Background
Lithium has been in use since the 1870s. Lithium was initially used to treat depression, gout, and neutropenia, and for cluster headache prophylaxis, but it fell out of favor because of its side effects. In the 1940s, the US Food and Drug Administration (FDA) banned the use of lithium because of fatalities but lifted the ban in 1970. Presently, lithium is commonly used as maintenance treatment of bipolar disorder. Lithium poisoning occurs frequently, since it is used in a population at high risk for overdose. Furthermore, lithium has a relatively narrow therapeutic index that predisposes patients on chronic lithium maintenance treatment to poisoning with relatively minor changes in medications or health status.
Pathophysiology
The central nervous system (CNS) is the major organ system affected, although the renal, gastrointestinal (GI), endocrine, and cardiovascular (CV) systems also may be involved.
Lithium is available only for oral administration. It is almost completely absorbed from the GI tract. Peak levels occur 2-4 hours postingestion, although absorption can be much slower in massive overdose or with ingestion of sustained-release preparations.
Lithium dosing
Lithium is minimally protein bound (< 10%) and has an apparent volume of distribution of 0.6-1 L/kg. The therapeutic dose is 300-2700 mg/d with desired serum levels of 0.6-1.2 mEq/L.
Lithium clearance is predominantly through the kidneys. Because it is minimally protein bound, lithium is freely filtered at a rate that is dependent upon the glomerular filtration rate (GFR). Consequently, dosing must be adjusted based on renal function. Individuals with chronic renal insufficiency must be closely monitored if placed on lithium therapy.
Most filtered lithium is reabsorbed in the proximal tubule; thus, drugs known to inhibit proximal tubular reabsorption, such as carbonic anhydrase inhibitors and aminophylline, may increase excretion. Diuretics acting distally to the proximal tubule, such as thiazides and spironolactone, do not directly affect the fractional excretion of lithium (although they may affect serum lithium levels indirectly through their effects on volume status). Reabsorption of lithium is increased and toxicity is more likely in patients who are hyponatremic or volume depleted, both of which are possible consequences of diuretic therapy.
Lithium half-life
The plasma elimination half-life of a single dose of lithium is from 12-27 hours (varies with age). The half-life increases to approximately 36 hours in elderly persons (secondary to decreased GFR). Additionally, half-life may be considerably longer with chronic lithium use.
Epidemiology
Frequency
United States
An estimated 10,000 toxic exposures occur per year. These data indicate a gradual increase over the past 10 years.
Mortality/Morbidity
An estimated 2000 moderate-to-severe outcomes occur in the United States each year; lethal outcomes are generally secondary to severe CNS effects with subsequent cardiovascular collapse.
Race
No predilection exists.
Age
Approximately 10% of toxic lithium exposures occur in children younger than 19 years.
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