EXPRESSION OF ACTIVE INGREDIENT CONTENT OF MEDICINES

Frequently, for reasons related to stability, taste or solubility, the base form of a drug is administered in an altered form, such as an ester or salt. This modified form usually has a different molecular weight.

For example, caffeine citrate:

There are therefore two ways to express the active ingredient content of a medicine: either based on the salts contained in the formulation (e.g., 20 mg of caffeine citrate in this case) or based on the base equivalent that contributes to the pharmacological activity of the medicine (e.g., 10 mg of caffeine base).

In English-speaking countries, the content is typically expressed as salt, while in French-speaking countries, it is usually expressed as base. Unfortunately, there is no international standard for this, leading to frequent confusion between the two methods. As a result, it is not unusual for drugs labelled as bases to be used in protocols that express them as salts, and vice versa.

For salts where the non-active part is relatively small compared to the active part, these confusions often result in negligible errors. However, with small active molecules combined with heavy salts (such as phosphates, sulphates, carbonates, citrates, fumarates, etc.), the non-active part can constitute more than half of the molecular weight. In such case, confusions can lead to underdosage (resulting in ineffective treatment or a risk of resistance) or overdosage (increasing the risk of adverse effects). Examples of such products include caffeine citrate solution for injection and chloroquine phosphate tablets.