The choice of the process to be used for the extraction of a drug depends on a number of factors.

Nature of the Crude Drug

The choice to use maceration or percolation primarily depends upon the nature and characteristics of the crude drugs to be extracted. Therefore, knowledge of the type of organs and tissues of the plant matter is essential for achieving the best result.

Stability of the Crude Drug

Continuous hot extraction procedures should be avoided when constituents of the drug are thermolabile.

Cost of the Crude Drug

When the crude drug is expensive (e.g. ginger), it is desirable to obtain complete extraction. Therefore, from the economic point of view, percolation should be used. For inexpensive drugs, maceration, despite its lower efficiency, is acceptable in view of its lower cost.

Solvent

Selection of the solvent depends on the solubility of the desired components of the material. If the constituents demand a solvent other than a pure boiling solvent or an azeotrope, continuous extraction should be used.

Concentration of the Product

Dilute products such as tinctures can be made by maceration or percolation. For semi-concentrated preparations, the more efficient percolation process is used. Concentrated preparations, such as liquid or dry extracts, are made by percolation.

Recovery of Solvent

Solvent is preferably recovered under reduced pressure to save thermolabile constituents.