A nurse is caring for a client who has a new prescription for methimazole for hyperthyroidism. Which of the following findings should the nurse report to the provider as a potentially life-threatening adverse effect?

A. Sore throat: A sore throat in a client taking methimazole may indicate agranulocytosis, a potentially life-threatening adverse effect characterized by a dangerously low white blood cell count. This condition increases susceptibility to infection and requires immediate medical evaluation and discontinuation of the drug. B. Insomnia: Insomnia is not a life-threatening effect of methimazole. It may occur due to thyroid imbalance or other factors but does not indicate severe drug toxicity or bone marrow suppression. C. WBC count 12,000/mm³ (5,000 to 10,000/mm³): A mildly elevated WBC count suggests a possible infection or stress response but is not a critical concern. The danger lies in a decreased WBC count associated with agranulocytosis, not an elevation. D. Weight loss of 1 kg (2.2 pounds) in 2 weeks: Minor weight changes are expected as thyroid levels normalize during treatment. This finding does not indicate a serious or life-threatening adverse effect.