Pharmacokinetics- Absorption Flashcards
Define Pharmacokinetics
How the human body acts on the drugs.
State the importance of Pharmacokinetic properties of a particular drug.
Hint: 6
To determine:
- Route of administration
- Dose
- Onset of action
- Peak action time
- Duration of action
- Frequency of dosing.
What is the AIM of drug therapy?
Prevent, cure or control various disease states.
What is Absorption?
The process of movement of unchanged drug from its site of administration to the systemic circulation.
State the major routes of administration.
Hint: PET IT
Parenteral
Enteral
Topical
Inhalational
Transdermal
Give 5 Advantages of Parenteral route - INTRAVASCULAR (IV)
HINT: Unconscious person
- 100% Bioavailability
- Fast absorption
- Low concentration of drug required.
- Suitable for unconscious patients.
- Bypass the liver
Give 5 Disadvantages of Parenteral route - INTRAVASCULAR (IV)
- Belonephobia - fear of needles and injection.
- Most dangerous routes of administration.
- Risk of infectious diseases (HIV) when needles are shared.
- Need for strict asepsis (absence of microorganisms).
- Painful and expensive
Give 3 Advantages of Parenteral route - INTRAMUSCULAR (IM)
Hint: Diabetic person
- No need for hospitalization.
- Patient can self administer.
- Suitable for water insoluble drugs.
Give 2 Disadvantages of Parenteral route - INTRAMUSCULAR (IM)
- Painful and has slower distribution.
2. Higher dose is needed due to slow onset of action.
Give 3 Advantages of Parenteral route - SUBCUTANEOUS
- Avoids harsh GI tract environment.
- Can be used for suspensions.
- Little training necessary.
Give 3 Disadvantages of Parenteral route - SUBCUTANEOUS
- Pain
- Tissue damage.
- Cannot be used for large volumes.
Give 4 Advantages of Enteral route - ORAL
- Can be self administered.
- Painless
- Economical
- Convenient
Give 4 Disadvantages of Enteral route - ORAL
- Slow absorption
- Slow action
- Irritation to gastric mucosa - nausea and vomiting.
- First-pass-effect (drugs are initially transported to the liver via the portal vein).
Give 4 Advantages of Enteral route - SUBLINGUAL
- Economical
- Quick drug absorption
- First-pass is avoided.
- Quick termination
Give 3 Disadvantages of Enteral route - SUBLINGUAL
- Unpleasant and bitter drugs.
- Large quantities are not given.
- Irritation of oral mucosa.
Give 3 Advantages of Enteral route - RECTAL
- Used to administer Anti-emetic agents (drugs effective against vomiting/unconscious).
- Higher concentrations rapidly achieved.
- Used in children.
Give 3 Disadvantages of Enteral route - RECTAL
- Embarrassing
- Inconvenient
- Absorption is slow and erratic.
For absorption, a drug needs…..
To cross the cell membrane.
What is Passive diffusion?
Major process for absorption
Process by which drug molecules diffuse from region of higher conc. to region of lower conc.
What is Filtration / Pore transport?
The passage of drugs through aqueous pores in the membrane or through paracellular space.
What is the driving force for Passive diffusion?
The concentration of electrochemical gradient.
State the driving force for Filtration / Pore transport.
Hydrostatic pressure or osmotic differences.
Importance of Filtration / Pore transport is…
Absorption of low molecular weight, low molecular size and chainlike linear compounds.
What is Carrier Mediated transport?
Process by which drug molecules bind to transporters / carriers and then is translocated across the membrane and released on the other side.
Define Facilitated diffusion.
The movement of substrate of a single class (uniporters) down a concentration gradient.
Name some substances that use Facilitated diffusion.
Hint: GAP
G: glucose
A: amino acids
P: peptides
Name some substances that use Filtration / Pore transport.
Hint: Upolu Western Samoa
Upolu: urea
Western: water
Samoa: sugar
Define Active transport
The movement of molecules from a low conc. to a high conc.
