A nurse is reviewing the medical record of a client who has been taking lithium. Which of the following findings should the nurse notify the provider of immediately?

Lithium is a mood stabilizer commonly used in the management of bipolar disorder, particularly for the treatment and prevention of manic episodes. It has a narrow therapeutic index, meaning that the difference between therapeutic and toxic levels is small. Lithium is excreted primarily through the kidneys, and factors that affect renal function, sodium balance, or fluid status can significantly increase the risk of toxicity. Neurological manifestations are among the earliest and most serious indicators of lithium toxicity and require immediate intervention. Rationale: A. Drowsiness is an early and relatively mild manifestation of lithium accumulation and may occur when serum levels begin to rise above the therapeutic range. While it should be monitored closely, it is not the most critical or immediately life-threatening finding. It can be associated with mild toxicity or dose adjustment needs, but does not independently indicate severe toxicity requiring emergency intervention. B. Seizure is a severe and life-threatening manifestation of lithium toxicity and indicates significant central nervous system involvement. As lithium levels rise, neuronal excitability becomes increasingly impaired, leading to tremors, confusion, ataxia, and eventually seizures or coma. The occurrence of seizures requires immediate discontinuation of lithium, urgent medical intervention, and possible emergency treatment such as airway support and hemodialysis. C. Weight gain is a common long-term side effect of lithium therapy due to metabolic changes and fluid retention. While it may be distressing for the client and require counseling on diet and lifestyle, it is not an acute sign of toxicity. It does not require immediate provider notification unless associated with other concerning symptoms. D. Muscle weakness can occur with lithium therapy and may be related to electrolyte imbalances or mild neuromuscular effects. However, it is not a definitive indicator of severe toxicity on its own. It should be assessed in conjunction with other symptoms such as tremors, confusion, or gastrointestinal distress to determine clinical significance.