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• Medication distribution in the body is determined by the chemical and physical properties of the medication, as well as patient-specific factors.

Barriers to Medication Distribution

• The body has natural barriers to prevent foreign substances from entering.
• Medication molecules must navigate these barriers through:
  • Osmosis: Enhances distribution by allowing IV fluids to leave the intravascular space and enter tissues/cells.
  • Filtration: Redistributes water and particles via hydrostatic pressure across semi-permeable membranes.
• Epithelial cells in the skin, GI tract, eyes, and urinary tract form continuous barriers.
• Small, non-ionized, and lipophilic medication molecules pass through cell membranes easily.
• Larger, hydrophilic, and ionic medication molecules require active transport or facilitated diffusion.
• Three key barriers hinder medication from reaching tissues: the blood-brain barrier, blood-placenta barrier, and blood-testes barrier.
• Molecules pass freely through capillaries in the kidney, thyroid, pancreas, lungs, and peritoneum.

Plasma Protein Binding

• Medication molecules temporarily attach to proteins in blood plasma.
• Changes in plasma protein levels or introduction of other protein-binding medications can alter medication concentration.
• Plasma protein binding increases the amount of medication needed for clinical effect.
• The medication is released as circulating levels fall, leading to a longer duration of action.

Lipophilic Medications and Fat Tissue

• Fat tissue can alter the amount of medication available for action.
• Lipophilic medications can be sequestered in the fat tissues of obese individuals, causing slow release and prolonged effects.

Volume of Distribution

• It describes the extent of medication spread within the body.
• Some medications stay primarily in the plasma, while others spread into water throughout the body.
• Some medications bind with bone, teeth, or other tissues.
• Medications with a lower volume of distribution have higher plasma levels compared to those with a higher volume of distribution.

Medication Metabolism (Biotransformation)

• Biotransformation is a chemical change that medications undergo in the body.
• A medication can become an active metabolite (capable of pharmacologic activity) or an inactive metabolite (lacking the ability to alter cell processes).
• Biotransformation can have four possible effects:
  • An inactive substance becomes active.
  • An active medication is changed into another active medication.
  • An active medication is completely or partially inactivated.
  • An active medication is transformed into a substance easier for the body to eliminate.
• Most biotransformation occurs in the liver via the cytochrome P450 system.
• The P450 system's enzyme pathways can be influenced by other medications, chemicals, and diet.
• The kidneys, skin, lungs, GI tract, and other body tissues also have some biotransformation capabilities.
• Biotransformation makes medications and chemicals more water-soluble for easier elimination.
• Suspect altered metabolism in patients with chronic alcoholism, liver disease, or any liver-affecting condition.

Medication Elimination

• The primary route of medication removal is through the kidneys.
• Factors influencing elimination rate:
  • Kidney disease or dysfunction.
  • Acute or chronic renal failure.
  • Renal blood flow.
  • Urinary tract obstruction.
  • Alterations in urine pH.
• Two patterns of metabolism and elimination:
  • Zero-order elimination is when a fixed amount of substance is removed during a period regardless of the total amount in the body.
  • First-order elimination is when then the rate of elimination is directly influenced by the plasma levels of the substance (more substance = more elimination).

Half-Life

• Half-life is the time needed for metabolism or elimination of 50% of the substance in the plasma.
• It is altered by disease states, changes in perfusion, and medication interactions.
• Half-life refers to the quantity of medication in the body, not the clinical effects.
• Medications are administered at a dose and frequency that equals the body's rate of elimination to maintain a constant level.
• Smaller amounts of medications can be eliminated through lungs, stools, saliva, breast milk, and perspiration.

Reducing Medication Errors

• Medication decisions are often based on memory and made in stressful situations.
• Strategies to reduce errors:
  • Perform a verbal readback of orders received from online medical control.
  • Call out the medication name and dose prior to administration.
  • Label unlabeled syringes to prevent confusion.
  • Build an environment in EMS where providers feel comfortable reporting errors.
  • Bring a patient's home medications if they are new to the area or on new medications from a specialist.
  • Use a reliable reference source when administering unfamiliar medications or doses.
  • Confirm the volume in a syringe or weight-based medication calculation with a partner.
  • Evaluate the patient for medication allergies or hypersensitivity before each administration
• The Institute for Safe Medication Practices (ISMP) has a list of error-prone medication abbreviations.

The Rights of Medication Administration

• The initial five rights:
  • Right patient.
  • Right medication.
  • Right dose.
  • Right route.
  • Right time.
• Expanded rights:
  • Right patient education.
  • Patient's right to refuse.
  • Right response and evaluation.
  • Right documentation and reporting.

Drugs Acting on the Sympathetic Nervous System

• Receptor sites are proteins connected to cells throughout the body, activated by chemicals.
• Drugs influencing the sympathetic nervous system are classified by the receptors they interact with.
• Alpha 1 receptors: effect small arteries and arterioles
• Alpha 2 receptors: effect pancreatic enzyme and insulin release
• Beta 1 receptors: One heart
• Beta 2 receptors: Two lungs
• Beta 3 receptors: effect heat production and fat
• Nicotinic receptors
• Opioid receptors

Sympathetic Nervous System Receptors

• Receptors are labeled as alpha or beta.
• Beta agents increase heart rate, force, and automaticity.
• Arteries have both alpha and beta receptors:
  • Alpha drugs cause vasoconstriction.
  • Beta drugs cause vasodilation.
• Lungs also have alpha and beta receptors:
  • Alpha agonists cause vasoconstriction.
  • Beta agonists trigger bronchodilation.
  • Beta 1 - One heart
  • Beta 2 Two Lungs
  • Arteries have both alpha and beta receptors.
• Beta-sympathomimetic agents can be classified into beta-1 and beta-2 groups.
• Sympatholytic or sympathetic blockers block the action of sympathetic agents.
• Types of Alpha and beta:
  • Phenylephrine
  • Norepinephrine
  • Epinephrine
  • Isoproterenol

Beta Blockers vs Beta Stimulators

• Beta Blockers say "I got here first I'm telling the heart not to beat so fast"
• Beta Stimulators say "I was supposed to go here"

Beta-Adrenergic Blockers:

• Occupy receptors in the heart, lungs, arteries, and elsewhere.
• Indications are based on properties of the drugs and interaction with the autonomic nervous system.
• Examples:
  • Atropine (parasympathetic blocker).
  • Norepinephrine (sympathetic agent, primarily alpha).
  • Isoproterenol (sympathetic agent, almost pure beta).
  • Epinephrine (sympathetic agent, predominantly beta).
  • Dopamine (sympathetic agent).
  • Albuterol (sympathetic beta-2 agent).
  • Propranolol (sympathetic beta-blocker).