Difference between Facilitated diffusion and Active transport?
Facilitated diffusion = no energy is expended
Active transport = energy is needed
What is Primary active transport?
Transport that directly uses a source of chemical energy (e.g., ATP)
What is Secondary active transport?
Transport that has no direct energy requirement.
Define Symport (co-transport)
Transport of both molecules in the same direction.
Define Antiport (counter-transport)
Movement of molecules in opposite direction.
What is Transcellular / Intracellular transport? Give an example.
The passage across GI epithelium.
E.g. Passive transport
What is Paracellular / Intercellular transport?
The transport through junctions between GI epithelium.
What is Vesicular / Corpuscular transport?
Give an example.
The transport of substances within vesicles into cells.
E.g. Endocytosis
Describe Endocytosis
It involves engulfing extracellular materials within a segment of the cell membrane to form a vesicle which is then pinched off intracellularly.
Substances that use Endocytosis.
Hint: Victoria Secret Fashion (model: KADE)
V: Vitamins (KADE)
S: Starch
F: Fats
Describe Exocytosis
The process of vesicles fusing with the plasma membrane and releasing their contents to the outside of the cell.
The 3 Phases of drug transfer from GI absorption site into systemic circulation are:
Hint: PUP
- Pre-uptake phase
- Uptake phase
- Post-uptake phase
Why is it that an adequate amount of drug doses must be delivered to target tissues?
So that Therapeutic, non-toxic levels are obtained.
Is having too little drug dangerous? State why.
a. Yes, will result in toxic effects.
b. Yes, will not result into the desired therapeutic effects.
c. No, there’s no effect
b. Yes, will not result into the desired therapeutic effects.
Why is too much drug dangerous?
Will result into toxic effects.
How does Lipid solubility of a drug influence absorption?
When drugs which are lipophilic easily cross the membrane, this increases absorption.
Why does absorption increase with non-ionized molecules (NaCI)?
Non-ionized molecules are lipid soluble , therefore they penetrate easily through the cell membrane.
Why does absorption decrease with ionized molecules (Na+, Cl-)?
Ionized molecules are water soluble, therefore they don’t penetrate easily through the membrane.
Lower pKa indicates a stronger acid. Therefore decreasing absorption.
Explain this statement…..
A stronger acid stays longer in the blood and binds to plasma albumin. Therefore decreasing absorption.
A higher pKa indicates a weak acid. Therefore increasing absorption.
Explain this statement…
Weak acid doesn’t bind to plasma albumin, meaning there are more free drugs. Therefore increasing absorption.
Basic drugs are better absorbed in _____ and better excreted in ____.
Basic media
Acidic media
Basic drugs are better absorbed in _____ and better excreted in ____.
Basic media
Acidic media
Why are acidic drugs better absorbed in acidic media?
Acidic drugs are more non-ionized in acidic pH.
Examples of weak acids
Hint: Phoebe
Phenobarbital
Pentobarbital
Examples of weak bases
Hint: Mc Donald
Morphine
Cocaine
3 drug properties that affects drug permeability are:
- Lipophilicity
- Polarity of drug
- Molecular size of the drug
Molecular size of a drug affects drug permeability by:
Smaller the molecule size, the greater the surface area of the membrane to absorb the drug.
Define Hydrate drugs
Drugs in association with water.
Define Anhydrous drugs
Drugs not in association with water.
3 Biological factors that influence absorption
- Surface area
- Food
- Destruction of drug in GIT
Surface area decreases or increases absorption?
The more absorptive surface area, the more absorption.
More drug absorption takes place in…
Small intestine
How does food decrease absorption?
Physiochemical properties of food products chemically binds to drug and converts to insoluble salt that is not easily absorbed.
How does food increase absorption?
Foods rich in fat improves the solubility of lipid soluble drugs.
Explain destruction of drug in GIT
In GIT, there are enzymes that can destroy drugs before absorption.
Eg. Benzylpenicillin is destroyed by gastric HCl.
