Basic pharmacology Flashcards
What is pharmacology?
The science of drugs or the science that deals with the effects of drugs on living systems
What is medical pharmacology often defined as?
The science of substances used to prevent, diagnose and treat disease
What is a drug?
A drug is any substance or product that is used or intended to be used to modify or explore physiological systems or pathological states for the benefit of the recipient
What are the two main divisions of pharmacology?
Pharmacokinetics
Pharmacodynamics
What is pharmacodynamics?
The study of the mechanism of action of a drug, its pharmacological actions and its adverse effects (what a drug does to the body)
It also studies the dose/response relationship
What are the 4 parts of pharmacokinetics?
Absorption
Distribution
Metabolism
Elimination/excretion
What are the 2 main parts of pharmacodynamics?
Efficacy
Toxicity
What can the main types of drug action be broadly classified as?
Stimulation
Depression
Irritation
Replacement
Cytotoxic action
What is pharmacokinetics?
The movement and alteration of a drug within the body, “what the body does to the drug”
What is drug absorption?
The movement of a drug from site of administration into systematic circulation
What factors affect drug absorption?
Physical state
Particle size
Disintegration
Lipid/water solubility
Drug pH
Chemical nature
Concentration
Route of administration
Area of absorption surface
Vascularity
Presence of other substances (food, drugs etc.)
Gastrointestinal and other diseases
Are liquid or solid forms of drugs absorbed faster?
Liquid
Are lipid or water soluble drugs absorbed greater?
Lipid soluble
What pH drugs are better absorbed?
Weak acids and weak bases are better absorbed that strong acids and strong bases
Where are acidic drugs absorbed from?
The stomach
Where are basic (alkaline) drugs better absorbed?
The intestine
When are salt forms of drugs better absorbed than organic compounds?
When administered orally
What is bioavailability?
The rate and extent of absorption of a drug from a dosage form as determined by its concentration-time curve in the blood i.e. the fraction of a drug that reaches systemic circulation from a given dose
What route of drug administration gives 100% bioavailability?
Intravenous
Why does the oral route give lower bioavailability?
The drug may be incompletely absorbed
First pass effect
What is drug distribution?
The reversible transfer of drugs between body fluid departments (the extracellular fluid and tissues)
What happens after drug absorption?
It enters the systemic circulation and is distributed in body fluids
What immediately follows intravenous drug administration?
Distribution, as there is no initial absorption
What does drug distribution from the plasma to the extracellular fluid depend on?
Cardiac output
Binding of drugs to plasma proteins
Binding of drugs to tissue proteins
Lipophilicty
Why do many drugs accumulate in tissues and why is this relevant?
Binding to tissue proteins. Tissue reservoirs may serve as a major source of the drug and prolong its actions or it may cause local drug toxicity
Why is lipophicililty relevant to drug distribution?
Lipophilic drugs readily move across most biologic membranes. By contrast, hydrophilic drugs do not readily penetrate cell membranes and must pass through pores in the capillary wall
What is drug redistribution?
Redistribution refers to the change in the plasma drug concentration which is significant enough to cause alteration/termination of drug action.
When and how does drug redistribution happen?
When a highly lipid-soluble drug gets initially distributed to organs with high blood flow (brain, heart, kidney etc.).
Later less vascular but more bulky tissues take up the drug
This causes a fall in the plasma concentration and the drug is withdrawn from the highly perfused sites - if the site of action is one of these highly perfused tissues this can cause alterion/termination of drug action
Why is lipid solubility of a drug relevant to redistribution?
The greater the lipid solubility of the drug, the faster its redistribution
What is drug elimination?
The irreversible removal of a drug from the body which involves:
-Metabolism (bio transformation)
-Excretion
These elimination processes decrease drug concentration in plasma (clearance) exponentially
What does drug biotransformation mean?
Chemical alteration of the drug in the body
Why is drug metabolism (bio transformation) neede?
To convert nonpolar (lipid soluble, unionised) compounds to polar (water-soluble, ionised) compounds so that they are not reabsorbed in the renal tubules and are excreted
i.e. metabolism results in products with increased polarity, which allows the drug to be eliminated
What type of drugs are little biotransformed (may not get metabolised) and are largely excreted unchanged?
Most water-soluble drugs
What are the main and other sites for drug metabolism?
The main site is the liver, others include the GI tract, kidneys, lungs, blood, skin and plasma
What may drug bio transformation lead to?
Inactivation
Active metabolite from an active drug
Activation of inactive drug
What is a prodrug?
An inactive form of a drug which is converted to active after metabolism
What are the advantages of pro-drugs over active forms?
More stable
Better bioavailability
Other desirable pharmacokinetic properties
Less side effects and toxicity
What are the main and other routes of drug excretion?
The main channel is the kidneys, others include the lungs, faeces, bile, sweat, saliva, tears, milk etc.
Why are patients with renal dysfunction at risk of drug accumulation and adverse affects?
The kidneys are the most important channel of excretion for the majority of drugs
What substances are excreted via the lungs?
Gases, alcohol and volatile liquids
How are unabsorbed fractions of drugs removed from the body?
Via faeces, other metabolites excreted by this route are derived from the liver and bile.
What happens to some drugs excreted via bile?
After reaching the intestine they may be reabsorbed into the circulation, increasing drug bioavailability as well as their duration of action
Of what importance for drug excretion are saliva and sweat?
Most of the saliva along with the drug in it is swallowed and meets the same fate as an orally taken drug
Who is the excretion of drugs via milk important for?
Not important for the mother, but the suckling infant inadvertently receives the drug
Can you give drugs to lactating mothers and why?
The amount reaching the infant is generally small so the majority of drugs can be given to lactating mothers without ill effects on the infant. Nevertheless, it is advisable to administer any drug to a lactating woman only when essential
What is the half life (t1/2) of a drug?
Half-life of a drug means the period if time required fir the concentration or amount of the drug in the plasma to be reduced by one-half
What is the volume of distribution of a drug?
The distribution of the drug in the various body tissues
How is drug clearance calculated?
The volume of blood from which the drug is cleared per unit of time
What happens to drugs once they leave the plasma?
They can be:
Eliminated from the body
Translocated to another body fluid compartment such as the intracellular fluid
It can be destroyed in the blood
What can drug plasma half time help to determine?
-The duration of action
-The frequency of drug administration
-Estimate the time required to reach the steady state (constant levels in plasma and tissue)
How do drugs with short half-lives need to be administered?
In regular doses to build up and maintain a high enough concentration in the blood and tissue
What is the mechanism of action of a drug?
How the drug works on the molecular level in the body
What are the two types of drug mechanism of action?
Non-receptor mediated mechanism
Receptor mediated mechanism
What non-receptor mediated drug mechanisms of actions are there?
Physical action e.g. osmosis, absorption, soothing effect, radioactivity
Chemical action e.g. antacids
Inhibiting enzymes e.g. ACE inhibitors
Antibody production e.g. vaccines
What is drug affinity?
The ability of the drug to bind to the receptor
What is intrinsic activity?
The ability of the drug to produce a pharmacological action after binding to the receptor
What is an agonist drug?
A drug that can produce a pharmacological action after binding to the receptor (affinity + intrinsic activity)
What is an antagonist drug?
A drug that prevents the binding of an agonist to its receptor or block its effect. It does not produce any effect by itself
What is a partial agonist?
A drug that binds to the receptor but produces an effect less than that of an agonist. Usually it inhibits the affect of an agonist
What is an inverse agonist?
A drug that has full affinity towards a receptor but produces an effect opposite to that of an agonist
