01- Drug Administration and Absorption Flashcards
What are the topical routes of administration?
- Skin
- Inhalers
- Eye and ear drops
What does the term enteral mean?
Using/involving the gut to get the drug where it needs to go
What are the enteral routes of administration?
- Oral
- Rectal
What does the term parenteral mean?
Achieving the effect beyond the site of administration, used in highly vascularized areas
What are the parenteral routes of administration? 6
- Intravenous
- Subcutaneous
- Intramuscular
- Transdermal
- Intrathecal
- Sublingual
Which route is the most complex, and why?
Oral, the drug must break down, pass the hepatic portal system, enter the systemic circulation to produce biological effect
How does a bad liver affect absorption?
Decreases the first pass effect and increases risk for overdose
What type of administration would a cream on a rash would be considered?
Topical
What type of administration would administering the drug directly into the bloodstream be considered?
Intravenous
What type of administration would be administering drug under the skin be considered?
Subcutaneous
What type of administration would a vaccine be considered?
Intramuscular
What type of administration would a patch be?
Transdermal
What type of administration would be an epidural be considered?
Intrathecal
Which type of administration bypasses the first pass effect?
Parenteral route
What is drug absorption defined as?
The movement of a drug from its site of administration across body membranes, and into circulating fluids (bloodstream)
Which route of administration is the most direct?
Intravenous, goes right into the bloodstream, no first pass, and no drug lost!
Why (when using routes other than parenteral routes) do we need to increase the amount of drug given then what is needed to produce a biological effect?
Given more drug than what is needed because we assume that some drug will be lost with the first pass effect
What is the issue with giving the patient more drug due to the first pass effect?
If a patient has issues with organs associated with absorption/excretion then there is an increased risk of overdose
What are the factors affecting drug absorption?
- Route of administration
- Drug properties and formulation
- Drug dosage
- Blood flow at the administration site
- Digestive motility
- Digestive tract enzymes
- Intestinal P-Glycoproteins
What are some of the issues associated with drug properties and formulation?
- Drug in liquid form absorbed faster than drug in tablet form
- Some are slow/quick release
- Bind tight/loose
- H20/fat soluble
How does drug dosage influence drug absorption?
Increased concentration gradient causes the drug to move faster
How does blood flow at the administration site influence drug absorption?
No blood flow = no absorption
How do digestive tract enzymes influence drug absorption?
Some drugs do not tolerate stomach pH or enzymes
How do intestinal P-Glycoproteins influence drug absorption?
Bind to products as they try to cross membranes, trap them in the gut. Sometimes they get one more pass and will be absorbed, others trapped in the gut and eliminated with feces
What does the term excipient mean?
This is what the bulk of the drug is called, makes it large enough for us to hold and consume
What must happen to the drug before it can be absorbed?
Must first dissolve from its excipient in the stomach or the intestines which are largely composed of water. To enter circulation drugs must pass through lipid rich plasma membranes
What is the issue with the drug dissolving and absorbing?
Drugs want to be H20 soluble to dissolve, but they also want to be lipid soluble in order to absorb
What must fat soluble drugs be taken with?
Food, changes stomach contents and allows it to dissolve from excipient
If a drug is highly water soluble, which route can the drug be administered by?
The intravenous route (will dissolve into the blood)
What type of drug cannot be administered IV?
Fat soluble drugs
Oral administration has a ________ onset of action
slower
IV administration has a _________ onset of action
quicker
What is the purpose of the excipient?
- Adds bulk to the tablet
- Enhances the rate of dissolution
- Slows the rate of dissolution
Which processes allow for absorption of drugs?
- Passive diffusion
- Carrier mediated transport
What are the characteristics of drugs that can be absorbed via passive diffusion?
- Small in molecular size
- Non-polar (lipid soluble)
How do drugs move via passive diffusion?
With the concentration gradient
What are the characteristics of drugs that can be absorbed via carrier mediated transport?
- Large in molecular size
- Polar (water soluble)
How do drugs move via carrier mediated transport?
- Actively transported across biological membranes
- Often requires energy
- Can’t push the system harder than its prepared to move
What are the characteristics of the stomach?
- Distensible
- Well vascularized
- Highly acidic (pH=2)
- Powerful hydrolytic enzymes
- Dwell time controlled by digestive processes
What are the characteristics of the small intestines?
- Well vascularized
- Greater surface area than stomach
- Highly basic (ph=8)
- Dwell time controlled by digestive processes
What happens when you put a weak acid into a water filled space?
Will give away its proton (when the environment is acidic), leaves it non-ionized and fat soluble
Weak acids are absorbed in what kind of environment?
Acidic environment (ex. stomach)
ASA is absorbed better on what kind of stomach?
Empty stomach, keeps the pH low
What happens to weakly acidic drugs in acidic environments?
Weakly acidic drug remains in its non-polar form
Does the stomach have few protons or many protons?
Many protons
Do the small intestines have few protons or many protons?
Few protons
Does the stomach favour the charged or uncharged form?
Uncharged
Do the small intestines favour the charged or uncharged form?
Charged
What happens to weakly acidic drugs in basic environments?
Drug becomes polar
What type of drug is absorbed better in the intestines?
Weakly basic
What type of drug is absorbed better in the stomach?
Weakly acidic
What happens to weakly basic drugs in basic environments?
Weakly basic drug remains in its non-polar form
What happens to weakly basic drugs in acidic environments?
Weakly basic drug becomes polar
What is our physiological pH?
Around 7.4
Stomach vs Intestines
We have acidic and basic compartments. Around 80% will remain in neutral form to be absorbed. f the drug remains H20 soluble it is trapped. Move across lipid membranes if lipid soluble 80% of charged stays, 20% fat soluble, moves to tissue, 20 changes and so on
