The passage of a chemical or drug across the tissue of the gastrointestinal tract into the bloodstream that goes to the liver, where it may undergo metabolism before entry into the general circulation of the bloodstream.

Bioavailability

The extent to which a chemical or drug crosses the tissue of the gastrointestinal tract and through the liver, and enters the general circulation of the bloodstream either as active drug or metabolite(s).

Colostrum

Breast fluid that is secreted during the first few days after birth, before the onset of mature milk.

Concentration

The amount of a substance in a given volume of body fluid. The same as Level.

Ductus Arteriosus

A blood vessel that connects the left pulmonary artery and the aorta of the fetus.

Exclusive Breastfeeding

Feeding an infant with breastmilk alone, with no other intake whatsoever. According to the American Academy of Pediatrics and the World Health Organization, breastfeeding should be exclusive breastfeeding for the first six months of the baby's life.

Excretion

The elimination of a chemical or drug from the body, either as unchanged drug or its metabolite(s), usually by the kidneys.

Expressed Milk

Milk that is extracted from the breast by means other than nursing, such as by hand or using a breast pump.

Foremilk

The first milk that is excreted from the breast at the beginning of a nursing bout or at the beginning of expression. It is relatively low in fat.

Galactorrhea

Abnormal production of milk in nonpregnant, nonlactating women or in men.

Gram (g)

A unit of weight equal to about one-thirtieth of an ounce.

Half-life

The time required for one-half of the total concentration of a chemical or drug in a body fluid, usually the general bloodstream, to be eliminated. It takes two half-lives for 75% of a drug to be eliminated and 5 half-lives for 97% of a drug to be eliminated.

Hindmilk

The last milk that is excreted from the breast at the end of a nursing bout or at the end of expression. It is relatively high in fat.

Infant

A young child, from birth through one year of age.

In Utero

Within the uterus.

Kilogram (kg)

A unit of weight equal to 1,000 grams.

Lactation

The normal secretion of milk by the breast following pregnancy.

Level

The amount of a substance in a given volume of body fluid. The same as Concentration.

Liter (L)

A volume of liquid equal to about 1.05 quarts.

Metabolism

The process of the body's breaking down one chemical or drug into another. Metabolism changes a substance into active or inactive metabolite(s).

Metabolite

A chemical or drug that is formed by the actions of the body, usually the liver, on the parent compound. The metabolite may be inactive or have activity that is the same or different from the parent substance.

Microgram (mcg)

One-millionth of a gram.

Milligram (mg)

One-thousandth of a gram.

Milliliter (mL)

One-thousandth of a liter of liquid.

Neonate

An infant of 28 days of age or less. Same as a Newborn.

Newborn

An infant of 28 days of age or less. Same as a Neonate.

Parent compound

The original chemical or drug that is taken by the mother.

Peak

The highest concentration of a chemical, drug or metabolite within a body fluid.

Plasma

The fluid portion of the blood which contains no red or white blood cells.

Postpartum

The time right after delivery of an infant.

Prenatal

Before birth.

Preterm

Delivery of an infant prior to the 37th week of gestation.

Prodrug

A drug that is inactive when taken and then metabolized in the body to an active drug.

Prolactin

A hormone produced by the pituitary gland that stimulates milk production.

Serum

The clear fluid portion of the blood which contains no red or white blood cells or blood platelets.

Steady-state

The time at which the concentration of a substance remains constant (such as in blood), because the rate of drug administration equals the rate of drug elimination from the body.

Trough

The lowest concentration of a chemical, drug or metabolite within in a body fluid.

Weight-adjusted Dosage

The dosage of a drug divided by the weight of the individual.