A client experiences residual effects following an acute attack of Ménière's disease and receives a new prescription for an antihistamine. Which assessment finding indicates that the medication is effective?

A. Ambulates easily without vertigo: Ménière’s disease primarily affects the inner ear, causing episodes of vertigo, dizziness, and imbalance. Antihistamines are used to reduce vestibular stimulation and alleviate vertigo. If the client can ambulate without experiencing dizziness or loss of balance, this demonstrates that the antihistamine is effectively controlling vestibular symptoms, which is the intended therapeutic outcome. B. Headache pain rated 0 on a 0 to 10 scale: While relief of headache may indicate general comfort, antihistamines are not primarily prescribed to treat pain in Ménière’s disease. Headache assessment does not provide specific evidence of improved vestibular function or effectiveness of the antihistamine in controlling vertigo. C. Blood pressure of 120/80 mm Hg: A normal blood pressure reading indicates cardiovascular stability but is not directly related to the efficacy of an antihistamine for Ménière’s disease. Blood pressure monitoring is routine but does not reflect the medication’s impact on vertigo or balance. D. Oxygen saturation level of 99% on room air: Adequate oxygen saturation shows sufficient oxygenation but does not correlate with the control of inner ear-related vertigo. This finding is unrelated to the therapeutic goal of the antihistamine for managing residual effects of Ménière’s disease.