Lithium

Lithium, a mineral salt used in the treatment of bipolar disorder, has a narrow therapeutic index (ie, the clinically effective dose is only slightly lower than the dose at which it becomes toxic). Lithium is eliminated exclusively by the kidneys and also passes across cell membranes via transport proteins that normally handle sodium and potassium. As a result, medications that suppress the glomerular filtration rate or affect potassium and sodium levels can increase lithium levels and lead to potential drug toxicity. Thiazide diuretics, angiotensin-converting enzyme inhibitors, and angiotensin II receptor blockers can increase serum lithium levels. Calcium channel blockers (eg, amlodipine) are usually considered safe as they do not significantly affect sodium levels or glomerular filtration rate.