Does Metyrosine Have Cardiac Side Effects?
Yes, metyrosine has significant cardiac side effects, most notably life-threatening arrhythmias during anesthesia and surgery, as well as risks of hypotension and decreased perfusion of vital organs, particularly after tumor removal. 1
Direct Cardiac Effects During Surgery
The FDA label explicitly warns that life-threatening arrhythmias may occur during anesthesia and surgery in patients taking metyrosine, requiring treatment with beta-blockers or lidocaine. 1 This necessitates continuous monitoring of blood pressure and electrocardiogram throughout the surgical procedure. 1
Hemodynamic Instability
- Hypotension and decreased perfusion of vital organs can result from vasodilatation and expanded volume capacity, especially after tumor removal. 1
- Large volumes of plasma may be needed postoperatively to maintain blood pressure and central venous pressure within normal range. 1
- Adequate intravascular volume must be maintained intraoperatively and postoperatively when metyrosine is used, particularly in combination with alpha-adrenergic blocking drugs. 1
Clinical Evidence of Cardiovascular Effects
Intraoperative Blood Pressure Control
Research demonstrates that metyrosine significantly reduces intraoperative peak systolic pressures (mean 168 ± 27 mm Hg with metyrosine vs 243 ± 40 mm Hg without preoperative treatment, P < 0.05). 2 However, metyrosine does not eliminate the danger of hypertensive crises or arrhythmias during tumor manipulation, and phentolamine may still be needed. 1
Variable Efficacy and Cardiac Risks
- In one case report, despite adequate blood pressure control leading up to resection, significant hypertension (up to 201/110 mmHg) developed upon tumor manipulation despite metyrosine therapy. 3
- This indicates that metyrosine may be unsatisfactory as monotherapy in achieving sufficient inhibition of catecholamine synthesis in some patients with actively secreting tumors. 3
Additional Cardiovascular Considerations
Interaction with CNS Depressants
Metyrosine may add to the sedative effects of alcohol and other CNS depressants, which could indirectly affect cardiovascular stability. 1
Monitoring Requirements
Continuous monitoring of blood pressure and electrocardiogram is mandatory during surgery for patients on metyrosine. 1 This reflects the serious nature of potential cardiac complications.
Clinical Context
While metyrosine can improve intraoperative outcomes when used appropriately (95% of patients receiving metyrosine did not require pressors intraoperatively vs 50% with phenoxybenzamine alone 2), the cardiac risks remain substantial. The drug should be reserved for high-risk situations such as difficult pheochromocytoma resections, large anticipated catecholamine releases, or when standard alpha- and beta-adrenergic blockade cannot adequately control hypertension. 4