Module 2 Flashcards
Define pharmacodynamics
The study of the biochemical and physiologic effects of drugs (what drugs do to the body and how they do it)
What does pharmacodynamics include?
- Dose-response relationships
- Drug-receptor interactions and drug responses that do not involve receptors
- Interpatient variability in drug responses
- the therapeutic index
What is dose-response relationships?
The relationship between the size of an administered dose and the intensity of the response produced
What does the dose response determine?
- The minimum amount of drug to be used
- The maximum response a drug can elicit
- How much to increase the dosage to produce the desired increase in response
As the dosage increases, what happens to the response?
It becomes larger
How is treatment adjusted regarding dose-response relationships?
Adjusted by increasing or decreasing the dosage until the desired intensity of response is achieved
What three phases occur in dose-response relationships?
Phase 1: occurs at low doses
Phase 2: an increase in the dose elicits a corresponding increase in the response
Phase 3: when the curve flattens and a point is reached at which an increase in dose is unable to elicit a further response
What two properties of drugs are revealed in dose-response curves?
Maximal efficacy
Relative potency
What is maximal efficacy?
The larges effect that a drug can produce
What is relative potency?
The amount of drug that must be given to produce an effect
(Implies nothing about maximal efficacy)
Define drugs
Chemicals that produce effects by interacting with other chemicals
Define receptor
Functional macromolecule in a cell to which a drug binds to produce its effects
What are we typically referring to when using the term “receptor”?
The body’s own receptors for hormones, neurotransmitters, and other regulatory molecules
Is the binding of a drug to its receptor reversible?
Usually
What happens when a drug binds to a receptor?
It will mimic or block the action of the endogenous regulatory molecules
And increase or decrease the rate of physiologic activity normally controlled by the receptor
What does it mean that drugs can only mimic or block the body’s own regulatory molecules?
Drugs cannot give cells new functions
(Drugs cannot make the body do anything it’s not already capable of doing. They can only alter the rate of pre-existing processes)
What are the four primary receptor families?
Cell membrane
Ligand-gated ion channels
G protein
Transcription factors
How does the cell membrane receptor family work?
Embedded enzymes, on the surface of the cell
How does the ligand-gated ion channels receptor family work?
Regulate the flow of ions into and out of the cells
How does the G protein-coupled receptor systems receptor family work?
With the receptor
How does the transcription factors receptor family work?
Intracellularly
What occurs if a drug is more selective?
Fewer side effects
How do receptors make selectivity possible?
By the existence of many types of receptors.
Each type of receptor participates in the regulation of just a few processes
Why does the lock and key mechanism of receptors not guarantee safety?
- The receptor can still produce non-selective results if it is responsible for regulating several processes
- Drugs that interact with it will also influence several processes
The body has receptors for each type of?
Neurotransmitter
Hormone
What are agonists?
Molecules that activate receptors
What qualities do agonists have?
Affinity
High intrinsic activity
What do agonists do?
**Can make processes go “faster” or “slower”
What are endogenous regulators considered?
Agonists
What do antagonists do?
At the receptor site, they prevent some kind of action from occuring
How do antagonists work?
By preventing receptor activation by endogenous regulatory molecules and drugs
Do not cause receptor activation but cause pharmacologic effects *by preventing the activation of receptors by agonists
Qualities of antagonists
Affinity
No intrinsic activity
In which ways can receptors build sensitivity?
The number of receptors on the cell surface
The sensitivity to agonists can change
How can the number of receptors on the cell surface and the sensitivity to agonists change?
In response to:
Continuous activation (making things happen)
Continuous inhibition (stopping things from happening)
What happens with continuous exposure to an agonist?
Desensitized or refractory
Or undergo downregulation
What happens with continuous exposure to an antagonist?
Becomes hypersensitive, or supersensitive
Examples of drugs that do not work by using receptors:
Antacids
Antiseptics
Saline laxatives
Chelating agents
What does interpatient variability in drug responses mean?
