Chapter 1 Flashcards
What is a drug?
Complicated to define. Any substance that alters the physiology of the body that is not a food or nutrient works, but is still not complete. An intuitive definition works.
What are the three names a drug has?
1: Chemical Name - the chemical composition of the drug stated in chemistry jargon. Different conventions of for numbering where molecules connect, which complicates matters.
2: Generic Name - Chemical name is too clumsy, so a naming council names the drug with a generic (non-proprietary) name, usually based on the chemical name. Often, the stem will be an indicator as to what the drug does.
3: Trade Name - The patented name a company gives their drug which no other drug company can use. After patent expires other companies can produce drug, but usually under a different name, so one drug can have many trade names
(4) Street Names - Recreational drugs that are sold on the street are given street names that differ geographically. E.g., Ecstasy for MDMA.
Describe Dosages
Always presented in metric (all of science uses metric) (milligrams).
Behavioural and physiological effects of a drug are related to its concentration in the bod rather than the absolute amount of drug administered
Need different dosages for different body sizes so that concentration in the body is the same for everyone. Therefore, dosages are presented in milligrams per kilogram. E.g., 6.5 mg/kg.
Smaller organisms have higher metabolic rates and therefore need higher dosages. E.g., a 1mg/kg dose for a human would need to be 10mg/kg in rats.
What is a dose response curve (DRC)?
Give a wide range of doses (some so low you don’t see an effect, others so high there is no more increase in effect, and others in between). Plot these on a graph with the dose on the horizontal axis and the effect on the vertical axis.
E.g., dose of caffeine on the bottom, and lever pressing behaviour of a rat on the vertical.
Often you will see small changes at low doses gives a big effect, but an equal change at high doses does not see any change in effect.
What if the behaviour plotted on a DRC is not continuous, but binary?
Give different groups different dosages, then plot the percentage within each group that showed an effect.
What is the ED50 and LD50?
The ED50 is the median effective dose, that is, the dose that is effective in 50% of subjects.
The LD50 is the median lethal dose, that is, the dose that kills 50% of subjects.
Can use this to describe other percentages, such as the ED99 and LD1
What is used to describe the safety of a drug?
The distance between the ED50 and LD50 (the farther the effective dose is from the lethal dose, the safer the drug)
&
The Therapeutic Index (TI). The ratio of the LD50 to the ED50.
TI = LD50/ED50. The higher the TI, the safer the drug.
Describe Potency and Effectiveness
Both describe the extent of the drug’s effect.
Potency refers to the differences in the ED50 of two drugs. The drug with the lower ED50 is more potent.
If one drugs ED50 is 10 times higher than another drug, you would need to take that drug at 10 times the dose of the other to get the same effect.
Effectiveness refers to differences in the maximum effect that drugs will produce at any dose.
For example, the same dose of Aspirin will not be as effective at decreasing pain as the same dose of morphine.
What are primary effects and side effects?
The primary effect is the effect that the drug is being taken for, and side effects are all other effects the drug produces.
Aspirin has many different uses, such as analgesia, reducing fever, etc. If you take Aspirin to reduce pain, analgesia is the primary effect, fever reduction is a side effect. If taken to reduce fever, analgesia is now the side effect.
Describe antagonism as it refers to drug interactions
Antagonism is when one drug diminishes the effectiveness of another drug.
We figure this out by plotting two DRC curves, one with the drug alone, the other with the two drugs combined. If the ED50 of the two drugs combined shifts to the right (ED50 increases), then it is antagonistic.
Describe additive and super-additive effects
When the shift of the ED50 for both drugs combined shifts to the left, it has an additive effect.
If it shifts farther to the right than would be expected by adding both drugs, it is super-additive.
When one of the drugs is not known to have an effect, but it shifts the ED50 of both drugs combined to the left, you know that it is super-additive.
What is Pharmacokinetics?
The study of how drugs move into, get around in and are eliminated from the body.
What are the three processes of Pharmacokinetics?
- Absorption: how the drug gets into the body;
- Distribution: where the drug goes in the body;
- Elimination: how the drug leaves the body.
What is a site of action?
Where the drug influences the operation of the body. Most drugs do not effect all body tissues, but rather influence specific and limited places.
A drug may get into the body, but not have any effect unless it reaches it’s site of action.
What are the four major overarching methods of administration?
- Parenteral - (i.e., injection);
- Inhalation;
3: Oral;
4: Transdermal.
What is a “vehicle” as it relates to parenteral administration?
The form that can pass through a syringe/needle - must be in liquid form. The drug is suspended in this liquid. Most drugs suspended in 0.9% sodium chloride water (saline solution).
Some drugs, such as THC must be in vegetable oil because they can not be suspended in saline.
What are the four parenteral routes of administration?
- Subcutaneous - s.c. (under the skin);
- Intramuscular - i.m. (into the muscle);
- Indra-peritoneal i.p. (into the peritoneal cavity);
- Intravenous i.v. (into a vein/into blood stream).
List the factors involved in absorption from parenteral sites of administration.
Blood flow to the area of administration (fastest in i.v. as it goes directly into blood stream, then i.p., then i.m., then s.c.).
Heat and exercise - this causes an increase in blood flow, quickening absorption.
Diffusion through capillary walls (movement from high concentration to low concentration).
Areas with more capillaries therefore absorb drugs faster than areas with fewer capillaries.
What are depot injections?
For drugs that need to be taken continuously and/or chronically, the drug can be suspended in an oil solution that dispenses the drug over a very long period of time (e.g., a month). Drug must be highly lipid soluble.
What are the two methods of inhalation?
- Gases;
2. Smoke and solids.
Explain how gases are absorbed.
Air enters lungs, which have a lot of surface area due to bronchi and bronchioles. This surface area is lined by capillaries, so that oxygen and carbon dioxide diffuse through to enter and escape the circulatory system respectively. Drug in gas form diffuses through walls of capillaries into the blood stream.
What is the major difference between gases and smoke/solids?
The drug in the smoke particles for smoke and solids will not re-vaporize after it is dissolved in the blood, and therefore can not be exhaled. They will stay in the body until they can be eliminated by other means.
Describe how drugs are absorbed when taken orally.
The drug enters the stomach, where digestion begins. Some drugs can be absorbed here if they are soluble in gastric fluids and resistant to enzymatic breakdown in the stomach.
Most drugs are absorbed in the intestines. The intestines are lined with capillaries that absorb nutrients from food and the drug. Drug must pass through wall of intestine to get to capillaries. The intestine wall is made up of a lipid bi-layer, therefore, the absorption of the drug depends on how lipid soluble it is.
Describe lipid solubility as it relates to absorption of drugs taken orally.
Different drugs have different degrees of lipid solubility that are usually expressed in terms of the “olive oil partition co-efficient”.
Drugs vary in lipid solubility in their normal state, but when a molecule of the drug carries an electric charge it can not dissolve in lipids (a negatively charged particle is called an Ion). When the drug is dissolved in a liquid, some or all of its molecules become ionized.
