Gord Patterson, ALS-CCT, ACP
The ABC’s Of Drugs

Pharmacodynamics
 Study of the mechanisms by which drugs act to
produce biochemical or physiological changes in
the body

Pharmacokinetics
 Study of how drugs enter the body, reach their
site of action and are eliminated from the body
Pharmacokinetics
 Study
of how drugs enter the body,
reach their site of action and are
eliminated from the body
Physiology Review

Paramedic therapeutic best practice is
achieved through a knowledge of
physiology, biology and chemistry.

Understanding concepts of drug
duration effects, accumulation, action,
and metabolism is key to responsible
paramedicine.
Understanding cell membranes is
essential to pharmacokinetics
Plasma membranes
Dual Lipid layer membrane
 Cell membranes charges create gradients
on either side of the membrane
 Non polar Lipid tails
○ Hydrophobicity
 Repels water –
 Polar Lipid heads
○ Hydrophilicityn
 Attracts water –
Transport Mechanisms
 Moving
from between body
compartments against concentration
gradients
 Passive Transport - zero energy required
 Active Transport - Requires energy
Passive Transport

Diffusion – high concentration to low
concentration –
 Simple diffusion
Osmosis – Solvent (H20) moving from
high concentration to low concentration
 Filtration – molecules moving across
membrane from higher pressure to
lower pressure

Active transport
& K – ATP pump pushes against a
gradient
 Na
Carrier mediated diffusion
 Facilitated diffusion (some references
consider passive. Our book states
active)

Acid- Base Chemistry

Acid is a pH < 7.0 and will give up a proton
Base is a pH > 7.0 and will accept a proton

Blood pH is 7.35 – 7.45

pH of environment may determine how a drug
charge will exist – protonated or deprontonated ionized
Concept of ionized versus non-ionized may
determine the rate at which a drug is absorbed in
hydrophobic lipid non polar center. Non ionized can
pass through lipid membrane centers easily but
water and polar drugs cannot.


Hydrophobic cellular membrane’s interior
prevents polar drugs, ions and large non polar
substances from crossing

Concept of ionized versus non-ionized
may determine the rate at which a drug
is absorbed in hydrophobic lipid non
polar center. Non ionized can pass
through lipid membrane centers easily
but water and polar drugs cannot.
Carrier mediated transport

There are two forms of carrier-mediated
transport, active transport and facilitated
diffusion. The rapid transfer of drug
metabolites into urine is by active transport.
Entry of glucose into most cells is by facilitated
diffusion but its passage across the
gastrointestinal mucosa is by active transport.
Active transport requires a direct expenditure
of energy, whereas facilitated diffusion is not
energy dependent. Active transport can move
substances against a concentration gradient,
facilitated diffusion cannot.
Osmosis
Facilitated diffusion
Active Transport
Carrier mediated diffusion
Five phases of Pharmacokinetics
Liberation
 Absorption
 Distribution
 Metabolism
 Elimination

Rx Liberation
Liberation only applies to oral
medications.
 The process by which a drug is released
from its delivery device during digestion

 Tablet, capsule, etc

The rate of liberation is determined by
it’s composition
 Powder versus tablet
Factors affecting Rx absorption
pH of the Rx
 Surface area of the Rx area

 Ie: powered Rx provides more surface area
for transference than the outer surface of a
tablet.
Surface area of the absorbing
environment
 Rate of blood flow

 Hypothermia
 Shock
Factors affecting Rx absorption
Rx concentration
 Design of the Rx
 Delivery route

Factors affecting Rx distribution
Protein binding
 Perfusion status
 Vascular supply to the target tissue
 Blood pH
 Presence of other serum binding drugs
 CNS blood brain barriers
 Placental barrier
 Competing tissues

Biotransformation

Metabolism or breaking down of Rx’s
 May only transform Rx to less active
metabolite
 Change the physical properties i.e.: to
become fat soluble
May “Pordrug” to active targeting Rx
 Liver is a main player here

Special considerations
Route dependant First Pass – Liver
changing undesirable metabolite
prevention
 Hydrolysis – making water soluble
 Oxidation – oxygenation Rx breakdown
to ease elimination
 Rx Metabolism - The chemical processes

changing the Rx into metabolites
Drug Elimination

Kidneys - urine
 Glomerular filtration
 Tubular secretion
Bile
 Expired air
 Sweat
 Tears
 Feces

Pharmacodynamics

Study of the mechanisms by which drugs act to
produce biochemical or physiological changes in
the body
Consider Captopril
What drugs can do
Interact with specific receptor proteins in
and on cells
 Receptors exist to respond to the
stimulus of endogenous
neurotransmitters
 Drugs can either mimic the effect of
regulatory molecules or block them
 Drugs can only increase or decrease the
rate at which a given physiologic
process works

At a Glance

Drugs can increase or decrease the rate
at which a process works

Drugs cannot make the body do
something it couldn’t do otherwise
Define the terms:
Affinity
 Efficacy
 Agonist
 Antagonist
 Competitive
 Antagonism
 Second messenger
 Down-regulation

Define the terms:









Up-regulation
Agonist-antagonist
Non-competitive antagonism
Irreversible antagonism
Side effect
Iatrogenic response
Tachyphylaxis
Synergism
Potentiation
Define the terms:
Summation
 Biological half-life
 Drug interaction
