Drugs in breast milk.

Abstract

The amount of drug excreted into breast milk is dependent upon the lipid solubility of the medication, the mechanism of transport, the degree of ionization, and change in plasma pH. The higher the lipid solubility, the greater the concentration in human milk. The majority of drugs are transported into mammary blood capillaries by passive diffusion. The rest are transported by reverse pinocytosis. Once the drug has entered the epithelial cells of breast tissue, the drug molecules are excreted into the human milk by active transport, passive diffusion, or apocrine secretion. The amount of free (active) drug available for transport depends on the degree of protein binding the plasma pH. Another factor affecting excretion of drugs is the time when breast feeding occurs. In the 1st few days of life, when colostrum is present, water-soluble drugs pass through the breast more easily than afterwards when milk is produced. Then lipid-soluble drugs cross in higher concentrations. The effect on nursing infants is dependent on the amount excreted into the milk, the total amount absorbed by the infant, and the toxicity of the drug. The use of the following drugs in breast feeding mothers is reviewed: anticoagulants, antihypertensives and diuretics, antimicrobials, drugs affecting the central nervous system (alcohol, chloral hydrate, meprobamate, lithium, and aspirin), marijuana, other drugs (antihistamines, atropine, ergot alkaloids, laxatives, nicotine, iodides, propylthiouracil, theophylline), hormones (insulin, thyroxine, and oral contraceptives), and radiopharmaceuticals.