A Review of Lithium Overdose

Lithium Toxicity. 

Lithium is rapidly and almost completely absorbed into the bloodstream. It is not metabolized in the body and is excreted by the kidneys unchanged in the urine. Therefore, any type of renal injury/insufficiency can result in lithium toxicity. If you are concerned about lithium toxicity, keep renal function in mind when considering the etiology and management.

Lithium toxicity can be divided into three categories, each with varying presentation depending on how much of the drug has crossed into the CNS. The therapeutic serum level is 0.6-1.2mEq/L, and it is important to note that the serum level only roughly correlates with clinical symptoms.

Acute toxicity:  This is typically due to acute intentional overdoses in naive patients – there is less time for drug to diffuse into CNS. GI symptoms, as lithium is an irritant, include nausea, vomiting, diarrhea and generalized abdominal pain. Cardiac abnormalities include bradycardia, hypotension and ventricular dysrhythmias.

Chronic toxicity: This may occur due to a change in lithium dosage or decreased renal clearance. The earlier effects are neurologic and include tremors, muscle fasciculation, clonus, choreoathetosis (irregular twisting contractions), ataxia, dysarthria, agitation, lethargy and seizure. These signs and symptoms can even occur at therapeutic levels.

Acute on Chronic toxicity: This may be seen in patients undergoing treatment with lithium who ingest an additional amount. They will exhibit both GI and neurologic symptoms.

Lithium serum levels should be ordered in any patient with a concerning presentation and history of lithium use.

ECG – prolonged QTc and diffuse T-wave inversions

TSH/T4 – may see lithium-induced hypothyroidism

BUN/crn – the kidneys are the only way lithium is eliminated!

CBC – basic labwork; of note lithium may cause elevated white count

Na, Ca – may cause nephrogenic diabetes insipidus and hyperparathyroidism

 

Intubate if the patient is severely altered and cannot protect airway. IV normal saline is important as patients are often polyuric and dehydrated. The goal is to maintain kidney function for lithium excretion. Whole bowel irrigation is only indicated in acute ingestion of extended release pills and only effective if given in a timely manner (as lithium is rapidly absorbed). Hemodialysis is indicated in severe toxicity or in patients with impaired renal function. There are no clear recommendations on when to dialyze based on serum concentration; always consider the clinical picture and the ability of the patient to excrete lithium. Recommendations for dialysis can range from lithium levels > 2.5 mEQ/L  to as high as  > 4.0mEQ/L.

Acute ingestion without symptoms: Monitor 4-6 hours; admit if serum >1.5mEq/L. Mild toxicity with normal renal function: IV saline for 6-12 hours in observation; discharge when serum <1.5mEq/L. Moderate toxicity with decreased renal function or severe toxicity with CNS symptoms should be managed in the ICU.

 

References:

Schneider S.,Cobaugh D. and B. Kessler. “Chapter 181. Lithium.”Tintinalli’s Emergency Medicine: A Comprehensive Study Guide, 8e. Eds. Judith E. Tintinalli, et al. New York, NY: McGraw-Hill, 2015. n. pag. AccessMedicine.Web. 8 Nov. 2016.