Pharmacokinetics Flashcards
How must drugs travel from the point of entry to the brain?
Through the circulatory system
What influences how much of a drug gets to the brain and how fast it gets there?
The ability of the drug to travel through the body and reach the brain intact
What is pharmacokinetics?
Refers to the processes involved in the movement of drugs within biological systems with respect to absorption, distribution, metabolism, and excretion
What determines how big of an effect a drug will have?
Molecular structure of the drug (hydrophobic/hydrophilic), concentration of the drug at the site of action, dose administered, rate of accumulation
What is pharmacodynamics?
The biochemical and physiological effects of drugs and their mechanisms of action
Which term refers to the effects of drugs on the body and also the effects of the body on the drug?
1) pharmacodynamics
2) pharmacokinetics
What is absorption?
Refers to getting the drug from where it needs to go to the site of action (brain)
Drugs must pass through barriers before entering into the ______
Bloodstream
True or false: Drugs are generally too large to go through ion channels
True
What factors related to drugs influence absorption?
A lot of things, but the main three things are lipid water solubility, dosage forms, and concentration
What factors related to the body influence absorption?
Surface area of absorptive surface, vascularity, pH, presence of other substances, GI motility, functional integrity of surface, diseases
What influences how well a drug passes through a membrane?
Concentration and lipid/water solubility though the latter is the most important factor
Most drugs are soluble to some extent in both water and lipids. Why is this?
They need to be hydrophobic enough to cross membranes but hydrophilic enough to be transported through the bloodstream
What is the oil-water partition coefficient?
The relative solubility between oil and water = oil/water
What do higher oil-water partition coefficients mean?
That the molecule can more readily cross the membrane and dissolves less easily in water
The number of barriers a drug must go through depends on the _________
Route of administration
What are the 4 common routes of drug administration?
1) oral
2) injection
3) inhalation
4) absorption through the skin/membranes
What are three ways someone could inject a drug?
1) intravenous
2) subcutaneous
3) intramuscular
What are the 2 ways someone can inhale a drug?
1) smoking
2) vapor inhalation
What are the 3 ways someone can absorb a drug through the skin/membranes?
1) intranasal
2) sublingual
3) transdermal
Why is oral administration a long, dangerous journey?
In the stomach, drugs must withstand the stomach acid and degrading enzymes. Also, the drug must pass through the cells lining the walls of the GI tract. The majority of substance from the GI tract is sent to the liver where degrading enzymes are present.
What is the first pass effect?
This effect only applies to drugs taken orally and means that the drug is sent directly by the blood after GI tract to the liver for metabolism
Why is oral administration not good in the case of emergency?
It is the slowest of the routes and reduces the concentration of the drug by the time it reaches target tissues
If the movement of your GI tract is quicker, will more or less drug be absorbed?
Less will be absorbed because there is less time of contact
Are you more likely to absorb more drug on an empty stomach or a full one?
An empty stomach
Describe the logistics of the IV injection method of drug administration.
Here the drug bypasses all barriers and goes directly into the bloodstream. Faster onset and higher concentrations of drug compared to oral admin. Can be toxic or lethal.
What are the disadvantages of IV administration?
1) drug has to be in solution
2) weakens veins
3) can cause blood clots
4) dangerous (bacteria, diseases)
5) hard to stop IV overdoses
What is intramuscular injection, and how does its speed compare to other methods?
Drug injected into muscle, faster onset than oral but slower than IV
What is subcutaneous injection, and how does its speed compare to other methods?
Drug is injected under the skin into the fat, slower than IM and IV
What is inhalation, and how does its speed compare to other methods?
Breathing it in through the lungs, very fast and sometimes faster than IV, produces intense effects, lungs have a large surface area and can not only absorb more but they are in close proximity to blood vessels
Describe how sublingual/intranasal administration works.
Muscous membranes absorb the drug in the mouth or nose, they have rich blood supply. Drugs dissolve in mucous or saliva and enter blood supply
What is the final barrier? How does it regulate things?
The BBB; must be very small, compatible with an active transport system, and lipid soluble
True or false: Sometimes, the same drug taken
via different routes of
administration, will have
different intensities of effect.
True
Why should we care about routes of administration?
The faster the absorption, the more intense the high. The more intense the high, the greater the likelihood of addiction
Why is there a cultural issue with cocaine in the United States?
Methods used are the more likely to be addicting ones
Why do drugs tend to accumulate in tissues other than their sites of action?
Due to lipid solubility
The sites of accumulation of drugs are often where they cause _______
Toxicity
Why are psychoactive drugs stored in fat tissues?
Storage depot of lipids
What is metabolism?
Refers to any process that results in chemical change in a drug in the body
What effects can metabolism have on a drug?
Can make it less or more active or have no effect
Where is the major site of drug metabolism?
The liver
What is the hepatic microsomal enzyme system?
An enzyme system that has evolved to deal with toxic substances
Why are the enzymes of the hepatic microsomal enzyme system non-specific in nature?
They were developed to respond to a wide array of various chemicals
Some drugs have specific enzymes that metabolize only that drug. Name an example of this.
Alcohol
When drugs are metabolized in the liver, what are they turned into?
Water soluble metabolites
Where are water soluble metabolites passed after processing by the liver?
Into the urine
What is a plasma half-life of a drug?
The amount of time it takes to eliminate half of the drug from the bloodstream
When are the kidneys most efficient at excreting drugs?
When the concentration is high
Most drugs are removed from the body through what organ?
Kidneys
For most drugs, the higher the concentration, the ______ the excretion.
Faster
What is the half life of nicotine?
30 minutes
Since psychoactive drugs are lipid soluble, excretion is very ____.
Slow
What does excretion depend on?
The acidity of the drug and the acidity of the urine
If you want to increase the excretion of an acidic drug like aspirin, what is a good thing to consume?
Soda because bicarbonate is basic
If you want to increase the excretion of a basic drug like morphine, what is a good thing to consume?
Vitamin C because it makes the urine more acidic
What are the 4 parts of pharmacokinetics?
Absorption, distribution, metabolism, excretion
