A case report from researchers at the University of Colorado Anschutz Medical Campus in Aurora links tirzepatide, sold as Zepbound, to lithium toxicity in a 50-year-old woman with bipolar disorder. It is the fourth reported case of tirzepatide-associated lithium toxicity, MedPage Today reported Oct. 26.
Jay Davis, MD, and colleagues published the case in the Journal of Clinical Psychopharmacology. The patient’s serum lithium level was 0.7 mmol/L before she started weekly 2.5-milligram tirzepatide injections for weight management.
Three weeks later, she arrived at a psychiatry appointment with a tremor in both hands, slurred speech and blurred vision. Her lithium level had climbed to 1.2 mmol/L. She had not changed her lithium dose or started other drugs, but said she was eating smaller meals and feeling full sooner.
Her physicians cut her nightly lithium dose from 900 milligrams to 450 milligrams, and her symptoms resolved. Her lithium level measured 0.4 mmol/L 17 days later. She and her physician decided not to restart tirzepatide.
Dr. Davis told MedPage that the leading explanation is that eating and drinking less causes the kidneys to reabsorb more lithium. He said incretin drugs will likely be prescribed more often to patients on lithium, and awareness of the interaction still needs to grow.
Jorge Almeida, MD, PhD, director of the bipolar disorder center at the University of Texas at Austin, was not involved in the report. He recommended checking lithium levels and kidney function within the first few weeks of starting the drug and after any dose change.
“The practical message is early monitoring, not avoidance,” Dr. Almeida told MedPage Today. “If a patient on lithium is starting one, I’d check a lithium level and kidney function within the first few weeks, and again after any dose changes.”
The report’s researchers said incretin drugs could benefit people with bipolar disorder because they work well against Type 2 diabetes and obesity, which raises the stakes for understanding the interaction.
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