A patient who was in a motor vehicle accident sustained a severe head injury and is brought to the emergency department. The provider orders intravenous mannitol (Osmitrol). The nurse knows that this is given to:

Choice A reason: Synthesis of more receptor sites (upregulation) typically occurs with receptor antagonists, not agonists, as the body compensates for blocked receptors. This would increase drug sensitivity, not decrease effectiveness. For most medications, continuous exposure leads to desensitization, not receptor proliferation, making this choice incorrect for explaining tolerance.

Choice B reason: Decreased receptor selectivity implies a drug binding to unintended receptors, causing varied effects, not reduced efficacy. Tolerance results from receptor desensitization, not altered selectivity. This mechanism doesn’t explain the patient’s “immunity” to the drug’s therapeutic effects, making this choice scientifically inaccurate for the scenario.

Choice C reason: Desensitization occurs when continuous drug exposure reduces receptor responsiveness, leading to tolerance. For example, opioid receptors downregulate or internalize with prolonged agonist exposure, decreasing drug efficacy. This explains the patient’s perception of “immunity” as the drug’s effect diminishes over time, making this the correct choice.

Choice D reason: The body does not produce antagonists to compete with drugs for receptor sites. Tolerance arises from receptor desensitization or metabolic changes (e.g., enzyme induction), not endogenous antagonist production. This mechanism is not a recognized pharmacological process for reduced drug effectiveness, making this choice incorrect.

Choice A reason: Adrenergic neuron blockers, like guanethidine, reduce blood pressure by inhibiting norepinephrine release. They are not first-line for stage 1 hypertension (140-159/90-99 mm Hg). Their side effects, like orthostatic hypotension, make them less suitable. Lifestyle changes are preferred initially for this patient’s mild elevation and normal diagnostic tests, making this choice inappropriate.

Choice B reason: Beta blockers, like atenolol, reduce heart rate and cardiac output, lowering blood pressure. They are not first-line for stage 1 hypertension without compelling indications (e.g., heart failure). Guidelines recommend lifestyle modifications first for this patient’s blood pressure range, as they effectively reduce risk without medication side effects, making this choice less suitable.

Choice C reason: For stage 1 hypertension (140-159/90-99 mm Hg) with normal diagnostic tests, guidelines recommend lifestyle changes, such as diet, exercise, and weight loss, as first-line treatment. These reduce blood pressure by improving vascular health and reducing cardiac strain, offering a low-risk approach to manage mild hypertension effectively, making this the correct choice.

Choice D reason: ACE inhibitors, like lisinopril, block angiotensin II formation, reducing blood pressure. They are effective but not first-line for stage 1 hypertension without comorbidities. Lifestyle changes are prioritized to avoid medication side effects like cough or hyperkalemia, making this choice less appropriate for initial management in this patient.