The route of administration is the pathway by which a drug enters the body, and it directly influences how quickly and completely the medication works. In EMS, the most common routes include oral (PO), in which the drug is swallowed; sublingual, where it is placed under the tongue for absorption through the mucosal lining; intramuscular (IM) injection into muscle; inhalation or nebulization into the lungs; and rectal (PR) administration. Each route has trade-offs between speed of absorption, reliability, and patient cooperation.
Two timing concepts govern how drugs behave once given. Onset of action is the interval between administration and the start of the drug's effect, while duration of action is the total length of time the drug remains effective. A medication with a rapid onset but short duration, such as inhaled albuterol, may need to be repeated, whereas a drug with a longer duration may require fewer doses. The EMT must also understand a drug's mechanism of action, that is, how it produces its effect at the cellular or molecular level, because this underlies both the expected therapeutic response and potential adverse reactions.
Two delivery devices are particularly important in prehospital care. An auto-injector is a spring-loaded syringe that delivers a premeasured dose, often through clothing, making it ideal for emergency use by laypeople or rescuers. A metered-dose inhaler (MDI) is a handheld canister that releases a measured aerosolized dose into the lungs, often paired with a spacer to improve delivery for patients who struggle with coordination. Understanding both the route and the delivery device helps the EMT coach the patient effectively and recognize when technique is undermining the medication's effect.