**Core Concept**
Isolated systolic hypertension (ISH) is a condition characterized by elevated systolic blood pressure (≥140 mmHg) with normal diastolic blood pressure (<90 mmHg) in the absence of other cardiovascular risk factors. The primary goal of treatment is to reduce the systolic blood pressure to <140 mmHg to prevent cardiovascular complications. **Why the Correct Answer is Right** The most appropriate medication for this patient is a dihydropyridine calcium channel blocker (CCB), such as amlodipine. CCBs are first-line agents for ISH due to their ability to reduce peripheral resistance and lower systolic blood pressure. They are also effective in reducing cardiovascular events and have a favorable safety profile. The mechanism of action involves inhibiting L-type calcium channels in vascular smooth muscle cells, leading to vasodilation and decreased peripheral resistance. **Why Each Wrong Option is Incorrect** **Option A:** Thiazide diuretics, such as hydrochlorothiazide, are not the preferred initial treatment for ISH, as they may worsen postural hypotension and electrolyte imbalances in older adults. **Option B:** Beta-blockers, like metoprolol, are not typically used as first-line agents for ISH, as they may not provide sufficient reduction in systolic blood pressure and may have adverse effects on cardiac output in older adults. **Option C:** Angiotensin-converting enzyme (ACE) inhibitors, such as lisinopril, are not the first choice for ISH, as they may not provide sufficient reduction in systolic blood pressure and may have adverse effects on renal function in older adults. **Clinical Pearl / High-Yield Fact** When initiating antihypertensive therapy in older adults with ISH, it's essential to start with a low dose and titrate gradually to avoid postural hypotension and electrolyte imbalances. **Correct Answer: A. Amlodipine.**