How does protein binding affect the availability of warfarin when taken with aspirin?

Protein binding affects the availability of warfarin when taken with aspirin because aspirin can displace warfarin from its protein binding sites. This displacement increases the amount of free (active) warfarin in the plasma, which can enhance its anticoagulant effect and potentially lead to toxicity.

When warfarin and aspirin are taken together, aspirin binds more strongly to the same protein sites as warfarin. As a result, aspirin displaces warfarin, leading to a higher concentration of free warfarin in the bloodstream. Since warfarin is only therapeutically active in its free form, this interaction effectively increases the dose of warfarin, which can be dangerous due to its potential toxicity.