What is the impact of protein binding on drug distribution?

Protein binding significantly affects drug distribution by limiting the amount of free drug available in the systemic circulation. When drugs are bound to plasma proteins, they are typically inactive in terms of pharmacological action because only the unbound portion can interact with target receptors or exert effects at the cellular level.

As a result, drugs that are highly protein-bound tend to have a decreased volume of distribution. This is because less of the drug is available to permeate tissues and reach the site of action. Consequently, the therapeutic effects can be prolonged, as the bound drug acts as a reservoir, slowly releasing free drug into circulation over time. This prolongation of action occurs since the drug remains in the body longer, facilitating a sustained pharmacological effect without immediate rapid clearance.

Contrastingly, drugs that are not significantly protein-bound can distribute more freely into various tissues, leading to potentially quicker onset and shorter duration of action. Therefore, when considering pharmacokinetics, protein binding is a critical factor influencing both drug distribution and the duration of pharmacological effects.