Session 7: Pharmacokenetics Flashcards
What are the 2 ways in which drugs are taken into the body?
Adsorption
Distribution
What are the 2 ways in which drugs are removed from the body?
Metabolism
Elimination
What is enteral administration?
Delivery into the internal environment of the body i.e. the GI tract
- Oral
- Sublingual
- Rectal
What is parenteral administration?
Delivery via all other routes that aren’t the GI tract
- Intravenous
- Subcutaneous
- Intramuscular
TRUE OR FALSE: There is little adsorption in the stomach.
True:)
Where does the majority of adsorption take place?
Small intestine
Name 2 ways in which drugs can be absorbed.
- Passive Diffusion
2. Facilitated diffusion
What sort of drugs are adsorbed by passive diffusion?
Lipophilic drugs that are weak acids/bases which diffuse directly down their concentration gradients
What sort of drugs are adsorbed by facilitated diffusion?
OATs (organic anion transporters) and OCTs (organic cation transporters) are solute carrier proteins (SLC) that transport molecules with nett charges
Name 3 physiochemical factors affecting drug absorption.
- GI length/SA
- pKa of drug
- Density of SLC expression
Name 3 GI physiology factors affecting drug absorption.
- Blood flow
- GI motility
- Food iPh
What is meant by first pass metabolism?
It is a phenomenon of drug metabolism whereby the concentration of a drug is greatly reduced before it reaches the systemic circulation.
What are the 2 main enzyme groups that are responsible for first pass metabolism by the GI and the Liver?
- Cytochrome P450s - Phase I enzymes
2. Conjugating - Phase II enzymes
Where is their larger expression of Phase I and phase II enzymes?
The liver
What is bioavalibility?
Fraction of a defined dose which reaches its way into a specific body compartment.
How is Oral Bioavailibility (F) calculated?
Amount reaching systematic circulation/total drug given IV (calculate the area under the curves) which gives a result between 0 and 1
How can a drug reservoir in the body be established?
Drugs may bind to plasma and/or tissue proteins decreasing the drug availability for binding.
What is apparent volume of distribution? (Vd)
A model used to provide a summary measure of drug molecule behaviour during distribution.
(Summarises movement out of plasma -> interstitial -> intracellular compartment)
What can be implied by a small Vd value?
less penetration of interstitial/ intracellular fluid compartment
How many superfamilies of cytochrome P450 enzymes are there?
3 (they do not show overlap)
Name 5 factors affecting drug metabolism.
- Age
- Sex
- disease (i.e. especially hepatic renal CVS
- drugs which inhibit or induce CYP450s
- CYP450 polymorphism (genetic variation)
What is clearance? (CL)
The rate of elimination of a drug from the body
What is the sum for clearance? (CL)
Hepatic clearance + Renal clearance
What is drug half life? (t1/2)
The amount of time over which the concentration of a drug in plasma decreases to one half of its value of when it was first measured.
What is meant by first order (linear) elimination kinetics?
The rate of metabolism is proportional to the concentration of the drug.
What are the conditions of first order (linear) kinetics?
- Plenty of phase I/II enzymes
- Plenty of OCTs/ OATs
What happened when an elimination process becomes saturated?
The rate becomes limited (referred to as zero order kinetics)
