Wilderness EMS Pharmacology

Nancy Pietroski

PHARMACOLOGY BASICS FOR WILDERNESS EMS

One of the hallmarks of EMS (the formal delivery of health care in the field) versus ad hoc first aid care is access to pharmaceutical treatments. While many factors may limit the range of medications available to a wilderness EMS (WEMS) provider, it still represents an important potential element of WEMS practice. This chapter is not intended to be an in-depth discussion of the principles of pharmacology. Standard pharmacology texts can be consulted for a more comprehensive treatment of the subject. The chapter’s focus will be the use of medications in a WEMS setting. It will include basic pharmacological principles as they are relevant to the use of drugs and medications in this environment.

The terms “drug” and “medicine” or “medication” are used interchangeably in standard EMS texts, standards, and protocols. A medicine is a drug, substance, compound, or preparation taken for prevention or treatment of disease. A drug, according to the Food, Drug, and Cosmetic Act, is a substance recognized in an official pharmacopoeia or formulary; a substance intended for use in the diagnosis, cure, mitigation, treatment, or prevention of disease; or a substance other than food intended to affect the structure or function of the body.¹

Pharmacology is the science of drugs, dealing with the origin, nature, chemistry, effects, and uses of drugs. Pharmacology includes pharmacokinetics, the study of the fate of drugs in the body (ie, what the body does to the drug), and pharmacodynamics, the study of the biochemical and physiological effects of drugs on the body and the mechanisms of their actions (ie, what the drug does to the body).

Pharmacokinetic Processes

Pharmacokinetic processes include absorption, distribution, metabolism, and excretion (Figure 11.1).

Absorption

Absorption is the process of drug movement from the site of absorption toward the systemic circulation. The route of drug administration affects the rate and extent of absorption. Drugs administered enterally (via the gastrointestinal [GI] tract) must go through an absorption phase. This may be affected by the rate of gastric emptying, the presence of food or other drugs in the stomach, and the formulation of the drug (eg, a sustained-release formulation is released into the bloodstream more slowly). Drugs that are administered parenterally do not go through this absorption phase through the GI tract. Figure 11.2 displays various routes of parenteral administration. With orally administered drugs, there is also the phenomenon of the first-pass effect, where drugs pass through portal (liver) circulation before reaching blood, thereby limiting the extent of absorption by reducing the amount of unchanged drug that enters the bloodstream.

Distribution

The distribution of a drug represents its diffusion throughout the body, usually via blood with ultimate delivery to various organs and tissues. Factors that affect drug distribution include blood flow to tissues and organs and the lipid (fat) solubility of the drug, determined by its chemical structure. For example, a highly lipid-soluble drug will penetrate into central nervous system tissue, which has a higher lipid content than blood. Highly lipid-soluble drugs will also cross the placental barrier, which could potentially cause harm to the developing fetus.

Figure 11.3 illustrates a blood concentration-time curve and various routes of administration of drugs. Note that intravenous administration results in immediate absorption of drug into the bloodstream, high concentrations, and a fairly rapid fall in concentration. Intramuscular administration has delayed absorption (depends on blood flow through muscle) and a slower fall in concentration. Oral administration has an even more delayed absorption and slower fall in concentration.

FIGURE 11.1. Pharmacokinetic processes.

Metabolism/Excretion

Metabolism is the chemical transformation (biotransformation) of the drug into another form (eg, parent drug to metabolite). The majority of drug metabolism takes place in the liver. Cytochrome P450 enzymes are important when considering drug interactions, as many drugs are metabolized by these liver enzymes and may interfere with each other, potentially resulting in antagonistic (opposing), additive (increased results), or synergistic (enhancing) effects. Patients with hepatic impairment may be at risk of toxicity if a drug is largely metabolized by the liver, and dose adjustment may be necessary. It is essential to take a drug history before administering any new medication to patients. This allows the provider to be aware of any potential drug interaction and how to avoid or mitigate such interaction. Most drugs are eliminated by the kidneys via urine; patients with renal impairment may be at risk of toxicity if the dose of renally excreted drugs is not adjusted. Other possible routes of
drug elimination are skin (perspiration), lungs (respiration), breast milk, and bile/feces.

FIGURE 11.2. Various routes of parenteral administration. Reprinted from Stein SM. Drug administration. In: Boh LE, ed. Pharmacy Practice Manual: A Guide to the Clinical Experience. 2nd ed. Philadelphia, PA: Lippincott Williams & Wilkins; 2001.

FIGURE 11.3. Blood concentration-time curve.

Pharmacokinetics: Route of Drug Administration

EMS Setting

Table 11.1 lists the different routes of administration for drugs that may be used in the EMS setting, and the practice level for which the route is approved. This is a guide only; protocols vary by state and may differ, so always follow local protocol. Preferred routes of administration for the wilderness EMS setting will be discussed later in the chapter.

