[e-drug] Study of stability of medicines under tropical conditions (3)

["Magnus Ajong" <magnusajong@yahoo.com>]

E-DRUG: Study of stability of medicines under tropical conditions (3)
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Dear Dr Paul Newton,
   
Studies on the stability of medicines under different storage conditions require careful planning from the beginning. You would not want to end your experiments halfway or be unable to perform additional experiments because insufficient samples were stored from time zero. Here are some of the factors our laboratory would consider in selecting the original number of samples to be put in stability:
- # of stability cdtns (e.g 25, 30 and 40 degrees celcius)
- # of time pts (e.g 0, 2 wks, 1 mth, 3 mth, 6 mth, 1 yr...)
- # of variables (e.g active ingredient, dissolution, preservative, degradation ...)
- # of batches
- # of samples per batch (usually 3)
- # injections on HPLC (if preferred method of analysis) per sample usually 3)
- ...
   
This number will also depend on how your sample preparation will be done. From each batch a number of tablets e.g 10 can be crushed together, from which 3 separate samples are prepared (each equivalent to mean wt of total tabs). This method gives you a more homogenous sample, however some active ingredient can be lost in the process e.g sticking to mortar bottom. Alternatively, from each batch the uniformity of mass test can be performed on the tablets. If it meets the requirements then individual tablets can be prepared as samples. Tablets will easily disintegrate in most solvents with slight shaking. 
   
As you suggested, the ICH does not specify how the degration studies should be conducted and as the inherent degradation products of your samples are unknown, I will suggest you store extra samples for each time point for reasons mentioned in the ICH and in this text.
   
Hope this helps.
   
Magnus A. Atemnkeng PhD
Montreal, Canada
E-mail: magnusajong@yahoo.com