In this context it is probably most safely given by infusion since bolus doses have a propensity towards causing precipitous falls in blood pressure.
When given by injection it causes blood vessels to expand, thereby increasing blood flow. When injected into the penis (intracavernosal), it increases blood flow to the penis, which results in an erection.
It may be stored in crash carts to counteract severe peripheral vasoconstriction secondary to extravasation of peripherally placed vasopressor infusions, typically of norepinephrine. Epinephrine infusions are less vasoconstrictive than norepinephrine as they primarily stimulate beta receptor more than alpha receptors, but the effect remains dose dependent.
Phentolamine has recently been introduced in the dental field as a local anesthetic reversal agent. Distributed by Septodont, OraVerse is a Phentolamine Mesylate injection designed to reverse the local vasoconstrictor properties used in many local anesthetics to prolong anesthesia. OraVerse has been shown to accelerate the reversal of the lingering soft-tissue numbness associated with the widely used anesthetic-vasoconstrictor combinations.
^Jewell, John R.; Longworth, David L.; Stoller, James K.; Casey, David (2003). The Cleveland Clinic internal medicine case reviews. Hagerstown, MD: Lippincott Williams & Wilkins. p. 32. ISBN0-7817-4266-8.