Which factor could lead to drug toxicity even at a normally prescribed dose?

The correct answer highlights that all the listed factors—decreased renal clearance due to kidney disease, changes in serum protein binding caused by disease, and the impact of discontinuing or administering another drug—can contribute to drug toxicity at normally prescribed doses.

Decreased renal clearance, especially in patients with kidney disease, can lead to the accumulation of drugs in the body. Normally, the kidneys filter and excrete drugs, but when their function is compromised, this process slows down, resulting in higher drug levels and potential toxicity.

Altered serum protein binding is another crucial factor. Many drugs bind to plasma proteins, and various diseases can change the levels or functionality of these proteins. If a drug binds less effectively or if there is a decrease in protein levels, more of the free (active) drug remains in circulation, leading to increased effects or toxicity.

Discontinuing or adding other medications can also significantly affect a patient’s response to a drug. This can occur due to drug-drug interactions where one drug can increase the levels of another by affecting its metabolism or excretion.

Since each of these factors can independently lead to an increased risk of drug toxicity, the option that includes all of them accurately encapsulates the complexities of pharmacotherapy and the potential risks associated with