The aging process also affects the role of drug-binding serum proteins. The total serum protein level is usually maintained (while albumin levels may diminish slightly, increasing levels of alpha 1 antitrypsin keeps the total protein level normal). More significantly, the affinity of the serum proteins for protein-bound drugs lessens as patients age. The degree of plasma protein binding has a significant impact on the pharmacologic activity of the drug, because it is the free drug that is physiologically active and exerts the pharmacologic effect.