The intracavitary, intrathecal, intralingual, and umbilical routes are other possible routes of drug administration, but are used extremely rarely, and are only available on a clinician level. Some drugs are administered via nebulizer, but the equipment needed for this is not likely to be used in WEMS.

Drug Formulations

Table 11.2 lists the major formulations in which drugs are available depending on the route of administration. Note that “parenteral” encompasses a number of routes listed in Table 11.1. There may be advantages or disadvantages to certain formulations in a wilderness setting and these are noted. Figures 11.4, 11.5, 11.6, 11.7, 11.8 illustrate various drug formulations.

Table 11.1 Major Routes of Drug Administration in the EMS Setting²^,³^,⁴^,⁵^,⁶^,⁷^,⁸^,⁹

Route	Description/ Formulations	Rate of Absorption	Advantages/ Disadvantages	Practice Level^a
Oral (PO)	By mouth	Slow; through GI tract	Patient must be conscious, able to swallow	FA (assist) EMT (assist) EMD (assist) AEMT Paramedic Clinician
Orogastric (OG)	Directly into stomach via tube in mouth	Same as oral	If patient unable to swallow	Paramedic Clinician
Nasogastric (NG)	Directly into stomach via tube in nose	Same as oral	If patient unable to swallow	Paramedic Clinician
Buccal/Sublingual (SL)	Drug placed on oral mucosa (between cheek and gum) or under tongue (drug must be formulated for this)	Fast; avoids first-pass	Patients must be conscious and alert or may choke	FA (assist) EMT (assist) AEMT Paramedic Clinician
Intravenous (IV)	Into vein (by needle)	Gets directly into bloodstream; 100% absorption	Can’t establish access (eg, dehydration); drug extravasation	AEMT (fluids only) Paramedic Clinician
Intraosseous (IO)	Needle inserted into bone, gets into vein (proximal tibia/popliteal; femur/femoral); distal tibia (medial malleolus)/great saphenous; proximal humerus/axillary; manubrium (sternum)/internal mammary and azygos	Same as IV	Use when IV cannot be established, hypovolemia/hemodynamic instability, GCS<8, respiratory failure; cannot use in fractured bone⁷	AEMT (pediatric only) AEMT (may be limited) Paramedic Physician
Intramuscular (IM)	Into muscle (use 22-25-gauge needle; 5/8-1.5 in depending on age, size of patient)	Slower rate than IV; depends on blood flow and which muscle (deltoid, gluteus, thigh) Not as effective in shock (decreased blood flow to muscles)	When IV access cannot be obtained; prolonged serum levels; less effective in low muscle mass (elderly, malnourished) or diabetics; can cause pain, hematoma (use lidocaine)	AEMT Paramedic Physician Some states permit FA, EMR, EMT via auto-injector
Subcutaneous (SC)	Under the subcutaneous layer of skin (use 23-25-gauge, 5/8-inch, needle); <2 mL volume	Slower than IV, but fairly rapid	When oral administration is difficult or not feasible (some pain, nausea/vomiting meds, insulin)	AEMT Paramedic Clinician
Intradermal	Under dermal layer of skin (use 26-28 gauge; 3/8-3/4 inch); <1 mL volume	Slower than IV	May be advantageous for some vaccines (eg, rabies if in short supply)	Paramedic Clinician
Rectal	Via rectum	Rapid, but can be unpredictable	When cannot be taken orally	EMT, AEMT can assist Diastat (some states) Paramedic Clinician
Intranasal	Spray	Rapid; high drug levels; avoids first-pass	No needle	AEMT Paramedic Clinician
Dermal (topical)	Cream, ointment, spray, etc.	Slower absorption; local effect	Convenient	FA EMT AEMT Paramedic Clinician
Transdermal	Through the skin (patch)	Slower absorption	Convenient; sustained release	Paramedic Clinician
Inhalation	Goes directly into lungs (eg, MDI)	Rapid; gets directly to lungs	Effective	FA (assist with MDI) EMR (assist with MDI) EMT (assist with MDI) AEMT Paramedic Clinician
Otic	Into ear	Local effect	Specifically for ear	Clinician
Ophthalmic	Into eye	Local effect	Specifically for eye	Clinician
Vaginal	Into vagina	Local effect	Systemic absorption possible	Clinician
Intra-articular	Into the joint	For local effect	Rarely used in EMS except by specialists	Clinician
Endotracheal	Via endotracheal tube (use only if IV or IO access cannot be established)	Need 2.5× IV dose	Lidocaine, epinephrine, atropine, naloxone, vasopressin	Paramedic Clinician
FA, first aid; EMD, emergency medical dispatcher; EMR, emergency medical responder; EMT, emergency medical technician; AEMT, advanced emergency medical technician; EMS, emergency medical services; GI, gastrointestinal; GCS, Glasgow Coma Scale; MDI, metered dose inhalers.
^aNote that “Practice Level” are general national standards in the United States. These may vary by local or state practice or legislation and are intended merely to be a guideline.

