Lithium Poisoning

Basics

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

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