RLO: Plasma Proteins and Drug Distribution


What is the effect of protein binding on drug action?

For a drug showing little protein binding, the plasma acts simply as a watery solution in which the drug is dissolved. Where protein binding does occur the behaviour of the drug may be influenced in several ways:

1. Extensive plasma protein binding will increase the amount of drug that has to be absorbed before effective therapeutic levels of unbound drug are reached. For example, acidic dugs (such as acetyl salicylic acid – aspirin) are often substantially bound to albumin.

2. Elimination of a highly bound drug may be delayed. Since the concentration of free drug is low, drug elimination by metabolism and excretion may be delayed. This effect is responsible for prolonging the effect of the drug digoxin. (more...)