PHARMACOLOGY: Anti-Emetics

     EMS systems are evolving from entities that only exist to initiate emergency treatment of obviously life-threatening traumatic and nontraumatic conditions to those which can perform triage, identify risk factors for and sentinel signs and symptoms of potentially serious medical conditions, apply point-of-care and diagnostic testing and begin the first stages of emergency department treatment. As EMS systems mature, so does the realization that the EMS contact interval represents the first opportunity for these healthcare providers to positively affect the outcome of a subset of the ED patient population that calls 9-1-1 because they not only perceive that they have an emergency condition, but that an intervention can be made quickly to treat it.

     Such treatment for symptoms like nausea and vomiting would not have been considered the role of a paramedic even 15 years ago. These 9-1-1 patient contacts frequently began and ended with an apology for being unable to offer any treatment for the patient retching in the back of the ambulance. Today it is not only possible, but quite simple to provide prompt symptomatic relief to patients who have nausea and/or vomiting prior to their arrival in an ED.

     It is essential to recognize that not all vomiting is viral-related; there are often potentially serious medical conditions that generate these symptoms, especially in the geriatric population and those with a history of or predisposition to cardiovascular or endocrine disease. While a complete discussion of the origins of nausea and vomiting is beyond the scope and intention of this article, EMS providers who treat this patient subset must be as equally quick to ask themselves why this is happening as they are to administer an intravenous or intramuscular injection.

PREHOSPITAL ANTI-EMETICS
     There are four pharmaceuticals commonly used in EDs across the United States to treat nausea and vomiting. Three of the four are commonly available in EMS systems, although promethazine has been losing favor (see below). We have not included droperidol because its use rapidly declined after an FDA black box warning over five years ago. We have also chosen not to include pediatric dosages or pediatric-specific drug information, since children under 14 do not typically require medication with these agents in the acute care setting. Most EMS protocols also restrict delivery of anti-emetics to the adult population.

     As always, paramedics must use the medication provided by their agency and through their protocol set. In almost all scenarios, only the parenteral form of the medication will be available for prehospital use; however, you may encounter these drugs in patient's homes, since several of these agents are also available in oral or suppository form, which patients may be taking by prescription. We have listed the most common brand name next to each pharmaceutical agent for recognition purposes, although generic equivalents are available for all.

Promethazine (Phenergan)
     Promethazine is one of the phenothiazines, which were originally designed as anti-psychotics. It is primarily used as an anti-emetic, although it also contains antihistamine and sedative properties. Its mechanism of action is antagonism of central and peripheral H1 receptors.

     Promethazine is available in 12.5, 25 and 50 mg tablet form, 6.25 mg/5 ml syrup and 25 mg suppositories. Solution for injection is manufactured in concentrations of 25 mg/ml and 50 mg/ml, each in 1 ml vials. The standard adult dose is 12.5–25 mg IV, IM, PO or PR administered every four hours as needed. The maximum dose (at any one point in time) for nausea and vomiting is 50 mg given intravenously (IV), intramuscularly (IM), by mouth (PO) or by rectum (PR).