Principles of Drug Actions

Covers Slides 1–38: Patient identifiers & medication verification, drug administration phase, routes of administration, pharmacokinetic phase, pharmacodynamic phase, lock and key theory, adrenergic pathway, and cholinergic pathway.

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Principles of Drug Actions

Introduction: Definition

Pharmacology — the study of drugs to include their origin, properties, and interactions with living organisms.

Drugs are often referred to by their generic and trade (brand) name:

  • Acetaminophen / Tylenol
  • Ibuprofen / Motrin or Advil

Patient and Medication Verification

BEFORE we administer any medication, we must first be sure we have the right patient!

Step 1: Verify Patient Identity

Verify patient identity using 2 identifiers: Full name and DOB.

Step 2: Verify the Medication

Verify the medication prescribed and double check if any substitutions are or are not allowed.

Example: Your patient was prescribed albuterol. The patient states that albuterol makes their heart race. The physician did not list any approved substitutions. What do we do?

Step 3: Verify the Dosage

Verify the dosage of the medication. The dosage of the drug can vary depending on the condition being treated and the way it is administered to the patient.

Step 4: Verify Correct Treatment Frequency

How many times can this drug be given within a 24-hour period? Are we giving it during the correct prescribed time?

Step 5: Verify Treatment Route

Example: Your order states to give your patient a dry powder inhaler (device that crushes the pill and is released when the user inhales deeply through the mouthpiece). You go to your patient's room and see that they are intubated. What now?

Phases of Drug Action

  1. Administration
  2. Pharmacokinetics
  3. Pharmacodynamics

Administration

Administration — how the drug is made available to the body.

Routes of Administration

  1. Oral
  2. Parenteral (injectable) — Intravenous (IV), Intramuscular (IM), Subcutaneous (SC), Intraosseous (IO)
  3. Inhalation
  4. Topical

Oral Route

  • Preferable for patients who cannot tolerate or may not respond to inhaled medications
  • Noncompliant patients
  • Children
  • Slower absorption time
  • Metabolized systemically; greater side effects

Inhalation Route

  • Produces less side effects since it bypasses GI absorption and limits hepatic metabolism
  • Requires smaller doses
  • Faster onset of action for respiratory medications
  • Smaller particle size of drug results in easier delivery into the lungs

Parenteral Route

  • Quicker onset of action systemically
  • Intravenous (IV) is route of preference for systemically acting drugs in emergency conditions (ex: fluids, cardiac medications, vasopressors, etc.)
  • More systemic side effects
  • Intramuscular (IM) and Subcutaneous (SQ) routes are slower to absorb and distribute resulting in greater onset of action time

IV Delivery

In certain cases, giving drugs through an IV may be considered a bolus injection (emergencies, pain management, anesthesia induction, etc.). Once the concentrated dose is pushed, it's followed by a flush of saline to ensure complete medication delivery.

Intraosseous (IO)

  • Administration of medications directly into the marrow of large bones
  • Only used when IV access cannot be established, or other routes are not available
  • Concerns: necrosis, infection, osteomyelitis

Down the Endotracheal Tube

In an emergency, specific medications can be delivered down the endotracheal tube (ETT) if IV/IO access is unavailable.

NAVEL:

| Letter | Medication | |--------|-----------| | N | Naloxone (Narcan) | | A | Atropine | | V | Vasopressin | | E | Epinephrine | | L | Lidocaine |

2–2.5 times the normal IV dose followed by 10mL saline flush.

Pharmacokinetics

Pharmacokinetics — actions the body performs with the drug.

ADME:

  • A — Absorption
  • D — Distribution
  • M — Metabolism
  • E — Elimination

Pharmacodynamics

Pharmacodynamics — mechanisms by which medications produce effects in the body.

  • Agonistic medications — stimulate receptors
  • Antagonistic medications — block receptors

Lock and Key Theory

Definition: How drugs, hormones, chemical substances and neurotransmitters can exert/act upon specific receptor sites.

  • The neurotransmitter is the "key" that holds the message
  • The receptor is the "lock" that will receive the message

Sympathetic Nervous System — Adrenergic Pathway

The Adrenergic Pathway falls under the sympathetic nervous system.

  • Adrenergic — stimulate receptors responding to norepinephrine/epinephrine
  • Anti-adrenergic — block receptors from responding to norepinephrine/epinephrine

Alpha(1) Receptors

Located in heart, lungs, and vasculature.

When stimulated, they will cause:

  • Vasoconstriction (increasing blood pressure)
  • An increased HR

Example: Vasopressors

Alpha Anti-Adrenergic Medications

  • Reduce arteriolar resistance
  • Produces vasodilation (lowers BP)

Example: These types of drugs are referred to as your "zosin" drugs — Prazosin, doxazosin, terazosin. Helps with blood pressure.

Beta 1 Receptors

Located in heart and kidneys.

When stimulated = will cause constriction/contraction THUS:

  • Increasing HR
  • Increasing myocardial contractility

Example: Dobutamine (increases HR & contractility)

Beta 2 Receptors

Located in lungs, pancreas, liver, intestines, and arteriolar smooth muscle.

When stimulated = cause relaxation:

  • Vasodilation (decreased BP)
  • Bronchodilation (opening up the airways)

Example: Albuterol, levalbuterol

Beta Anti-Adrenergic Medications ("Beta Blockers")

Block the effects of epinephrine and norepinephrine.

Result:

  • Reduces HR and BP
  • Primary treatment for hypertension

Example: Your "lol" drugs — atenolol, metoprolol, labetolol

Parasympathetic Nervous System — Cholinergic Pathway

Under the PNS, we follow the Cholinergic Pathway. These receptors (receivers) under this pathway are our muscarinic receptors.

  • Cholinergic — stimulate receptors to respond to acetylcholine
  • Anti-cholinergic — block receptors from responding to acetylcholine

Muscarinic Receptors

Located in airways.

  • M1, M3 when stimulated = cause constriction of the airways
  • Anti-cholinergic medications — will block stimulation of M1 and M3. This will result in bronchodilation.

Tips and Tricks

  1. Where is my receptor located?
  2. What number? (Key: 1 & 3 contract; 2 relax!)
  3. Am I stimulating the receptor or blocking the receptor? (agonist or antagonist)

Example: B2 Adrenergic Medication

  • Location: lungs, smooth arteriolar muscles, liver, pancreas, "guts"
  • 2 = relaxation
  • Agonist / stimulating
  • Result: Relaxation of the lungs / bronchodilation