Jen has Bipolar Type I disorder and is on Lithium. She is an active person who runs and bicycles frequently. Last summer Jen took a 20-mile bike ride in 90-degree weather, sweated profusely and did not take in adequate fluids. Based on your knowledge of Lithium and fluid dynamics, you would expect Jen's serum Lithium level to:

Choice A reason: While an increase above 1.0 mEq/L may indicate a higher therapeutic range, it does not necessarily indicate toxicity. Toxicity is more likely when levels exceed 1.5 mEq/L. This choice underestimates the severity of the fluid loss and its impact on lithium clearance. Choice B reason: This is incorrect. Dehydration and sodium loss from excessive sweating reduce renal clearance of lithium, leading to accumulation and increased serum levels, not a decrease. Lithium is excreted by the kidneys, and any condition that reduces renal perfusion or sodium levels can precipitate toxicity. Choice C reason: This is correct. Dehydration from prolonged exercise and heat exposure, combined with inadequate fluid intake, can lead to reduced renal clearance of lithium. This increases the risk of lithium accumulation and toxicity, especially when serum levels rise above 1.5 mEq/L. Symptoms of toxicity include tremors, confusion, ataxia, and in severe cases, seizures or coma. Choice D reason: This is incorrect. Significant fluid loss and electrolyte imbalance are expected to affect lithium levels. Assuming no change disregards the pharmacokinetics of lithium and the impact of hydration status on renal excretion.