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Zorluk: KolayPharmacologic Interventions

A 54-year-old woman is evaluated in the clinic for newly diagnosed primary hypertension. Over her last three outpatient visits, her blood pressure has averaged 154/96 mmHg. She feels well and reports no headaches, visual changes, or chest pain. Her medical history is significant only for bipolar I disorder, which has been successfully maintained for the past decade with daily lithium carbonate therapy. Her most recent laboratory studies show a normal serum creatinine level and a serum lithium concentration within the narrow therapeutic range. The physician plans to initiate first-line antihypertensive pharmacotherapy. To prevent a clinically significant pharmacokinetic drug interaction that could precipitate coarse hand tremors, ataxia, and confusion, which of the following antihypertensive medications should be avoided in this patient?

  1. HydrochlorothiazideCevap
  2. B
    Amlodipine
  3. C
    Metoprolol
  4. D
    Doxazosin
  5. E
    Hydralazine

Cevap

Hydrochlorothiazide
The correct answer is Hydrochlorothiazide. Lithium is a mood stabilizer with a very narrow therapeutic index. It is entirely excreted by the kidneys, and its reabsorption in the proximal convoluted tubule is closely linked to sodium reabsorption. Thiazide diuretics induce mild volume depletion and hyponatremia. This triggers a compensatory mechanism in the kidneys to increase the proximal tubular reabsorption of sodium. Because the kidneys cannot easily distinguish between sodium and lithium, lithium reabsorption is also markedly increased. This pharmacokinetic interaction can rapidly elevate serum lithium to toxic levels, presenting as coarse tremors, hyperreflexia, ataxia, confusion, and even seizures. Therefore, thiazides are generally avoided in patients taking lithium.

Adım Adım Çözüm

1
Identify the patient's current medication and its risk profile.
The patient is on lithium carbonate, a medication with a narrow therapeutic index that relies heavily on renal clearance.
Any medication that alters renal function or sodium handling can rapidly cause lithium toxicity.
2
Evaluate the proposed antihypertensive classes for known pharmacokinetic interactions with lithium.
Thiazide diuretics, NSAIDs, and ACE inhibitors are known to significantly reduce lithium clearance.
Recognizing absolute and relative contraindications prevents iatrogenic harm during routine medication management.
3
Select the medication from the options that matches this high-risk interaction profile.
Hydrochlorothiazide, a thiazide diuretic, is the correct choice.
Thiazides cause volume depletion and compensatory increased proximal tubular reabsorption of sodium and lithium, leading to lithium toxicity.

Anahtar Kavram

Patients on lithium therapy should avoid thiazide diuretics, nonsteroidal anti-inflammatory drugs (NSAIDs), and ACE inhibitors, as these agents decrease renal clearance of lithium and can precipitate severe neurotoxicity.
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