SAT-192 Eletriptan (RelpaxaTm) Causing False Positive Elevations in Urinary Metanephrine

Abstract

Background:The diagnosis of pheochromocytoma depends crucially on the demonstration of excessive production of catecholamines. This step, however, is fraught with several difficulties, in particular with false-positive test results. Drugs such as phenoxybenzamine and tricyclic antidepressants are the most frequently associated causes for false-positive results. Other medications are also known to cause a false positive elevation of urinary metanephrines. We are reporting a patient with markedly elevated urine metanephrines associated with the use of Eletriptan hydrobromide (RelpaxaTM), a drug commonly used for treating migraine.Clinical Case:A 29-year-old man with a history of migraine managed on ibuprofen and recently started Eletriptan presented to the emergency room complaining of a 24-hour history of progressively worsening headaches. At the time of initial evaluation his blood pressure was in the 220s/160s with a creatinine of 1.9 mg/dL with unknown baseline. He was managed on an IV nicardipine drip. Due to his young age he underwent an evaluation for secondary causes of his hypertension. Laboratory: normal aldosterone/renin level (ratio was 0.4), normal midnight salivary cortisol and normal thyroid function studies. Urine screening for drug abuse was also negative. A 24-hour urine metanephrine level, while the patient was taking Eletriptan, was markedly elevated (normetanephrine 1341mcg (ref 82–500) and metanephrine level of 2494 mcg (ref 45–290). In contrast, the plasma metanephrines were only mildly elevated (metanephrines level 27 pg/ml (ref 0–62) and normetanephrine level of 255 pg/ml (ref 0–145)). Adrenal CT did not reveal any evidence of adrenal nodules. Additionally a Gallium-68 PET/CT scan did not reveal any evidence of pheochromocytoma or paraganglioma. Eletriptan was discontinued and his blood pressure was controlled on oral medications. Within one week of stopping Eletriptan his urine metanephrines (metanephrine 76 mcg/ 24 hrs, normetanephrine 277 mcg/dL) and plasma metanephrines (metanephrine 39 pg/mL, normetanephrine 148 pg/mL) normalized. Conclusion: The discrepancy between plasma and urine metanephrines in our patient suggests the possibility of a false positive test. Eletriptan, a second generation triptan drug, is a selective 5-hydroxytryptamine 1B/1D receptor agonist and has been shown to reduce carotid arterial blood flow, with only a small increase in arterial blood pressure at high doses. However, Eletriptan has no significant affinity or pharmacological activity at adrenergic α1, α2, or β; dopaminergic D1 or D2; muscarinic; or opioid receptors. It is also interesting to note that Eletriptan use is contraindicated in uncontrolled hypertension. It is possible Eletriptan may affect the assay of urine metanephrines. However, the exact mechanism of Eletriptan causing elevated urine metanephrines in our patient is not clear.