Which laboratory result can affect drug distribution and influence drug-to-drug interactions?

• A. Elevated BUN.
• B. Low serum albumin levels.
• C. Reduced glomerular filtration rate.
• D. Elevated creatinine levels.

Answer: (B)

Protein binding in the blood controls how drugs distribute and how interactions occur. Many medications attach to albumin; only the free portion can move into tissues, produce effects, or be cleared from the body. When albumin levels are low, a larger fraction of the drug remains unbound, raising the active plasma concentration. This not only changes distribution but also increases the risk that another drug will displace the bound drug from its albumin sites, further boosting free drug levels and the potential for toxicity or enhanced effects. This scenario is common in older adults due to malnutrition, liver disease, or chronic inflammation, making monitoring for interactions especially important. In contrast, signals like elevated BUN, elevated creatinine, or reduced glomerular filtration rate mainly reflect kidney function and influence elimination more than distribution.