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Neo-Synephrine Injection (Phenylephrine Hydrochloride Injection) - Warnings and Precautions


Boxed Warning




If used in conjunction with oxytocic drugs, the pressor effect of sympathomimetic pressor amines is potentiated (see Drug Interactions). The obstetrician should be warned that some oxytocic drugs may cause severe persistent hypertension and that even a rupture of a cerebral blood vessel may occur during the postpartum period.

Contains sodium metabisulfite, a sulfite that may cause allergic-type reactions including anaphylactic symptoms and life threatening or less severe asthmatic episodes in certain susceptible people. The overall prevalence of sulfite sensitivity in the general population is unknown and probably low. Sulfite sensitivity is seen more frequently in asthmatic than in nonasthmatic people.


NEO-SYNEPHRINE hydrochloride should be employed only with extreme caution in elderly patients or in patients with hyperthyroidism, bradycardia, partial heart block, myocardial disease or severe arteriosclerosis.

Drug Interactions
Vasopressors, particularly metaraminol, may cause serious cardiac arrhythmias during halothane anesthesia and therefore should be used only with great caution or not at all.

MAO Inhibitors
The pressor effect of sympathomimetic pressor amines is markedly potentiated in patients receiving monoamine oxidase inhibitors (MAOI). Therefore, when initiating pressor therapy in these patients, the initial dose should be small and used with due caution. The pressor response of adrenergic agents may also be potentiated by tricyclic antidepressants.

Carcinogenesis, Mutagenesis, Impairment of Fertility
No long-term animal studies have been done to evaluate the potential of phenylephrine in these areas.

Teratogenic Effects:
Pregnancy Category C.
Animal reproduction studies have not been conducted with phenylephrine. It is also not known whether phenylephrine can cause fetal harm when administered to a pregnant woman or can affect reproduction capacity. Phenylephrine should be given to a pregnant woman only if clearly needed.

Labor and Delivery
If vasopressor drugs are either used to correct hypotension or added to the local anesthetic solution, the obstetrician should be cautioned that some oxytocic drugs may cause severe persistent hypertension and that even a rupture of a cerebral blood vessel may occur during the postpartum period (see WARNINGS).

Nursing Mother
It is not known whether this drug is excreted in human milk. Because many drugs are excreted in human milk, caution should be exercised when NEO-SYNEPHRINE hydrochloride is administered to a nursing woman.

Pediatric Use
To combat hypotension during spinal anesthesia in children, a dose of 0.5 mg to 1 mg per 25 pounds of body weight, administered subcutaneously or intramuscularly, is recommended.

Page last updated: 2010-08-31

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