Phentolamine has been assigned to pregnancy category C by the FDA. Animal data have revealed slightly decreased growth and slight skeletal immaturity of the fetuses after rats and mice were given doses 24 to 30 times the usual daily human doses (UDHD, on a per kg basis). At oral doses 60 times the UDHD (on a per kg basis), a slightly lower rate of implantation was found in the rat. Phentolamine did not affect embryonic or fetal development in the rabbit at oral doses 20 times the UDHD. No teratogenic or embryotoxic effects were observed in any of the animal studies. There are no reports of adverse effects on the fetus from isolated cases in which the drug has been used to treat pheochromocytoma during human pregnancy. There are no controlled in human pregnancy. Phentolamine is only recommended for use during pregnancy when benefit outweighs risk.

The relationship between with the use of phentolamine and maternal or fetal mortality in patients with pheochromocytoma is not clear because of the significant mortality associated with this tumor. Some experts recommend caution if phentolamine must be used during pregnancy because of the risk of hypotension and decreased placental perfusion pressure. Use of this drug during pregnancy should, therefore, be limited to the treatment of acute episodes of hypertension in patients with pheochromocytoma and for the immediate preoperative and intraoperative management of such a patient undergoing Cesarean section and/or removal of the pheochromocytoma.

Phentolamine is not recommended as a diagnostic agent during pregnancy because of the availability of safer methods (urinary catecholamine levels). It is also not recommended for the chronic management of pheochromocytoma during pregnancy.

Phentolamine does not appear to adversely affect uterine contractility.

Animal studies have revealed evidence of skeletal immaturity associated with phentolamine. Immaturity was manifested by an increased incidence of incomplete or unossified calcaei and phalangeal nuclei of the hind limb and of incompletely ossified sternabrae.

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There are no data on the excretion of phentolamine into human milk. The manufacturer recommends that due to the potential for serious adverse reactions in nursing infants, a decision should be made to discontinue nursing or discontinue the drug, taking into account the importance of the drug to the mother.

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