A nurse is preparing to administer amlodipine to a client. Which of the following vital signs should the nurse assess before administration?

Amlodipine is a long-acting dihydropyridine calcium channel blocker that inhibits the transmembrane influx of calcium ions into vascular smooth muscle. It primarily causes systemic vasodilation, effectively reducing peripheral vascular resistance and lowering arterial blood pressure in hypertensive patients. Rationale: A. Oxygen saturation is a measure of hemoglobin oxygen binding and is not directly affected by the administration of calcium channel blockers like amlodipine. While respiratory assessment is part of general nursing care, it is not the priority parameter for a medication that targets vascular resistance. Amlodipine does not interfere with pulmonary gas exchange or the oxygen-carrying capacity of the blood. B. Heart rate is a critical assessment for non-dihydropyridines like diltiazem, but amlodipine has minimal effect on the sinoatrial or atrioventricular nodes. Because amlodipine is vascular-selective, it does not typically cause the bradycardia associated with other calcium channel blockers. While reflexive tachycardia can occur due to vasodilation, blood pressure remains the most vital parameter to assess prior to dosing this specific agent. C. Blood pressure must be assessed before administering amlodipine because its primary pharmacological effect is to lower systemic blood pressure through vasodilation. Giving the medication to a patient who is already hypotensive could lead to severe cardiovascular compromise, dizziness, or syncope. The nurse must ensure the client's pressure is within the safe parameters established by the provider to prevent iatrogenic hypotension. D. Respiratory rate is not influenced by amlodipine, as the drug does not act on the central nervous system respiratory centers or the musculature of the diaphragm. Unlike opioids or certain sedatives, amlodipine does not carry a risk of respiratory depression. Monitoring the breathing rate, while standard, does not provide information relevant to the safety or hemodynamic impact of this antihypertensive medication.