basic pharmacology

Basic Pharmacology
Introduction
Pharmacology is the study of drugs. Drug are defined as chemical substances that have an effect on a living
organism; medicines are drugs used to prevent or treat disease. The administration route, health and age of the
patient, and the chemical structure of the drug all play a role in how fast it will act. A drug is considered effective
if it elicits the desired therapeutic response with minimal side effects.
ALL drugs elicit more than one response and the use of multiple drugs at the same time may lead to desirable
or dangerous drug interactions. Fortunately, due to effective drug control laws, the desired therapeutic response
usually occurs and the side effects of most official drugs are predictable, minimal and can be reduced by adjusting
the dose of the drug. That-being-said, a few patients experience side effects strong enough to warrant discontinuing
the drug treatment regime. Unlike most side effects, systemic allergic reactions are unpredictable and while most
result in hives some cause respiratory distress, vascular collapse, and death. Interactions between multiple drugs
taken concurrently may result in either an increase or decrease of one or both drugs due to changes in each drug’s
absorption, distribution, metabolism, or excretion (ADME) characteristics. The majority of drug interactions are
known and can be prevented by checking the appropriate data base. Patients taking any form of drug should be
monitored for side effects, systemic allergic reactions, and drug interactions (if taking more than one drug).
Drug Classifications
Drugs fall into two distinct categories: those that require a physician’s prescription to obtain (Rx) and those
that can be purchased over-the-counter (OTC).
Within these categories they are further classified by the body system they effect, how they are used, or how
they elicit their response. Drugs may be referred to by their chemical names, official names, brand names, or by
their generic names. Because it describes the drug’s exact molecular structure the chemical name is complex and
really only useful to chemists. Upon approval the Federal Drug Administration (FDA) gives each drug an official
name. Trademark or brand names are proprietary and assigned and registered by the drug’s manufacturer. In order
to distinguish them from generic names, official drug names and brand names are capitalized when in print. The
generic name is non-proprietary, simpler, and not capitalized when in print. In order to avoid confusion ALL drugs
in this book are referred to by their generic names.
How Drugs Work—An Conceptual Overview
Most drugs act by forming chemical bonds with specific receptor sites within the body to stimulate and/or
inhibit a response. While drugs alter the body’s physiologic activity along existing chemical pathways, they DO
NOT create new pathways or responses. The success of a drug’s response depends on two factors: it’s molecular
fit and the number of receptor sites it bonds to. The better the fit and the greater number of receptor sites occupied,
the stronger the response. In order for drugs elicit a response they must first be dissolved in the patient’s blood
or plasma and then transported to their respective receptor sites. Once dissolved, they go thorough four distinct
stages absorption, distribution, metabolism, and excretion (ADME).
Absorption is the process by which a drug is transported from its administration site into general circulation.
The rate of absorption depends on the patient’s hydration status, the administration route, the blood flow through
the tissue at the administration site, and the solubility of the drug.
Once absorbed most drugs bind to—and are carried by—plasma proteins in the blood and lymph for distribution.
When bound, the large size of the resulting drug/protein complex prevent the drug from crossing the vascular
membranes into the tissue; and a drug MUST cross into tissue to bathe receptor sites, become metabolized by
the liver, or be excreted by the kidneys. Furthermore, once in the extra cellular space, fat soluble drugs are likely
to bind to fat cells rendering them temporally inactive. As serum drug levels change due to a drug response, metabolism,
or excretion, molecules of the bound drug are released from the drug/protein complex and/or fat cells to
maintain the equilibrium between the free and bound drug. It is only the unbound drug in solution that is pharmacologically
active. The amount of the drug that reaches the receptor sites determines the strength of its response.
Recptor Site (Lock)
Drug (Key)
Agonist Antagonist Partial Agonist
An agonist bonds and fits well enough into the recptor
site to elicits a strong response. An antagonist bonds but
does NOT fit well enough to elicit a response. A partial agonist
bonds but only fits well enough into the site to elicit a
partial response. As long as a site is occupied other drugs
are prevented from bonding to the same site.
Lock & Key Principle of Drug Action
Serum levels of the drug MUST remain within a specific range in order to render the desired therapeutic effect.
