Drug Excretion: Pulmonary and Glandular Routes

Drugs are excreted through various unconventional routes, including the lungs, breast milk, and saliva.

In the lungs, volatile drugs diffuse into the exhaled air. Factors like drug solubility, pulmonary blood flow, and respiration rate influence pulmonary excretion.

Less blood-soluble gaseous anesthetics, like nitrous oxide, are rapidly excreted, whereas highly soluble compounds, like alcohol, are expelled more slowly.

Breast milk, being more acidic than plasma, facilitates the excretion of weakly basic drugs.

Notably, many nonelectrolytes like ethanol enter breast milk quickly, reaching concentrations similar to those in the plasma. So, overconsumption of such agents can negatively impact the suckling infant.

Next, nonionized lipid-soluble drugs can diffuse through the epithelial lining of the salivary glands, leading to the secretion of drug-containing saliva in the mouth.

Saliva's drug concentration closely mirrors the unbound drug concentration in plasma. So, it is a useful alternative for measuring drug concentrations, especially when obtaining blood samples is challenging.