Table 11.2 Drug Formulations

Route	Formulation(s)	Advantages/Disadvantages in Wilderness Setting
Oral	Capsules, tablets, sublingual tablets, buccal tablets, orally disintegrating tablets, powder (to be mixed with water), syrup, solution, drops, troche, tincture, suspension, spirit, elixir, emulsion	Capsules may be less likely to break than tablets Unit dose packaging protects the contents Powder that needs to be mixed is lighter than a bottle of liquid, but clean water must be used to reconstitute
Parenteral	Single dose vial, multidose vial, syringe, prefilled syringe (eg, Tubex), ampule, bag	Single dose vial may be less prone to medication errors Multidose vial may conserve space; should contain a preservative Ampules may crack
Topical	Cream, ointment, gel, paste, solution, drops, tincture, spray, patch	Some formulations are more susceptible to extremes of temperature (discussed later in the chapter)
Rectal	Suppository, enema	Suppositories more convenient
Inhalation	Metered dose inhaler, spray, nebulizer	Metered dose inhalers are convenient
Intranasal	Spray	Some drugs in intranasal form are more susceptible to extremes of temperature (discussed later in the chapter)
Otic	Solution, suspension, drops	Suspensions must be shaken
Ophthalmic	Solution, suspension, drops	Suspensions must be shaken
Vaginal	Cream, ointment, suppository	Some formulations are susceptible to extremes of temperature (discussed later in the chapter)

FIGURE 11.4. Various oral drug formulations. (Left to right, top) Tablets, caplets, and enteric-coated tablets. (Bottom) Capsules, gel-caps, chewable tablets, and troche. Photo by Caroline Bunker Rosdahl. In: Rosdahl CB and Kowalski MT. Textbook of Basic Nursing. 11th ed. Philadelphia, PA: Wolters Kluwer; 2017.

Pharmacodynamics

Pharmacodynamics is the study of what a drug does to the body, or the way it exerts its clinical effects, also known as the mechanism of action (MOA). The MOA of drugs may involve receptor interactions (inhibition or stimulation) or enzyme interactions (inhibition or stimulation).

FIGURE 11.5. Powder for oral suspension (powder that needs to be mixed is lighter than a bottle of liquid, but clean water must be used to reconstitute). From Kronenberger J, Ledbetter J. Lippincott Williams & Wilkins’ Comprehensive Medical Assisting. 5th ed. Philadelphia, PA: Wolters Kluwer; 2016.

FIGURE 11.6. Ampule, vial, and prefilled syringe (clockwise from top left). Courtesy of B. Proud. In: Taylor C, Lillis C, Lynn P. Fundamentals of Nursing. 6th ed. Philadelphia, PA: Wolters Kluwer; 2006.

The body’s endogenous hormones or neurotransmitters interact with receptors to produce pharmacological activity; drugs are exogenous compounds that are structurally similar to these endogenous compounds and may produce similar pharmacological effects. Similarly, enzymes are proteins produced endogenously that catalyze chemical reactions within or outside of cells; drugs are designed to alter enzymes by blocking an enzyme (inhibitor) or by stimulating an enzyme (inducer).

After a drug is administered, its clinical effects can be described in humans as a specific drug response curve, encompassing maximal (peak) effects and minimal (trough) effects. Increased dosages of a drug produce an increased effect to a certain level, at which no further beneficial effect is attained with any higher dosage. If that level is exceeded, an adverse effect (adverse reaction) may occur. A side effect is a nuisance effect that is annoying but not dangerous, whereas toxicity of a drug is a potentially harmful or even fatal effect, and is usually dose-related. A non-dose-related adverse effect can occur at high or low dosages, with the first dose or after a period of time, and is typically an allergic reaction.

Special Populations

There are certain populations in which the pharmacokinetics and pharmacodynamics of a drug may be different than in a healthy adult.

Pediatrics

Infants and children should not be thought of as merely smaller adults, as the pharmacokinetic processes may be different depending on age. The U.S. Food and Drug Administration (FDA) requires that drugs be studied specifically in pediatrics to determine efficacy and safety and the most optimal dosing.¹⁰
Many drugs in pediatrics are dosed based on weight or body surface area, and pediatric dosage guidelines must be consulted before administration of medications in this population. The Broselow Pediatric Emergency Tape (often simply known as “Broselow Tape,” seen in Figure 11.9), a color-coded tape measure that relates a child’s height to their weight, is a useful tool for calculating pediatric dosages of drugs, in addition to size of emergency equipment and voltage for an automated external defibrillator. As well, some pediatric patients may not be able to swallow pills, so instead of a solid oral dosage formulation, they will need an oral liquid, granules, or other route of administration.

