10 Pharmacology and Medication Safety

Start with the clinical decision

Medication therapy is a clinical decision, not simply a calculation. Before administration, connect the patient’s presentation to the medication’s intended effect, likely risks, route, and expected response.

Authorization, scope of practice, and permitted doses can vary by jurisdiction. Follow current local protocols, medical direction, and product labeling. National model guidelines can inform EMS systems, but they do not replace local protocols.

Relate drug effects to the patient

Pharmacodynamics describes what a drug does to the body, including intended and adverse effects. Pharmacokinetics describes what the body does to a drug: absorption, distribution, metabolism, and elimination. Onset, peak effect, and duration depend on the drug and route.

A rapidly acting intravenous medication can produce a prompt effect, but may also cause an abrupt adverse response. Oral drugs generally have slower and less predictable absorption in an acutely ill patient.

Choose a medication only when its indication fits the assessment. Consider age, weight, pregnancy status when relevant, allergies or prior reactions, medical history, vital signs, current medications, and the patient’s ability to use the route safely. Distinguish an Absolute contraindication from a Precaution: some therapies may have no absolute contraindication in an immediately life-threatening situation, while still requiring careful monitoring and protocol-compliant use.

Calculate doses and volumes

Use consistent units and write out each calculation. First identify whether the order is a fixed dose, a weight-based dose, a concentration, or a dose rate. Milligrams $(\text{mg})$ measure drug amount; milliliters $(\text{mL})$ measure liquid volume. Do not confuse the two.

Core calculations

Use the appropriate relationship, converting units consistently before calculating:

For example, if the ordered dose is $25\,\text{mg}$ and the vial contains $50\,\text{mg/mL}$, the volume is:

For a protocol example specifying $0.1\,\text{mg/kg}$ for a $20\,\text{kg}$ patient, the dose is $2\,\text{mg}$. At a concentration of $1\,\text{mg/mL}$, the volume is $2\,\text{mL}$. These are calculation examples, not treatment recommendations; use the authorized indication, dose limits, and actual product concentration.

Convert pounds to kilograms by dividing by $2.2$. Check for a maximum dose, repeat interval, or cumulative limit. For pediatric patients, use a reliable weight or an approved length-based tool as directed, and independently verify the resulting dose and volume. A second clinician check is especially useful for high-risk drugs, pediatric doses, infusions, and calculations involving concentration changes.

Choose and verify the route

The route is part of the medication order. Each route has practical considerations:

• Oral (PO): Convenient, but avoid when swallowing is unsafe or consciousness is impaired; absorption may be delayed.

• Sublingual (SL): Absorbed through the oral mucosa. Confirm that the patient can follow instructions and that protocol conditions are met.

• Buccal: Placed between the cheek and gum. If the product requires mucosal absorption, avoid swallowing or chewing it.

• Intramuscular (IM): Useful when rapid access is needed and intravenous access is unavailable or inappropriate. Select a suitable site and needle length.

• Subcutaneous (SC): Absorption can be slower and less predictable when perfusion is poor.

• Intravenous (IV) and intraosseous (IO): Provide systemic access. Verify patency, compatibility, concentration, and administration rate; monitor closely for extravasation and adverse effects.

• Inhaled or nebulized: Delivers medication to the respiratory tract. Check equipment function, patient tolerance, and response.

• Intranasal (IN): Can avoid needle access. Use the correct device and concentration, and account for product volume limits and possible impaired absorption.

• Topical or transdermal: Generally has a slower onset. Inspect for existing patches and prevent unintended exposure.

Do not substitute routes, crush or split a formulation, mix drugs, or use an alternative concentration unless permitted by the protocol, product instructions, or medical direction.

Screen for contraindications and interactions

Screen for allergies and ask about the specific reaction. A reported side effect is not always an allergy, but a serious prior reaction matters. Check for duplicate ingredients, recent doses, medication patches, and drugs the patient has taken. A Medication interaction can increase toxicity, intensify an intended effect, or reduce treatment effectiveness. When uncertain, consult the protocol, an approved drug reference, or medical direction rather than guessing. FDA drug labeling includes indications, dosing, contraindications, warnings, adverse effects, and interactions.

Apply risk checks to common examples

• Nitroglycerin: Assess blood pressure and relevant history; hypotension is a major safety concern. Ask about recent phosphodiesterase-5 inhibitor use because the combination can cause severe hypotension. Follow the exact protocol criteria.

• Aspirin: Check for serious allergy, active bleeding, and other protocol-specific exclusions.

• Opioid analgesics: Reassess ventilation, oxygenation, mental status, and hemodynamics. Benzodiazepines, alcohol, and other sedatives can compound respiratory and central nervous system depression.

• Oral glucose: Use only when the patient can protect the airway and swallow safely; choose another authorized approach if not.

• Adenosine: Rhythm recognition and hemodynamic status matter. Certain irregular rhythms and wide-complex tachycardias require special caution and protocol-directed judgment.

• Epinephrine for anaphylaxis: Prompt treatment of a life-threatening allergic reaction is critical. Do not delay indicated treatment while searching for a blanket prohibition that does not exist; use the correct product, concentration, route, and protocol.

Contraindications and interactions depend on the drug and situation; these examples do not replace protocol criteria or product labeling. In cardiac arrest, medication timing and selection are algorithm-dependent. For example, current AHA adult arrest guidance places epinephrine and antiarrhythmic therapy within the resuscitation sequence rather than as stand-alone interventions.

Administer safely and reassess

Use a deliberate check before every administration:

1. Right patient: Confirm identity as circumstances allow.

2. Right medication and indication: Match the drug to the clinical problem and protocol.

3. Right dose: Verify units, weight basis, concentration, maximum, and prior doses.

4. Right route and time: Confirm that both are authorized and appropriate now.

5. Right preparation and documentation: Inspect the label, expiration, appearance, compatibility, and delivery device; document what was given and the response.

Use the generic drug name when possible. Read the label rather than relying on package color or memory, and verify concentration, especially when similar products or different strengths are carried. Reduce interruptions during preparation, label syringes when needed, and use an independent double-check for high-risk calculations. A Medication error is a preventable event that can lead to inappropriate use or patient harm. Report errors and near misses according to agency policy so hazards can be addressed.

Obtain relevant baseline findings before administration. Afterward, reassess the intended effect and potential adverse effects at intervals appropriate to the medication and patient. If the patient worsens, stop or withhold further doses when appropriate, support airway, breathing, and circulation, treat complications within protocol, and seek medical direction. Document the indication, dose, route, time, relevant assessment, response, and any adverse event.

Safe pharmacology combines a fitting clinical indication, patient-specific risk assessment, accurate unit-based calculation, correct route, and monitoring. Verify the medication and concentration, screen for contraindications and interactions, follow local protocol, and reassess after every dose. When uncertain, pause and verify rather than estimate.