Which of the following can increase lithium levels in the body?

Angiotensin-converting enzyme (ACE) inhibitors can indeed increase lithium levels in the body due to their impact on renal function and fluid balance. Lithium is primarily excreted by the kidneys, and any factor that affects renal blood flow or glomerular filtration can influence lithium clearance. ACE inhibitors are known to cause changes in kidney function, particularly affecting the renal blood supply and potentially reducing the glomerular filtration rate (GFR). This reduction in GFR can lead to higher serum levels of lithium as the kidneys may not be able to excrete it as effectively.

The use of ACE inhibitors, especially in conjunction with lithium therapy, necessitates the careful monitoring of lithium levels to avoid toxicity. Regular blood tests are important to ensure that lithium levels remain within the therapeutic range, as increased levels can lead to serious side effects, including neurological and gastrointestinal toxicity.

In contrast, caffeine generally has a diuretic effect and may actually reduce lithium levels. Fluoxetine, as an SSRI, is not known to have a direct effect on lithium levels but can potentially influence mood stabilization in those already on lithium therapy. Calcium supplements do not have a significant interaction with lithium metabolism or excretion. Understanding these dynamics is crucial for managing patients on lithium therapy effectively.