FIGURE 11.7. A, Multidose vial. B, Multidose vial label (note the preservative benzyl alcohol, needed for multidose).

FIGURE 11.8. Metered dose inhaler.

Geriatrics

There are age-related changes in handling of drugs, especially a decrease in renal function, so the dose of renally excreted drugs may need to be adjusted, although this will not be able to be measured in the field. The elderly are more prone to dehydration, which will also impact the renal handling of drugs. They are also more likely to have an increase in the number of comorbid conditions, and may be taking numerous medications (polypharmacy), so drug interactions must be taken into consideration when administering a new medication.

Pregnancy/Labor and Delivery/Nursing

It is essential to know if the patient is or could possibly be pregnant or is breastfeeding before administering a drug. The FDA issued the “Pregnancy and Lactation Labeling Rule” in late 2014, which removed the former pregnancy categories of A, B ,C, D, and X that health care professionals were familiar with, but often found complex and confusing.¹¹ The new rule provides simplified guidelines for drug manufacturers to summarize the risks of using a drug during pregnancy and lactation. The “Pregnancy” and “Lactation” sections of the prescribing information should be consulted before administration of any drug in pregnancy.

FIGURE 11.9. Broselow tape. Used for calculating pediatric dosages of drugs. (From Ricci SS, Kyle T, Carman S. Maternity and Pediatric Nursing. 3rd ed. Philadelphia, PA: Wolters Kluwer; 2017.)

Renal Impairment

While renal impairment will not be assessed in the field, dehydration and shock can lead to renal dysfunction and decreased excretion of renally processed drugs, so this must be kept in mind when administering these medications (See Box 11.1 for tips on taking a Drug History).

ADMINISTERING DRUGS IN A WILDERNESS ENVIRONMENT

The previous section provided a foundation for understanding the basic pharmacology of drugs, including the different routes of administration and how they may differ for WEMS providers, and reviewed the importance of taking a drug history. This section will focus on what factors to consider when administering drugs in a wilderness environment, the effect of different environmental conditions on medication use, and the effect of these environmental conditions on the storage and stability, and expiration dating of medications.

The “Rights of Medication Administration” in a Wilderness Setting

The “Rights of Medication Administration” are ingrained in all health care processes. In a wilderness setting, some of the “Rights” may be more or less pertinent than in a traditional emergency or institutional setting, as seen in Table 11.3. These “Rights” need to be followed for over-the-counter (OTC) drugs as well.

Table 11.4 lists important principles for medication use in a wilderness EMS setting.

Drug Information

It is important to be fully informed about the drugs that are carried in a medical kit and are being administered. It is important to be familiar with brand (trade) and generic names, because a drug may be available as the generic version but is still referred to by the brand name, for example, Cipro (ciprofloxacin). Also be familiar with a drug’s indications, dosage and administration, dosage forms and strengths, contraindications/warnings/precautions, adverse reactions, drug interactions, use in different populations such as children and pregnancy, and safe storage and handling considerations.

Be aware that any information that comes from the drug prescribing information is considered on-label. Drugs can also be used off-label, which means that the drug is used for an indication, route, dose, or dosage form that is not specified in the prescribing information.¹² Off-label use may be common in WEMS, but should always be done under the direction of a physician. See Chapter 5 on the legal implications of this practice.

Table 11.5 lists examples of sources of drug information for EMS providers in a traditional setting, and those that are more specific for WEMS. Local EMS protocols also contain detailed information about drug administration and safety considerations. A drug information source should be considered an integral part of the medical supply kit as it is often difficult to remember dosing schedules, drug interactions, and similar details in a stressful environment.

Effect of the Wilderness Environment on Medication Use

Different environmental conditions can have an effect on preexisting medical problems, or on medications that are already being taken by a person for a medical condition. As well, certain medications that are taken can exacerbate environmental conditions. The effect on preexisting medical problems, such as multisystem trauma, blood loss, shock, vomiting/diarrhea, moderate to severe burns, fever secondary to infection (all of which can lead to dehydration), and hyper/hypothermia will be discussed in further detail in Chapter 22.

Table 11.6 presents the effect of some environmental conditions on medications already being taken, or those medications exacerbating environmental conditions.¹³^,¹⁴^,¹⁵^,¹⁶^,¹⁷^,¹⁸

Drug Storage and Stability in the Wilderness Environment

This section will discuss the effect of different environmental conditions on the storage and stability of drugs, an important factor to consider especially when traveling at extremes of temperature. In the examples of the different environments above, proper storage conditions for drugs may not always be easily met.