Ideal indicator is one which would permit the following statement to be printed on the phial. "If this spot has turned red (or any other colour) DO NOT USE THIS".
Broadly, indicators can be of the following types:
- GO-NO-GO without delay
- GO-NO-GO with required delay
- Time/Temperature indicator
- Real-Time recorder
- Multi-Temperature GO/NO GO
- Multi-Temperature with time element
End-use requirement of indicator also affects the choice of performance characteristics required. For example, if an indicator to be fixed on the phile, is being used as a decision making tool.
In this case the indicator change, must correspond very closely to the temperature and time at which product change is anticipated.
Closeness of product and indicator change leads to the problems of false positive and false negative indication. If the indicator were to change, but the anticipated change in product has not taken place, it would have given a false positive and good product would be discarded. Conversely, if the indicator did not change but the product did change, it would be a false negative and bad product would be retained.
In order to use an indicator as a decision making tool, it is important to identify the parameters of product which the indicator should measure and then carefully consider the false positive and negative indications that are likely to occur. An indicator may also be used a as monitoring tool only. For example, the retail outlets could be instructed to look inside all especially marked cases of drugs being received from manufacturers / stockiest to find "Proper shipment Indicators" where indication are to be recorded to initiate necessary action for improvement of shipment condition.