What factor most influences drug excretion during lactation?

The key factor influencing drug excretion during lactation is maternal kidney function and the pH of breast milk. The kidneys play a critical role in the elimination of many substances from the body, including medications. If maternal kidney function is impaired, the clearance of drugs may be reduced, resulting in higher concentrations in the bloodstream and potentially in breast milk.

Additionally, the pH of breast milk can affect the ionization of certain drugs. Many drugs exist in both ionized and non-ionized forms; the non-ionized form is more likely to pass through biological membranes and enter breast milk. The slightly acidic pH of breast milk can lead to alterations in the solubility and absorption of various medications. Thus, both the efficiency of renal clearance and the characteristics of breast milk directly impact the extent to which drugs are excreted into breast milk, emphasizing their significance in the context of lactation and pharmacological safety for nursing infants.