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Difficulty: MediumPharmacologic Interventions

A 45-year-old man comes to the clinic for a routine follow-up. He has a 5-year history of bipolar I disorder, which has been well-controlled on lithium monotherapy. He has not experienced a manic or depressive episode since starting this medication. Over his last three clinic visits, his blood pressure has been consistently elevated, averaging 154/92154/92 mm Hg. He has strictly adhered to a low-sodium diet and a regular aerobic exercise program for the past 6 months without significant improvement in his blood pressure. His body mass index is 2626 kg/m 2^2. The remainder of his physical examination is unremarkable. Laboratory studies reveal a serum creatinine of 0.90.9 mg/dL and a serum lithium level of 0.80.8 mEq/L (therapeutic range: 0.6−1.20.6-1.2 mEq/L). A decision is made to initiate pharmacologic therapy for his essential hypertension. Which of the following is the most appropriate initial antihypertensive medication for this patient?

  1. A
    Lisinopril
  2. B
    Hydrochlorothiazide
  3. AmlodipineAnswer
  4. D
    Metoprolol
  5. E
    Verapamil

Answer

Amlodipine is the most appropriate initial antihypertensive medication for a patient on lithium.
The correct answer is amlodipine. It is a dihydropyridine calcium channel blocker and is considered a first-line antihypertensive agent. Importantly, it does not significantly alter lithium clearance or increase the risk of neurotoxicity, making it the safest and most appropriate choice for a patient stabilized on lithium therapy.

Step-by-Step Solution

1
Evaluate the indication for pharmacotherapy.
The patient has essential hypertension refractory to lifestyle modifications, requiring medical therapy.
Sustained blood pressure elevation above guideline thresholds warrants intervention to reduce long-term cardiovascular risk.
2
Identify the patient's existing medications and potential drug interactions.
The patient is on lithium. Thiazide diuretics, ACE inhibitors, ARBs, and non-dihydropyridine CCBs must be avoided.
Thiazides and ACE inhibitors/ARBs decrease lithium clearance, leading to toxicity. Non-dihydropyridine CCBs increase the risk of severe neurotoxicity.
3
Select the safest first-line antihypertensive agent.
Amlodipine is selected as the initial therapy.
Amlodipine is a dihydropyridine CCB, which is a first-line agent for essential hypertension and does not adversely interact with lithium.

Key Concept

In patients taking lithium, first-line antihypertensive agents such as thiazide diuretics and ACE inhibitors/ARBs must be avoided as they decrease lithium clearance and precipitate toxicity. Dihydropyridine calcium channel blockers (e.g., amlodipine) are safe and effective alternatives.
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Pharmacologic Interventions

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