Principle of Pharmacology - pharmacokinetics Flashcards
(39 cards)
Pharmacokinetics
How the body affects the drug
Pharmacodynamics
How the drug affects the body
Excipients
Everything except the drug itself (colouring, flavourings, sweeteners)
First Pass Effect
Rapid uptake and metabolism of compound in LIVER before it reaches systemic circulation
Idea of first pass effect
So the idea of the first pass effect is that when you take a compound it goes to your liver to be metabolized. This means that the drug concentration will drop therefore once it is done in the liver it can reach its target area but with a lower dose. Lower dose of absorption = decrease in effect
What happens when you have a patient come in with liver damage?
When the drugs reach the damaged liver it will not be broken down as efficiently if it were a person with a normal liver. This means that the drug percentage released to the rest of the body will be greater than someone with a liver that works properly. This can lead to serious consequences –> overdose…
Drugs are given as a
Formulation
Examples of formulations
tablets
capsules (powder in gelatin coating - fast absorption)
caplets (easily swallowed)
liquids (fastest absorption)
What makes a drug cheap?
When it doesn’t have to be sterile - PO or SL formulations
Bioavailability and use insulin as an example
Fraction of drug available in systemic circulation
PO: lower than if you were given IV
Insulin: if given PO enzymes in stomach would break it down before getting into circulation. Injected is the best way to go!
What does SL, SC, IM, and IV administration all have in common?
High bioavailability
By passes stomach and intestine
NO first pass (doesn’t go to liver)
Name the three enteral methods for drugs to be administered
- PO (orally)
- PR (rectal)
- SL (sublingual)
Name the five parenteral methods for drugs to be administered
- IV
- IM
- SC
- Transdermal
- Inhalation
Why would we use the enteral route for a drug?
- Convenient
- Negative: first pass effect
Why would we use the parenteral route for a drug?
- No first pass effect
- Quick to get into circulation
- More drug reaches circulation
Why would we use the topical route for a drug?
Local/sustained effect
Most drugs use (active OR passive) movement across the membrane
Passive!
Why? Because it goes down the concentration gradient when moving across the membrane.
3 chemical factors that affect the way a drug is absorbed
- Size
- Lipid solubility - lipid soluble drugs will absorb more quickly because they pass readily through membranes (water soluble drugs will pass more slowly) * phospholipid bi-layer of cells acts as a barrier to large water-loving molecules
- Drug charge - development of an electric charge decreases drugs ability to move around body
4 physical factors that affect the way a drug is absorbed
- Blood flow to the site of absorption
- Surface area for absorption - high surface area in intestine
- Contact time - if you have diarrhea then the drug will have decreased contact time compared to if you did not have it
- Drug formulation - size, gel coatings…
Which administration would we NOT use if a person is in shock?
Subcutaneous because blood flow to the extremities is greatly reduced
The distribution of a drug depends on…
rate of blood flow
Why will the tissues with high blood flow receive more drug than tissues that have low blood flow to them? Examples of rapid distribution and slow distribution.
Tissues with high blood flow will receive more drug because it will get to its destination faster and more frequently than a place with low blood flow
- heart, liver, kidney, brain
- muscle, fat, skin (all dense)
Drug distribution is determined by three factors
- Rate of blood flow to tissues
- Exiting vascular system
- entering cells to target goal
When a drug exits the vascular system what are the factors that affect it?
- lean mass (watery environment will allow drug to be absorbed more quickly)
- Fat solubility
- Plasma Protein Binding*
