Pharmacodynamics Flashcards
Pharmacodynamics
- Study of how a drug affects the body (Drug Action)
~ Physiological effect a drug has
Site of Action
- Molecular site where the drug has a significant chemical interaction, which causes a biological effect
~ Takes advantage of receptors
normally used for endogenous
chemicals - Site of Action
~ Surface of internal cell receptors
~ Internal cell enzymes
Receptor/Drug Interaction: Receptor
- Molecule within a cell, or on the cell
membrane - Relationship between the drug and
the receptor is similar to that of a lock
and key
~ Has to do with shape
> If receptors don’t fit with each
other, they don’t work - Each cell has receptors that are necessary to proper functioning of that specific cell
- Reaction to changes in chemical concentration
~ Increase or decrease the number of
receptors to adapt to the
environment
> Add more receptors when
chemical levels are low
> Decrease number of receptors
when chemical levels are high
~ Increase or decrease the sensitivity
of a receptor
> Increase sensitivity when
chemicals are low
> Decrease sensitivity when
chemical levels are high
Receptor/Drug Interaction: Effects of Binding
- The drug can directly cause changes
- The drugs can inhibit the binding of natural chemicals or another drug
Receptor/Drug Interaction: Affinity and Efficacy
- In order for a drug to trigger an effect it must have both affinity and efficacy for a receptor
- Affinity: chemical structure fits the receptor structure
- Efficacy: chemical causes a biological response when fit into the receptor
Drug Action Concepts: Additive Effect
Effect of taking two or more drugs is equal to the sum of the responses obtained when the drugs are taken individually
Drug Action Concepts: Synergistic Effect
Use of one drug enhances the effect of another
Drug Action Concepts: Antagonistic Effect
Use of is drug reduces the effect of another
Drug Action Concepts: Placebo Effect
Pt. anticipates a specific response and perceives that response despite taking a drug that has no therapeutic effect
Drug Action Concepts: Tolerance
- Diminished response to a drug as a result of continued use. Must take more of a drug to get the desired effects
~ Body produces more enzymes
responsible for metabolism
~ Cell reduces number of sensitivity of
receptors
Dose-Response Relationship
- As the amount of a drug is increased the effects increase since more receptor binding takes place
~ Drug/receptor interaction is by
chance so increasing the dose
increases the chance of interaction
~ When all receptors are occupied,
increasing dose has no effect
Dose-Response Relationship: Multiple Doses
- The levels of the drug increase and then level off when the amount of drug administered is equal to the amount of drug being eliminated
- Leveling off is known as steady state
Dose-Response Relationship: Maintenance Dose
Dose used to maintain steady state/therapeutic levels of a drug
Dose-Response Relationship: Loading Dose
- One or more doses that are higher than the maintenance dose
- Used to get to a therapeutic level quicker
Dosing Frequency Abbreviations
- q.d. - once a day
- quaque (each/every) die (day)
- q4h - every four hours
- qam - every morning
- qpm - every night
- b.i.d. - twice a day
- bis (twice) in die
- t.i.d. - three times a day
- ter (thrice) in die
- qi.d. - four times a day
- quater (four times) in die
Dose Calculations
- Standard doses for drugs are often variable to make sure the amount of drug needed to get the therapeutic effect is taken while allowing safety/effective elimination of the drug
~ Children
> 2-5
> 6-12
~ Adults
~ Elderly (reduced ability to metabolize/
excrete) - Most focus is on amount of drug relative to weight or body surface area
Why is dose modified for the elderly?
- Diminished blood flow to the liver and function of metabolizing enzymes found in the liver
- Reduced kidney function
Drug Interactions
- Addition of a drug increases or decreases the effect of another
~ Not always a negative factor; can be
used to a therapeutic advantage in
some situations
Drug Interactions: Receptor Antagonist
- Two drugs have affinity (fit) to a receptor
~ If one binds to the receptor, the other
can’t
Drug Interactions: Enzyme Induction
- One drug causes increased production of the enzymes that metabolize another drug
- Remember that the metabolites are usually inactive forms of the chemical, but can also be more active forms
~ Usually increases the inactive forms
so drug is less effective
Drug Interactions: Enzyme Inhibition
- One drug binds with the enzymes that metabolize another drug
- The effects of the second drug are stronger and longer lasting
Drug Interactions: Physiological Antagonism
- Physiological effect of one drug is opposite to the physiological effect of another drug
- Ex: one drug is taken to mange high blood pressure, but the person also has a cold
~ ACE inhibitor (vasodilator) vs. Nasal
decongestants (vasoconstrictor)
Drug Interactions: Physiological Agonists
- 2 drugs used at the same time have the same physiological effect, but the exact mechanism of action is different
- Ex: 2 drugs may decrease pain, but the way they do is different
~ Ibuprofen and Morphine
Drug Interactions: Absorption Effects
- Use of one drug affects the absorption of another
- Ex: taking a laxative while also taking antibiotics for infection
~ Portions of the laxative binds with the
antibiotic making absorption more
difficult
Drug Interactions: Excretion Effects
- One drug changes the excretion rate of another drug
- Ex: one drug occupies the excretion sites at the kidney blocking excretion of the other
Adverse Drug Reactions
- Undesirable response from a drug
~ Includes drug interactions when the
result is undesirable
Adverse Drug Reactions: Side Effects
- Expected adverse reactions based on the action of the drug
- Side effects experienced vary due to varied physiology of individuals
~ Person may experience a number of
side effects or none at all
Adverse Drug Reactions: Allergic Reactions
- Body reacts to a foreign chemical/inflammatory response
~ Majority from antibiotics and non
steroidal anti-inflammatory drugs
~ S&S
> Minor
• Itching
• Swelling
• Hives
> Major
• Bronchospasm (lack of O2 to
lungs)
• Anaphylactic Shock (lack of O2
to organs)
* Body goes through
inflammatory response
causing vasoconstriction
then vasodilation resulting
in low BP
Adverse Drug Reactions: Organ Cytotoxic Effects
- Drugs has adverse effect in organs especially those involved in metabolism and excretion of drugs
~ Liver
~ Kidneys
Adverse Drug Reactions: Idiosyncratic Reactions
- Reaction that is specific to a person or a specific group of people
~ Specific genetics cause people to
experience reactions not seen in the
general population
> Variations in receptors - more or
less sensitive/more or less in
number
> Variations in metabolizing
enzymes - more or less
breakdown of the drug
Adverse Drug Reactions: Drug-Food/Drug-Herbal Reactions
- Drug interacts with food in the diet
~ May increase drug action
> Antidepressants Vs. Aged Cheese/
Meats
~ May decrease drug action
> Blood thinners vs. Vitamin K foods
