Medroxyprogesterone (Depo Provera) is prescribed IM to create a storage reservoir of the drug. Storage reservoirs:

Correct Answer: C

Rationale: The correct answer is C because storage reservoirs increase the length of time a drug is available and active in the body. By administering medroxyprogesterone IM, a storage reservoir is created in the muscle tissue, allowing for a slow and sustained release of the drug over time. This helps maintain therapeutic levels of the medication in the bloodstream, prolonging its effects. Incorrect answers: A: Assuring the drug reaches its intended target tissue is related to factors such as drug transport mechanisms, not storage reservoirs. B: Loading doses are given to achieve therapeutic levels quickly, not necessarily due to storage reservoirs. D: Storage reservoirs are not limited to collagen tissues; they can be present in various tissues depending on the drug's properties.

Correct Answer: C

Rationale: The correct answer is C: Desensitization or down-regulation with continuous use. Receptor agonists continuously activate receptors, leading to desensitization or down-regulation where the receptors become less responsive or decrease in number. This occurs due to the body's attempt to maintain homeostasis in response to constant stimulation. Choices A and D are incorrect because receptor agonists do not typically bind irreversibly or exhibit an inverse relationship between drug concentration and action. Choice B is incorrect as up-regulation is usually observed in response to receptor antagonists, not agonists.

Correct Answer: B

Rationale: The correct answer is B because drugs administered via IV route enter the bloodstream directly, allowing for immediate distribution throughout the body. This rapid distribution leads to fast onset of action. Choice A is incorrect as lipid solubility is not a requirement for IV absorption. Choice C is incorrect because nonionized drugs are not necessarily easily absorbed via IV route. Choice D is incorrect as pinocytosis is not a mechanism for drug absorption via IV route.

Correct Answer: B

Rationale: The correct answer is B because the blood-brain barrier is designed to restrict the passage of many drugs into and out of brain cells, regulating the entry of substances to protect the brain from harmful agents. Explanation: 1. The blood-brain barrier is a specialized structure that tightly regulates the passage of substances from the bloodstream into the brain. 2. Many drugs, especially water-soluble and ionized ones (choice A), face difficulty crossing this barrier due to their properties. 3. The fetal-placental barrier (choice C) primarily protects the fetus from harmful substances but does not slow drug entry into brain cells. 4. Lipid-soluble drugs (choice D) can actually pass through these barriers easily due to their chemical properties, posing risks for pregnant women. In summary, choice B is correct as it accurately describes the role of the blood-brain barrier in controlling drug entry into brain cells, while the other choices present inaccurate statements regarding these distribution barriers.

Correct Answer: D

Rationale: Step-by-step rationale for why choice D is correct: 1. Unbinding a nonvolatile drug from plasma proteins increases the drug's free concentration in the blood. 2. Increased free drug concentration enhances the drug's ability to be filtered by the kidneys. 3. Higher filtration of the drug leads to increased excretion through the renal system. 4. Therefore, unbinding a nonvolatile drug from plasma proteins enhances the body's ability to excrete the drug efficiently. Summary of why other choices are incorrect: A: Reduced circulation and perfusion of the kidney would decrease the excretion of drugs. B: Chronic renal disease impairs renal function, reducing drug excretion. C: Competition for a transport site by another drug may affect distribution but not necessarily increase drug excretion.