test is that a formulation may be stored in conditions that stress the sample and subject it to a likelihood of accelerated decomposition. DSC or DTA have been used, occasionally to examine the final formulation but more usually to examine incompatibility between any two ingredients in a formulation. Thus, in its simplest terms the drug and a chosen excipient are scanned individually from ambient through their dehydration, melting or decomposition events. Then the materials are scanned as their 1 1 physical mix. The stress is thus provided by an increase in scanning temperature and no contribution of, for instance, humidity to instability can be assessed. 

The choice of a 1 1 mixture is dubious. Originally intended to maximise the detection of incompatibility between two ingredients, it does not represent the compositions or ratios found in the final formulation. A particular example of 

In conclusion the technique gives ambiguous data that may indicate that interactions and or incompatibility occur. The techniques over-estimate the risk of this incompatibility. 

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Compatibility studies using thermal analytical techniques... 

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