amitriptyline and metanephrine

  • related: Pharmacology
  • amitriptyline, venlafaxine, duloxetine, nortriptyline can cause falsely elevated normetanephrine levels
  • can also occur with levodopa (substrate for catecholamine synethesis)
  • can also occur with buspirone, prochlorperazine, amphetamines
  • OTC decongestant
  • can also be elevated in Amitriptyline can cause falsely elevated normetanephrine levels and should be discontinued prior to screening for pheochromocytoma. Most pheochromocytomas secrete norepinephrine, resulting in episodic or sustained hypertension. Orthostatic hypotension can also be seen and likely reflects low plasma volume. In addition to the classic triad of diaphoresis, headache, and tachycardia, common symptoms include palpitations, tremor, pallor, and anxiety. Screening for pheochromocytoma is appropriate in this patient, following discontinuation of amitriptyline. Amitriptyline acts by inhibiting norepinephrine uptake into nerve terminals, with subsequent elevation of its metabolite, normetanephrine. False-positive elevation of plasma free normetanephrine levels can occur with other tricyclic medications such as nortriptyline or combination serotonin/norepinephrine uptake inhibitors such as venlafaxine or duloxetine. False-positive elevation of plasma normetanephrine and metanephrine levels can also occur with other medications including levodopa (a substrate for catecholamine synthesis); psychoactive medications such as buspirone, prochlorperazine, amphetamines; and over-the-counter decongestant medications that contain adrenergic receptor agonists. Plasma free metanephrines can also be elevated during acute or stressful medical situations including psychiatric illness. Therefore, unless there is significant suspicion for pheochromocytoma, testing should be delayed until the acute illness has passed. Medications that can interfere with catecholamine metabolism should be discontinued (with tapering if indicated) at least 2 weeks prior to testing for pheochromocytoma.

Omeprazole, chlorthalidone, metoprolol, and progesterone do not impact catecholamine metabolism and, therefore, can be continued during screening for pheochromocytoma.