Moisture can be detrimental to drug product shelf-life. Peter Moir, Relequa Analytical Systems, describes how moisture profiling via the Equilibrium Relative Humidity can highlight moisture problems in drug materials.
The importance of Equilibrium Relative Humidity (ERH), alternatively known as Water Activity, in the food industry for shelf-life determination is well documented.1 The exposure of pharmaceutical products to moisture and the subsequent effect on the chemical or physical stability of moisture-sensitive products can have serious implications during manufacture and for shelf-life.
The interaction of pharmaceutical products with environmental moisture is governed by the same factors as for any moisture-sensitive material. Water molecules are readily absorbed or lost until an equilibrium – the material’s ERH – is reached; this can be measured by the relative humidity of the surrounding air. This methodology is more widely accepted for microbiological control of pharma products and is the subject of a chapter in the USP <1112> “Application of Water Activity Determination to Nonsterile Pharmaceutical Products”.
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