The Pharmaceutics and Compounding Laboratory
Pharmaceutical Solutions II:
Nonaqueous Solutions


Tinctures are alcoholic or hydroalcoholic solutions prepared from vegetable or chemical substances. The concentration of solute varies up to 50%, e.g. Vanilla Tincture USP, Iodine Tincture USP. Tinctures are alcoholic solutions of nonvolatile substances which are generally extracted by maceration or percolation. Tinctures of potent drugs represent the activity of 10 g of the drug in each 100 ml of the tincture; they are 10% tinctures. With a few exceptions, nonpotent tinctures represent 20 g of the drug per 100 ml of tincture.

Tinctures are prepared chiefly by percolation and maceration. Percolation is the procedure of choice when the crude drugs are cellular in structure; plant exudates tend to become impacted in the percolator and stop the flow so that maceration is preferred in such preparations. Moderately coarse powders are preferred, because coarse powders are slowly penetrated by the menstruum and fine powders tend to clog the percolator.

Usually alcohol or a hydroalcoholic menstruum is employed. The choice of menstruum depends on the solubility, stability, and ease of removal of the desired constituent. Other inactive constituents are extracted, but if the material is not objectionable, it is allowed to remain.

In the process of percolation, the drug is dampened with the menstruum and allowed to stand for a short period before packing the percolator so that the drug may expand as the menstruum is absorbed. If the drug is packed into the percolator and moistened, the swelling would pack the drug so firmly that the percolate could not flow.

The menstruum is then added to cover the drug and the lower opening is closed when the liquid is about to drip from the percolator. This permits the air between the particles to escape as the menstruum descends. Maceration for a prescribed time permits saturation of the menstruum in contact with the drug, assuring a more nearly complete extraction.

The menstruum is then allowed to flow or percolate at a definite rate. Normally the percolate collected is assayed before final volume is reached, and then it is adjusted to the proper strength.

In the process of maceration the drug is soaked with the menstruum in a closed container. The closed container prevents the loss of volatile constituents and evaporation of the menstruum. The mixture is agitated frequently so the menstruum at the bottom of the container does not become saturated and incapable of extracting further drug. Circulatory maceration is an efficient modification which eliminates the need for agitation. When heat is employed in maceration, the process is known as digestion. The mixture is then transferred to a filter, and the residue is washed with sufficient menstruum to bring the tincture to final volume.