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Moisture content in tablets

Q: I wish to find out how moisture content in granules can affect the physical parameter of an uncoated tablet.

A: Fred Rowley responds:

Moisture is almost always present in a tablet. Even if you mix a nominal quantity of a minimum number of excipients in a dry blend with a small quantity of a single active, you still have some moisture. Moisture, then, is not an issue in and of itself.

Too much moisture will result in one set of problems (sticking, picking, microbial growth, stability issues) while too little will result in a different set of problems (lamination). The key question is: What is an appropriate specification for unbound moisture in a tablet?

There is no single answer. If you surveyed 100 different pharmaceutical tablet formulation specifications, you would perhaps see a mean specification range of 0.5-4.0%. As a guideline for consideration, the smaller the tablet, the lower the quantity of moisture necessary for a successful tablet. But even this rule of thumb has many exceptions.

Bottom line: You need moisture, but not too much. There is no magic number for all cases.