Final answer:
The correct answer is a. increased risk of adverse effects, which occurs when two highly protein-bound drugs compete for the same binding sites, potentially increasing the levels of free drug and resulting in augmented pharmacological or toxicological effects.
Step-by-step explanation:
When two drugs that are both highly protein-bound are administered together, the correct answer is a. increased risk of adverse effects. This increased risk is due to the competition between the drugs for the same binding sites on plasma proteins such as albumin. Since drugs bind to these proteins in the bloodstream, high plasma protein binding (PPB) can affect both the distribution of the drugs to tissues and their subsequent clearance from the body. When two highly protein-bound drugs compete for binding, it can result in increased levels of 'free' or unbound drug in the plasma, which could increase the pharmacological or toxicological effects of the drugs.
These drug interactions can either be synergistic or antagonistic. Synergistic drug interactions are beneficial, enhancing the therapeutic effects, while antagonistic interactions could lead to harmful effects, such as reduced drug activity or increased potential for toxicity due to altered metabolism and elimination. Therefore, careful monitoring and dose adjustment may be necessary when combining highly protein-bound drugs to avoid adverse effects.