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   Part 1

   Objective
   Methodology
   Introduction
   Part 2
   Conclusions

The GHP in its methods 2 and 3 uses the moisture (H) as unit of drug strength (UDS) in order to calculate the amount of alcohol necessary to prepare the MT.

In method 2 we add one part of solvent for each part of moisture. So if the moisture has the value H, we must add H parts of solvent to obtain 2 H volumes of MT (although we should say aprox. 2 H, because of the substances soluble in water which are extracted during the preparation and which are not taken into account by the GHP). The drug strength (DS) is the fraction that indicates how much parts of the MT contain one unit of drug strength (UDS).

Since each UDS is contained is 2 parts of MT, the DS of this method is 1/2.

The WSP considers as UDS, not the moisture of the plant, but the juice. Therefore in method 2 we must add one part of solvent for each part of juice, and using a similar reasoning that each UDS is contained in 2 parts of MT, the DS of this MT is also 1/2.

Now when we have a MT prepared following the GHP, seen form the point of view of the WSP, we have a DS related to the juice (J), and therefore we must express this DS as parts of MT which contain one part of juice (J), while we consider to have a final volume of

In this case each UDS is contained in x parts of MT, and the DS from the point of view of the WSP is 1/x. Since x is always smaller than 2, 1/x will always be greater than 1/2 which shows that the MT prepared following the GHP, but seen from the point of view of the WSP will always be more concentrated. This difference will be larger as the DR of the juice is higher.

Lets give an example. Suppose we have a plant with 70% of moisture (H) and 10% of dry residue (DR). We prepare two MT following method 2 of each pharmacopoeia. Then to prepare our first potency by WSP, we take 2 parts of the MT for each part of juice we need and proceed to add solvent up to 10 or 100 parts (for the decimal or centesimal scale resp.) Now, if we use the MT prepared by the GHP, and if we want to obtain the same concentration for our first potency, we should take the same amount of juice (which corresponds to 1 part of UDS) and which is contained in x parts of MT.

However the DS given in both pharmacopoeias is the same, and in theory we should also have taken 2 parts.

The percentual difference (d%) can be calculated based on the quantity we should use to have first potencies with the same concentration, and the quantity we normally take following the DS of the pharmacopoeia we use.

To obtain a general formula we can state that

theorical part we should use to obtain equal concentration

parts we really use following the pharmacopoeia

difference in absolute value (=d)

if then

Comparing the 2 pharmacopoeias in method 2 we can replace by x' (=2) and by x , then we have:

Should we use a MT prepared by method 3 we have and then

We obtain exactly the same formula which proves that the difference is independent of the final weight or volume of the MT and solely depends on the UDS considered in each case.

This formula enables us to quantify the percentual difference between the quantity of MT we should use, and the one we really use to prepare our first potency according to the DS of each pharmacopoeia.