Pharmaceutical tinctures are alcoholic solutions prepared by maceration, digestion, or percolation. The term tincture is also occasionally used for preparations based on glycerin or vinegar. Ethanol offers the advantage of dissolving constituents that are insoluble or sparingly soluble in water while helping to preserve them in solution. A water-alcohol menstruum can extract a larger proportion of active principles of most plants than can water alone, but at the same time contains sufficient alcohol to prevent decomposition.
The proportion of drugs represented in the different kinds of tinctures is not uniform, but varies according to the established standards for each. Tinctures of potent drugs represent the activity of 10 gm. of a drug of minimum strength, in each 100 cc. of tincture. When drugs having a higher potency, than the minimum, are used in preparing tinctures the finished product is assayed and adjusted to the uniform strength. This conforms in principle to the recommendation of the International Protocol as adopted at Brussels, and with international standards. There are two important variables in tinctures: the concentration of the herb and the strength of the alcohol.
Concentration of Herb - The amount of herb in a given amount of menstruum defines the concentration of the extract. Most tinctures are in concentrations of 1:4 or 1:5. In the examples just given, the first number represents the weight of the herb and the second represents the volume of menstruum, so they express a ratio of weight to volume (w:v).
There are a number of ways to express concentrations. The expression percent may be used, according to circumstances, with one of four different meanings. In order that the meaning attached to the expression in each instance is clear, the following notations are used.
- Percent w/w (weight to weight): number of grams of active substance in 100 g of product
- Percent w/v (weight to volume): number of grams of active substance in 100 ml of product
- Percent v/w (volume to weight): number of milliliters of active substance in 100 g of product.
Strength of Alcohol - Alcohol can be used in concentrations of 45%, 60%, 70%, and 90%. In pharmacy, the expression "70% ethanol" describes a solution made up of 70 parts of 96.4% ethanol and 30 parts of water. As an example, "Tinctura calarni 1:5-70%" means that this tincture of Acorus calamus root was made by macerating 1 part of root (in weight) in 5 parts (by volume) of a 70% ethanol solution. The so-called mother tinctures used in homeopathy as the starting point for potentiation are usually prepared by bruising the fresh herb, expressing the juice, and adding 96% alcohol to the juice in an amount equal to one-third or one-half the volume of the fresh juice.