epitope A molecular region on the surface of an antigen that elicits an immune response and can combine with the specific antibody produced by such a response; also called a determinant or an antigenic determinant.

equivalence Two lots of product are equivalent if, within experimental error, they are essentially equal in purity/impurity, potency, identity, and safety. A more stringent requirement than comparability. (See comparable)

Escherichia coli Bacteria normally found in the intestinal tract and widely used in biochemical and genetic studies and genetic engineering. E. coli is often used as a vehicle for combining a segment of DNA with an unrelated segment, creating continuous DNA that does not occur naturally (recombinant DNA).

exception A deviation from approved GMP procedure; an out-of-specifications result or unexpected or out of trend result; a customer complaint. Exceptions must be detected, investigated, and managed using quality systems such as CAPA (corrective and preventive action).

excipient A type of raw material that is present in the drug product and thus has direct patient contact; includes inert materials such as bulking agents, stabilizing agents, preservatives, salts, solvents, or waters. An excipient must be evaluated for safety in animals, unless it has been approved as GRAS or is on a list of approved excipients.

exclusion limit In size-exclusion (or gel filtration) chromatography, the smallest size or dimension of molecule that is too large to enter the pores on gel particles.

exogenous Developing from outside, originating externally. Exogenous factors can be external factors such as food and light that affect an organism.

express To translate a cell's genetic information, stored in its DNA (gene), into a specific protein.

expression system A host organism combined with a genetic vector (such as a virus or circular DNA molecule called a plasmid) that is loaded with a gene of interest. The expression system provides the genetic context in which a gene will function in the cell—that is, the gene will be expressed as a protein.

expression vector A virus, plasmid, cosmid, or artificial chromosome that delivers foreign genes to a host, creating a recombinant organism that will express the desired protein.

extractables 1. Substances withdrawn (such as the medicinally active components of plant or animal tissue) by a physical or chemical process. 2. Materials that are actually removed from a container or closure by a given formulation or product. (See leachables)

extraction Liquid-liquid extraction is a process in which a solute is removed from a liquid by transferring the solute into a second liquid phase. The two liquid phases must be insoluble with each other. Separation is based on different solubilities of the solute in the two phases. Extraction is gentle and suitable for unstable molecules.

extrusion A process of forming rods, tubes, or other continuously formed pieces by pushing hot or cold semisoft solid material through a die; also any process of pushing a substance through holes or a tube.