A 26-year-old woman with bipolar disorder has been stable on lithium for 2 years. She presents to the PMHNP with mild confusion, a tremor, and nausea. Upon questioning, she states she recently fell while running and injured her ankle in the fall. Which of the following is most likely to be the cause of her current symptoms?

Choice A reason: Acetaminophen is generally safe to use with lithium and does not interfere with renal function or lithium clearance. It is unlikely to cause lithium toxicity or contribute to the symptoms described. Choice B reason: Vicodin contains hydrocodone and acetaminophen. While opioids can cause sedation and nausea, they do not typically interact with lithium in a way that would cause toxicity. However, they should still be used cautiously in patients with mood disorders. Choice C reason: Aspirin is an NSAID but has a lesser impact on renal prostaglandins compared to other NSAIDs. It is less likely to impair lithium clearance and cause toxicity, although caution is still advised. Choice D reason: Ibuprofen is a nonsteroidal anti-inflammatory drug (NSAID) that can reduce renal clearance of lithium by inhibiting prostaglandin synthesis in the kidneys. This can lead to elevated lithium levels and toxicity, especially in older adults or those with compromised renal function. The client’s symptoms—confusion, tremor, and nausea—are consistent with lithium toxicity, making ibuprofen the most likely culprit.