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Zorluk: ZorPsychopharmacology and Psychological Therapies

A 62-year-old retired architect with a long-standing history of bipolar I disorder is evaluated in the emergency department for worsening confusion, sluggishness, and an unsteady gait over the past three days. He has been psychiatrically stable on a fixed dose of lithium carbonate for eight years without any recent dosage adjustments. His husband reports that the patient recently started taking an over-the-counter analgesic multiple times a day for a severe flare-up of knee osteoarthritis. Vital signs are within normal limits. Physical examination reveals a coarse, irregular tremor in both upper extremities and pronounced dysarthria. The patient is unable to perform tandem walking without losing his balance. Which of the following mechanisms best explains how the newly initiated analgesic precipitated this patient's current symptoms?

  1. Decreased renal clearance secondary to afferent arteriole vasoconstrictionCevap
  2. B
    Enhanced proximal tubular reabsorption secondary to intravascular volume depletion
  3. C
    Inhibition of hepatic cytochrome P450 enzymes leading to impaired drug metabolism
  4. D
    Displacement of the psychotropic medication from plasma transport proteins
  5. E
    Synergistic overactivation of central postsynaptic serotonergic receptors

Cevap

The over-the-counter medication (an NSAID) precipitated toxicity via decreased renal clearance secondary to afferent arteriole vasoconstriction.
The correct answer accurately describes the mechanism of NSAID-induced lithium toxicity. This patient is presenting with classic symptoms of lithium toxicity (coarse tremor, ataxia, dysarthria, and altered mental status). His recent initiation of an over-the-counter analgesic for osteoarthritis points strongly to a nonsteroidal anti-inflammatory drug (NSAID). NSAIDs inhibit cyclooxygenase (COX), leading to decreased synthesis of prostaglandins. In the kidney, prostaglandins are responsible for maintaining vasodilation of the afferent arteriole. Loss of this dilatory effect results in afferent arteriole vasoconstriction, a decreased glomerular filtration rate (GFR), and subsequently decreased renal clearance of lithium. Because lithium has a very narrow therapeutic index, this reduction in clearance rapidly leads to toxic serum levels.

Adım Adım Çözüm

1
Diagnose the patient's acute clinical presentation based on symptoms and medication history.
The patient is experiencing acute lithium toxicity, characterized by confusion, coarse tremors, ataxia, and dysarthria in the setting of chronic lithium use.
Lithium has a narrow therapeutic index, and its neurological toxicities classically include coarse tremor, cerebellar dysfunction (ataxia, dysarthria), and altered mental status.
2
Identify the likely over-the-counter medication taken for the patient's osteoarthritis.
The patient is most likely taking a nonsteroidal anti-inflammatory drug (NSAID) such as ibuprofen or naproxen.
NSAIDs are standard, widely available over-the-counter first-line analgesics for osteoarthritis flare-ups.
3
Determine the pharmacological mechanism by which NSAIDs interact with lithium.
NSAIDs inhibit cyclooxygenase (COX), reducing renal prostaglandins. This causes afferent arteriole vasoconstriction, dropping the glomerular filtration rate (GFR) and decreasing the renal clearance of lithium.
Lithium is filtered exclusively by the kidneys. Any drug that reduces GFR (NSAIDs) or increases proximal tubular reabsorption (thiazides, ACE inhibitors) will lead to toxic accumulation of lithium.

Anahtar Kavram

Lithium relies entirely on renal clearance. Medications that decrease glomerular filtration rate, such as NSAIDs (via afferent arteriole vasoconstriction), can precipitate dangerous lithium toxicity.
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Psychopharmacology and Psychological Therapies

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