Test 1 - Lecture 2 Flashcards
What are the “big three” ideal properties of a drug?
- Effectiveness - How well does it work?
- Safety - Remember there is no safe drug!
- Selectivity - The more selective the drug the better because it causes less side effects by hitting the right receptor. The size of the drug molecule, the shape of the molecule and the charge of the molecule effect the selectivity.
What is the therapeutic objective of a drug?
To provide the maximum benefit with minimal harm.
Why is it important for most drugs to be lipophilic as opposed to hydrophilic?
In order for a drug to directly penetrate a cell membrane it must be soluble in lipids.
Side Note: The smaller the molecule the better.
Where are drugs that are taken PO absorbed?
In the stomach and GI tract.
Pharmacotherapeutics
Defined as the achievement of the desired therapeutic goal from drug therapy - the desired outcome. It is the clinical purpose - the indication- for giving a drug.
Off label use
After a drug is approved, it is legally prescribed for a use that is not indicated on the label if the prescriber believes it to be of benefit.
T or F
Nurses are responsible for understanding the pharmcotherapeutics of all drugs that they administer.
True
Pharmacokinetics
The movement of the drug particles inside the body and the processes that occur during this movement.
pharmacon - drug or poison
kinesis - motion
What are the 4 phases of Pharmacokinetics?
- Absorption
- Distribution
- Metabolism (biotransformation)
- Excretion (elimination)
How does ionization effect drug effectiveness?
The charge of a drug molecule effects how easily it can go through cell membranes and bind to receptors.
Note:
1. Most drugs have no charge (non-polar).
2. Non-polar molecules are lipophilic.
T or F
Polar drug molecules are able to penetrate cell membranes.
FALSE Polar (charged) molecules are hydrophilic and CANNOT penetrate cell membranes.
What is the basic principal of a drugs action?
To modify existing functions within the body.
“No drug can be taken to grow a tail.”
Affinity
The attraction of the drug to the receptor - think of a magnet.
High affinity
Drug molecules bind to receptors at low drug concentration so a smaller dose is appropriate.
Low affinity
Drug molecules bind to receptors at a high drug concentration so a larger dose is appropriate.
Selectivity
The size, shape and charge of a molecule that determines whether it will bind to a receptor.
Absorption
The movement of a drug from route of administration into the bloodstream.
Note:
IV administration goes directly to blood and skips absorption.
Distribution
The movement of a drug through the bloodstream, into the tissues and eventually into the cells.
Metabolism (Biotransformation)
Transforming medicine from one substance to another.
This usually occurs in the liver but also occurs in the GI, kidney, lungs, brain and skin.
Usually goes from lipophilic to hydrophilic - The ability of a drug to become soluble in water is important because it allows the drug to be excreted through the renal system.
Excretion
Removes what the drug has become (metabolized into) and eliminates it from the body.
This occurs in the kidney.
Ion Trapping - also called pH portioning
When the pH on either side of a membrane differs, drug molecules tend to move to the side where ionization will occur. Once the molecules become ionized (charged - hydrophilic) they cannot move back through the membrane. Altering the pH on one side of the membrane alters the movement of the drug molecule.
An example is when the pH of urine is altered to pull an aspirin overdose out of the body.
Bioavailability
The fraction of a drug that is absorbed into the circulation after administration.
A bioavailability of 1 means that all of the given drug is available in the bloodstream. (scale is 0 to 1).
100% of a drug is absorbed
when given IV - bioavailability = 1.
Factors that effect absorption
Bioavailability Solubility - (lipophilic) Surface Area - more SA = Greater absorption Ionization = 0 charge Blood flow - If circulation is compromised it is decreased GI motility Age Other medications
What drug route takes the longest to be absorbed?
PO -
They need to be broken down before they can enter the bloodstream.
The presence of other drugs or food may also impair the rate of oral drug absorption.
What drug route is instantly absorbed?
IV - they are placed directly into the bloodstream.
T or F
Drugs given parenterally are absorbed quicker than drugs given orally.
True
They are already dissolved in a liquid form and therefore are absorbed more rapidly.
Factors that effect Drug Distribution
- Blood flow to the tissues.
- Drugs ability to leave the blood.
- Drugs ability to enter the cell.
- ** The larger the drug molecule the harder it is to leave the blood or cross the cell membrane.
- Protein Binding
- Blood brain barrier
- Placental membrane
What happens when a drug is bound to a protein?
It’s unable to pass through the capillary walls. It impedes a drugs ability to reach sites of action, metabolism or excretion.
T or F
Once a drug is bound to a protein it stays there forever.
False
The bond dissolves in time and the drug molecules will become free and active again.
How are drug dosages calculated?
By the drug manufacturer based on the protein binding characteristics of the drug.
How does malnutrition, liver failure, or severe burns effect distribution of a drug?
The distribution of the drug is altered due to the lack of protein. When less drug is bound to protein, more drug is free and can be distributed to the site of action, thereby causing increased therapeutic (possibly toxic), and possibly increased adverse, effects.
What types of drug molecules are capable of moving to their site of action and achieving the desired therapeutic effect?
Unattached free molecules. The free drug is active as opposed to the protein bound drug.
Blood brain barrier
The purpose of the blood brain barrier it is to keep toxins and poisons from reaching the brain. Instead of wide spaces between the cells and the capillary walls the cells are packed tightly together. The tight junction is hard to penetrate so treating meningitis or other infections of the brain is a challenge.
***Neonates/Newborns are not as tight yet so have to be careful with them too.
Placental membranes
Any drug that can pass through a membrane can pass through the placenta. To pass through, a drug must be lipophilic, not ionized, and not protein bound.
Everything Mom takes goes right to the fetus so need to exercise caution. Never give an X drug.
Does a high protein binding or low protein binding drug last longer in the bloodstream?
A high protein binding drug lasts in bloodstream longer.
Why are tube fed patients a concern when it comes to drug distribution?
They have more protein in their system which decreases the amount of active drug.
What will be the result of administering a high-protein bound drug to a patient with liver failure?
The drug will reach the target cells more quickly, which could result in a toxic effect.
Metabolite
A product of metabolism. Drugs that are metabolized are generally changed into an inactive form having no effect on the body as they travel throughout the body waiting to be excreted.
Prodrugs
Drugs that are inactive until metabolized into an active therapeutic form. Example: Primidone metabolizes into phenobarbital a strong anti-convulsant.