Enzymes produced by the liver are the body’s primary way of breaking down drugs and preparing them for
removal (metabolism). Once inactivated, drug metabolites—and in some cases the active drug—are excreted
from the body primarily through the urinary system and kidneys. Other less utilized removal methods are via the
GI tract (bile), lungs (exhalation), and skin. Age, disease, smoking, and dehydration may decrease liver and renal
function slowing both drug metabolism and excretion.
Drug/Plasma Protein Complex
Drug Bound to Fat Celll
Free Drug
Drug Recptor Site
Drug in
Circulation
Drug in Tissue
Drug Administration in a Wilderness Environment
Drugs are administered by one of three routes: through the digestive system via ingestion, directly into
the body’s fluid reservoir via injection, and through body membranes via the lungs, mucus membranes, or skin.
Choosing and administering a drug in a wilderness context by non-physicians should be done only in specific
circumstances and according to protocols established by the expedition’s—or organization’s—physician advisor.
Hydration, even in healthy people, is always a concern in a wilderness environment and becomes even more so
when administering drugs. Because dehydration equals poor absorption, distribution, metabolism, and excretion
(ADME) and inhibits the desired therapeutic response, make sure that your patient is well-hydrated before administrating
any drugs.
Because oral drugs are effective, easy to carry, and simple to administer, they tend to make up the majority
of the drugs carried in an expedition first aid kit. Before an oral medication can reach general circulation it must
survive the acids and enzymes of the digestive system, be successfully transported across the stomach or intestinal
lining, and survive the initial pass through the liver. Throughout the process hydration is extremely important;
even in a well-hydrated patient oral medications should be given with water (8 oz minimum).
The skin and mucus membranes are another common drug administration route used in a wilderness setting
because, like oral drugs, they are effective, easy to carry, and simple to administer. Ear and eye drops are used to
treat local infections as are vaginal suppositories. Rectal suppositories are used to treat constipation. Topical skin
ointments are used to treat local allergic reactions, promote healing in partial thickness wounds, treat a variety
of sub-cutaneous fungal infections. Sub-lingual or buccal glucose tablets are used to treat hypoglycemia in the
insulin dependant diabetic and sub-lingual tablets are used to treat angina.
Absorption via inhalation is influenced by the depth of the patient’s respirations. Absorption in the lungs is
more effective when a spacer is used to disperse the medication prior to inhalation and the patient can take a deep
breath and hold the drug in their lungs for a few seconds before exhaling. In a wilderness setting the inhalation
route tends to be reserved for participants suffering from asthma.
While all types of injections bypass the digestive system and frequently offer the fastest absorption and
distribution route, they should NOT be the first choice for a expedition first aid kit because they are expensive,
difficult to carry, and require advanced training to use. Subcutaneous (SC) and intramuscular (IM) injections
of epinephrine are commonly given—primarily by auto-injectors—to treat systemic allergic reactions, Because
there are more blood vessels in muscles than in subcutaneous tissue, absorption is faster via IM injection. Give
IM injections in the muscle belly where blood flow is the greatest and there are no large arteries or veins; the most
common sight used in the field is the anterior thigh. While intravenous (IV) injections provide the most direct
route to the blood, IV solutions and kits are rarely carried due their relatively high weight, low need, storage problems,
difficulty of administration in challenging environments, and the high level of training needed to administer
them correctly even under the best of circumstances. Intraosseous (IO) or bone injections are similar to IVs in that
they require specialized equipment and training but are easier to use in hazardous environments. Both IV and IO
injections tend to be reserved for inbound rescue teams who respond with field paramedics, nurses, or physicians
and have the capacity to carry a lot of gear.
When choosing a drug, make sure that you:
• adhere to your protocols
• review the patient’s history for prior systemic allergic reactions to the drug
• there is no possibility of dangerous drug interactions if multiple drugs are to be given
• review and advise the patient of the possible side effects
Prior to administration, assess and document the patient’s response to any prior medications and make sure
they are hydrated. Make sure you have the:
• Right patient
• Right dru
• Right administration route
• Right dose
• Right time
After administering the drug, document all of the above in the patient’s SOAP note and/or a separate drug log.