Fetal Risk Summary
Metyrosine, an enzyme inhibitor, is used in patients with pheochromocytoma for preoperative preparation, management when surgery is contraindicated, or as chronic treatment of malignant pheochromocytoma. The drug inhibits tyrosine hydroxylase, the enzyme that catalyzes the conversion of tyrosine to dihydroxyphenylalanine, the first transformation in catecholamine biosynthesis (1).
No reproduction studies in animals have been located. The molecular weight of the compound (195) is low enough that transfer to the fetus should be expected.
A case report published in 1986 described the pregnancy of a 24-year-old woman at 30 weeks’ gestation who was managed for recurrent pheochromocytoma with a combination of metyrosine, prazosin (an a1-adrenergic blocker), and timolol (a b-adrenergic blocker) (2). Hypertension had been noted at her first prenatal visit at 12 weeks’ gestation. Because of declines in fetal breathing, body movements, and amniotic fluid volume that began 2 weeks after the start of therapy, a cesarean section was conducted at 33 weeks. The 1450-g female infant had Apgar scores of 3 and 5 at 1 and 5 minutes, respectively. Mild metabolic acidosis was found on analysis of umbilical cord blood gases. Multiple infarcts were noted in the placenta but no evidence of metastatic tumor. The growth-retarded infant did well and was discharged home on day 53 of life (2).
Breast Feeding Summary
No reports describing the use of metyrosine during human lactation have been located. The molecular weight (195) is low enough that excretion into breast milk probably occurs. The effects of this exposure on a nursing infant are unknown.
- Product information. Demser. Merck, 2001.
- Devoe LD, O’Dell BE, Castillo RA, Hadi HA, Searle N. Metastatic pheochromocytoma in pregnancy and fetal biophysical assessment after maternal administration of alpha-adrenergic, beta-adrenergic, and dopamine antagonists. Obstet Gynecol 1986;68:15S8S.