How does protein binding affect drug distribution?

Protein binding plays a crucial role in drug distribution within the body. When a drug binds to plasma proteins, such as albumin and globulins, it forms a protein-drug complex that is not readily available to exert its therapeutic effects. This binding reduces the concentration of free (unbound) drug in the bloodstream. Since only the free drug can cross cell membranes and interact with targets, a higher degree of protein binding can lead to a lower effective concentration of the drug available for therapeutic action, ultimately impacting its efficacy.

Additionally, drugs that are highly protein-bound are generally less susceptible to swift metabolism since only the unbound drug is available for biotransformation by liver enzymes. Consequently, the reduced free concentration can also influence the pharmacokinetic profiles, including the duration of action and clearance rates. Thus, choice C accurately captures the impact of protein binding on drug concentration, efficacy, and metabolic processes.