18.3 Medication Routes: Enteral, Parenteral, Inhaled & Topical Administration

18.3 Medication Routes: Enteral, Parenteral, Inhaled & Topical Administration

CPCF Appendix A minimum entry-to-practice skill #32 names eleven routes the Primary Care Paramedic must be able to use: buccal, endotracheal, inhalation (not including oxygen), intramuscular, intranasal, intraosseous, intravenous, oral, subcutaneous, sublingual, and topical. Foundational knowledge #5 adds the characteristics of injection sites and the preparation of patient and supplies. Which routes a given PCP may actually use depends on the provincial regulator and the medical directive — but all eleven are examinable content.

Choosing a Route

The choice is driven by three questions: how fast is the effect needed, is the drug formulated for that route, and can this patient use it safely.

Enteral Routes

Oral (PO)

Simplest and safest when appropriate, but subject to first-pass metabolism and requiring an intact swallow and protective airway reflexes.

• Contraindicated in decreased level of consciousness, absent gag, active vomiting, suspected bowel obstruction, and in any patient likely to need urgent surgery or anaesthesia.
• Oral glucose gel is a common PCP medication and requires an alert, cooperative patient able to swallow. Never place gel in the mouth of a patient who cannot protect their airway.
• Chewable ASA is chewed rather than swallowed to accelerate absorption across the buccal and upper gastrointestinal mucosa.

Sublingual (SL) and Buccal

Placed under the tongue (sublingual) or between the cheek and gum (buccal). Both mucosae are thin, highly vascular, and drain into veins returning directly to the systemic circulation, bypassing first-pass hepatic metabolism — the reason sublingual nitroglycerin works when swallowed nitroglycerin does not.

• Requires a moist mucosa: a dry mouth substantially slows absorption. Moisten with a little water if needed.
• The patient must not swallow the tablet or spray, and must not eat or drink until it has dissolved.
• Do not use in an unconscious patient or one who cannot follow the instruction.
• Sublingual nitroglycerin (spray or tablet) and buccal or sublingual glucose preparations are the common prehospital examples.

Parenteral Routes

Intramuscular (IM)

Deposits drug into well-perfused skeletal muscle for absorption via the capillary bed. Onset is 10 to 20 minutes and absorption depends entirely on perfusion, so it is unreliable in shock.

Technique: 21–25 gauge needle, 90-degree angle, length chosen so the drug reaches muscle and not subcutaneous fat, skin cleaned and allowed to dry, and the site documented.

Subcutaneous (SC)

Into the loose connective tissue beneath the dermis — outer upper arm, anterior thigh, or abdomen. Small volumes only (generally up to about 1 mL), 25–27 gauge needle, 45- to 90-degree angle depending on tissue depth. Onset 15 to 30 minutes and highly unreliable in shock. Rotate sites in patients who inject regularly, as lipohypertrophy impairs absorption.

Intravenous (IV)

The fastest and most reliable route, with 100% bioavailability and no absorption phase. Cannulation technique, site selection, and maintenance are covered in Section 19.1.

• Once given, it cannot be retrieved — which is why the rights and the independent double check matter most here.
• Give at the rate the drug requires; rapid push of some drugs causes hypotension or dysrhythmia.
• Flush after each drug, particularly in cardiac arrest, where a 20 mL flush with limb elevation moves the drug from a peripheral vein into the central circulation.
• Check patency and watch the site: extravasation of an irritant such as D50W causes tissue necrosis.

Intraosseous (IO)

Into the medullary cavity, a non-collapsible venous plexus that drains directly into the central circulation. Onset and dosing are equivalent to intravenous. Covered in Section 19.2.

Intranasal (IN)

Delivered as a fine mist through a mucosal atomization device onto the highly vascular nasal mucosa, from which some drug also reaches the central nervous system directly along the olfactory route.

• No needle, so it is fast to deploy, safe in an agitated or seizing patient, and eliminates sharps risk — the principal reason naloxone and midazolam are commonly given this way.
• Split the dose between both nostrils — each nostril absorbs a limited volume, generally about 0.5 to 1 mL, and exceeding it means the excess is swallowed and wasted.
• Use a concentrated formulation so the volume stays small.
• Reduced effectiveness with epistaxis, copious mucus, nasal trauma, prior use of a vasoconstrictor spray, or septal disease.

Endotracheal (ET)

Instillation of certain drugs down an endotracheal tube for absorption across the alveolar membrane. Absorption is erratic and unreliable, higher doses are required, and it is a last resort used only when no intravenous or intraosseous access can be obtained and only for the limited set of drugs that tolerate it. It is listed in skill #32 as knowledge, not as a preferred technique.

Inhalation

Delivery of an aerosolized or nebulized drug to the respiratory mucosa and alveoli for rapid local and systemic effect. Note that skill #32 specifies inhalation not including oxygen — oxygen administration is covered separately under skills #22 and #23.

• Nebulizer: drug is driven by gas flow, typically 6 to 8 L/min, into a mist. Requires only tidal breathing, so it works in a distressed patient. Common prehospital use: salbutamol, with or without ipratropium.
• Metered-dose inhaler with a spacer: as effective as a nebulizer for most patients when technique is correct, faster to deploy, and does not aerosolize as much. Requires coordination or a spacer with a mask.
• Effectiveness depends on tidal volume and flow. A patient too exhausted to generate flow will not receive the drug; that patient needs assisted ventilation, through which the nebulized drug can often be delivered in line.
• Aerosol-generating — a point-of-care risk assessment governs the protective equipment used (Section 8.4).

Topical and Transdermal

Applied to skin or mucous membrane for local effect or, with transdermal formulations, for systemic absorption through the skin.

• Wear gloves. Self-administration by absorption through the paramedic's own skin is a real and documented hazard with nitroglycerin paste and fentanyl patches.
• Absorption rises with heat, broken skin, and increased perfusion — a patient with a fentanyl patch who becomes febrile or is actively warmed can absorb substantially more drug.
• Remove existing patches when they may be contributing to toxicity, document removal, and account for the patch — and check for a patch in any unexplained decreased level of consciousness, including on the back, under breast tissue, and between skin folds.
• Do not place defibrillation pads over a medication patch. Remove the patch, wipe the area, and then apply the pad; the metallic backing on some patches can arc and cause burns.

[!TIP] Three route errors recur on examinations. First, 1:1,000 epinephrine is never given intravenously as a bolus in anaphylaxis — it is intramuscular into the anterolateral thigh. Second, nothing goes in the mouth — not glucose gel, not a sublingual tablet — for a patient who cannot protect their airway. Third, intramuscular and subcutaneous absorption fails in shock, so a patient who is poorly perfused needs an intravenous or intraosseous route for any time-critical drug.