Comprehensive Nursing Pharmacology Q 269
When a drug is 50% protein-bound, it means that:
A. 50% of the drug destroys protein.
B. 50% of the dose is at work.
C. 50% of the drug is excreted in the kidneys.
D. Protein must be restricted in the diet.
Correct Answer: B. 50% of the dose is at work
The percentage of drugs, not protein-bound is the amount of drug that is free to exert its effect on the body’s tissues. The other options are incorrect because protein binding has nothing to do with the destruction of protein, drug excretion, or protein in the diet. Note that the concept of “50% bound” literally means that 50% is BOUND or connected to protein. This means that the remaining 50% is available.
Option A: Plasma protein binding refers to the degree to which medications attach to proteins within the blood. A drug’s efficiency may be affected by the degree to which it binds. The less bound a drug is, the more efficiently it can traverse cell membranes or diffuse.
Option C: Protein-binding may affect drug activity in one of two ways: either by changing the effective concentration of the drug at its site of action or by changing the rate at which the drug is eliminated, thus affecting the length of time for which effective concentrations are maintained.
Option D: Many drugs in circulation are bound to plasma proteins, and because the bound drug is too large to pass through biological membranes, only free drugs are available for delivery to the tissues and to produce the desired pharmacological action. Therefore the degree of protein binding can greatly affect the pharmacokinetics of drugs.