Lithium Poisoning

Basics

Description

  • GI absorption is rapid:
    • Regular release: Peak serum levels 2–4 hr
    • Sustained release: Peak serum levels 4–12 hr
  • Half-life 24 hr
  • Slow distribution (at least 6 hr)
  • Volume of distribution 0.6–0.9 L/kg
  • Elimination:
    • Not metabolized
    • Renal excretion (unchanged)
    • Reabsorbed in the proximal tubules by sodium transport mechanism
    • Elimination half-life (therapeutic) is 20–24 hr and prolonged in chronic users
  • Therapeutic and toxic indices:
    • Therapeutic and toxic effects occur only when lithium is intracellular
    • Narrow toxic-to-therapeutic ratio
    • Therapeutic level 0.6–1.2 mEq/L (postdistribution)
    • Because of small size, renal handling is similar to sodium, potassium, and magnesium
  • Risk factors:
    • Acute conditions increasing risk of toxicity:
      • Dehydration (larger percent reabsorbed)
      • Overdose
    • Chronic conditions:
      • Hypertension
      • Diabetes mellitus
      • Renal failure
      • Congestive heart failure
      • Advanced age
      • Dose change
      • Drug interactions
      • Lithium therapy
      • Low-salt diet
    • The following may result in increased serum lithium levels due to decreased renal clearance or exacerbated effects:
      • NSAIDs
      • Thiazide diuretics
      • ACE inhibitors
      • Phenytoin
      • Tricyclic antidepressants
      • Phenothiazines

Etiology

  • Acute or chronic conditions affecting lithium clearance
  • Overdose

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