The dose required to produce a therapeutic response can vary among patients
How is the measurement of interpatient variablity found?
Through a formula called ED50
What is the ED50?
Formula that finds the dose required to produce a therapeutic effect in 50% of the population
What is the therapeutic index?
Measure of a drug’s safety
How is a drug’s therapeutic index found?
Ratio of the drug’s LD50 (average lethal dose to 50% of the animals treated) to its ED50
What does a high therapeutic index mean, vs. a low therapeutic index?
*The larger/higher the therapeutic index, the safer the drug
*The smaller/lower the therapeutic index, the less safe the drug is
What are drug-drug interactions?
Interactions that occur when a patient is taking more than one drug. Some are intended and some are not
What are the consequences of drug-drug interactions?
Intensification of effects:
- increased therapeutic effects
- increased adverse effects
Reduction of effects: (block each other out)
- decreased therapeutic effects
- decreased adverse effects
Or creation of a unique response
Example of drug-drug interaction that increases the therapeutic effects
Ampicillin and sulbactam (antibiotics)
Example of drugs-drug interaction the increases adverse effects
Aspirin and warfarin (both thin the blood)
Example of drug-drug interaction that decreases therapeutic effects
Propranolol and albuterol (propranolol is a beta blocker and albuterol blocks receptors in the lung)
Example of drug-drug interaction that decreases adverse effects
Narcan and morphine (narcan blocks receptors from morphine to prevent adverse effects from it)
Example of drug-drug interaction resulting in a unique response
Alcohol with Antabuse/disulfiram (makes you really sick)
Four basic mechanisms of drug-drug interactions:
- Direct chemical or physical interaction
- Pharmacokinetic interaction
- Pharmacodynamic interaction
- Combined toxicity
Why should you never combine drugs in the same container without establishing compatibility?
They could have a direct chemical or physical interaction
What should you do if you’re unsure if drugs are compatible?
Need to call the pharmacy to make sure they’re compatible before mixing them together
What’s important to know about mixing intravenous solutions?
Chemical or physical interactions are most common in intravenous solution
If they cause precipitation - do not mix
Types of pharmacokinetic drug-drug interactions:
Altered absorption
Altered distribution
Altered renal excretion
Altered metabolism
Cytochrome P450 (CYP) group of enzymes
What can cause altered absorption in pharmacokinetic interactions?
Elevated gastric pH
Laxatives
Drugs that depress peristalsis
Drugs that induce vomiting
Adsorbent drugs
Drugs that reduce regional blood flow
What can cause altered distribution in pharmacokinetic interactions?
Competition for protein binding
Alteration of extra cellular pH
What can cause altered renal excretion in pharmacokinetic interactions?
Drugs can alter:
Filtration, reabsorption, active secretion
What can cause altered metabolism in pharmacokinetic interactions?
Most important and complex mechanism in which drugs interact,
The cytochrome P450 (CYP) group of enzymes can really impact a lot of medications, taking multiple meds together can affect this group
What is p-glycoprotein?
Transmembrane protein that transports a variety of drugs out of cells
What happens to the intestinal epithelium if there is recused or increased PGP?
Affects absorption
What happens to the placenta if there is reduced or increased PGP?
Affects drug export from placental cells to maternal blood
What happens to the blood-brain barrier if there is reduced or increased PGP?
Affects drug export from the cells of the brain capillaries into the blood
What happens to the liver if there is increased or decreased PGPs?
Affects drug export from liver into bile
What happens to kidney tubules when there is an increase or decrease of PGPs?
Affects drug export from renal tubular cells into the urine
What pharmacodynamic interactions occur if there is a drug-drug interaction at the same receptor?
Almost always inhibitory (antagonist/agonist)
(They constantly fight each other and we don’t get a response)
What pharmacodynamic interactions occur if there is a drug-drug interaction at separate receptor sites?
May be potentiative (work well together Ex: morphine and diazepam)
Or
Inhibitory (hydrochlorothiazide and spironolactone)
What is combined toxicity?
Drugs with overlapping toxicities should not be used together