Eletriptan (Relpaxa™) Causing False Positive Elevations In Urinary Metanephrines

Abstract

ABSTRACT: Objective: Pheochromocytoma is diagnosed biochemically by demonstrating an excessive production of catecholamines and their metabolites in the blood and urine. However, these tests are at times fraught with false-positive results due to drug effects. We report here a patient with markedly elevated urinary metanephrines associated with the use of eletriptan for migraine treatment. Methods: A literature search was conducted using the PubMed and Google Scholar databases for eletriptan and false positive metanephrine elevation. Urine and plasma metanephrine tests were performed via liquid chromatography/tandem mass-spectrometry. Results: A 29-year-old man with migraine recently started on eletriptan was evaluated for a worsening headache. Initially his blood pressure was 220/160 mm Hg with a creatinine of 1.9 mg/dL. He was treated with intravenous nicardipine. His lab tests showed normal aldosterone/plasma renin activity ratio, midnight salivary cortisol, thyroid function, and urinary drug screen. A 24-hour urine metanephrine level at 2,494 μg (normal, 45 to 290 μg) and normetanephrine level at 1,341 μg (normal, 82 to 500 μg) for secondary hypertension work-up were markedly elevated. In contrast, plasma metanephrines were at 27 pg/mL (normal, 0 to 62 pg/mL) and normetanephrines were at 255 pg/mL (normal, 0 to 145 pg/mL) were only mildly elevated. Adrenal CT and gallium-68 positron emission tomography/computed tomography showed no abnormalities. Within 1 week of eletriptan discontinuation, his urine and plasma metanephrine and normetanephrine levels completely normalized as well as a reduction of blood pressure (130’s/80’s mm Hg). Conclusion: The discrepancy between plasma and urine studies in our patient suggests the possibility of false positive tests. It is possible that eletriptan may affect the urine assays, but the exact mechanism causing elevated urine metanephrines/normetanephrines is not clear. Abbreviations: CYP3A4 cytochrome P450 3A4 5-HT 5-hydroxytryptamine