Drug Excretion in Human milk

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Breast milk is the optimal source of nutrition for infants. The risk to the infant depends on the amount of drug bioavailable to the mother, the amount reaching breast milk and the actual amount of drug ingested and bioavailable to the nursing infant.

Mechanism of transfer from blood to milk

The basic mechanisms are the same as those across other biologic membranes.

• Diffusion of low molecular weight substances through small water- filled pores
• Diffusion of lipid soluble compounds through lipid membranes
• Active transport carrier-mediated

Factors affecting drug excretion in breast milk

The drug dose, route and frequency of administration and metabolism are important factors in determining the amount of drug available for excretion into milk.

Maternal parameters
• Drug dosage and duration of therapy
• Route and frequency of administration
• Drug metabolism and renal clearance
• Blood flow to the breasts
• pH of milk
• Milk composition
Drug parameters
• Oral bioavailability (to mother and infant)
• Molecular weight
• Lipid solubility
• Protein binding
Infant parameters
• Infant age
• Feeding pattern
• Amount of breast milk consumed
• Drug absorption, distribution, metabolism and elimination