Definitions-General Pharmacology
Definitions-Pharmacokinetics
Absorption
The movement/transfer of a drug from the site of administration to the blood stream
pKa
The pH at which half of the drug is ionized and half is unionized.
Bioavailability
The fraction or percentage of drug reaching the systemic circulation in a chemically unchanged form following administration by any route.
OR
The rate and extent of drug reaching the systemic circulation in a chemically unchanged form following administration by any route
First Pass Elimination
Elimination (metabolism and excretion) of a drug before it first reaches the systemic circulation
Extraction Ratio
A measure of efficiency of an organ in eliminating a drug during a single passage through it
Hepatic Extraction Ratio
The fraction of drug that is eliminated during a single passage through the liver or
The fraction of drug removed from the blood in one passage through the liver
Bioequivalence
The property wherein two proprietary/brand formulations of a drug possess similar bioavailability
Therapeutic Equivalence
The property wherein two drugs with identical active ingredients or two different dosage forms of the same drug produce similar efficacy & toxicity when given in the same doses
Distribution
It is the process by which a drug reversibly leaves the blood stream and enters the interstitial fluid and/or the cells of the tissues
Redistribution
Movement of a drug from site of action to other sites (or a site of non-action)
Volume of Distribution
The volume that would accommodate all the drug (D) in the body if the concentration (C) throughout was the same as that in plasma”
OR
The volume of fluid required to contain the total amount of drug in the body at the same concentration as that present in the plasma
Biotransformation
The chemical alteration that a drug undergoes in the body with a consequent change in its solubility and activity
Enzyme Induction
A process in which a substance e.g. a drug induces (initiates or enhances) the expression of (metabolic) enzymes
OR
A process in which a drug increases the synthesis and activity of a metabolic enzyme by increasing its expression
Enzyme Inducer
A drug that induces (initiates or enhances) the expression of drug metabolizing enzymes
OR
A drug that increases the synthesis and activity of drug metabolizing enzyme by increasing its expression
Enzyme Inhibition
A process in which a drug decreases/inhibits the activity of a drug metabolizing enzyme
Enzyme Inhibitor
A drug that inhibits the activity of a drug metabolizing enzyme
Plasma Half-Life
The time it takes for plasma concentration of a drug to be reduced to 50% of its initial value
First Order Kinetics
Kinetics in which a constant FRACTION of drug is absorbed, distributed, metabolized and excreted per unit time
OR
Kinetics in which the rate of elimination of a drug is directly proportional to the concentration of the drug
Zero Order Kinetics
Kinetics in which a constant AMOUNT of drug is absorbed, distributed and eliminated per unit time
Steady State Plasma Concentration
This is the plasma concentration reached by a drug at a time when its rate of administration is equal to its rate of elimination
Elimination Rate Constant (Ke)
This is the FRACTION of drug in the body that is eliminated per unit of time
Maintenance Dose
It is the dose of a drug required to maintain a desired target plasma concentration in order to sustain a specific therapeutic effect’
Loading Dose
A larger dose of drug administered so as to achieve steady state plasma concentration more quickly than by giving maintenance dose
Drug Excretion
The irreversible transfer of a drug and/or its metabolites from the tissues and/or blood to the external environment.
Clearance
The volume of plasma cleared of a substance/drug per unit time
Definitions-Pharmacodynamics
Pharmacodynamics
Study of biochemical and physiological effects of drugs and their mechanisms of action
Receptor
The component of a cell or organism that interacts with a drug and initiates the chain of events leading to the drug’s observed effects
Any functional macromolecule in a cell to which a drug binds to produce its effects
Effector
Component of the biological system that accomplishes the biological effect after being activated by the receptor
These are molecules that translate the drug-receptor interaction into a change in cellular activity
Efficacy or Intrinsic Activity
The ability of a drug to elicit a response when it interacts with a receptor
Ability of the drug-receptor complex to activate the receptor i.e. ability to initiate one of the post-receptor transduction mechanisms
The maximal effect that can be achieved with a particular drug, regardless of dose
Potency
Amount (dose or concentration) of drug required to produce a certain magnitude of effect
The concentration (EC50) or dose (ED50) of a drug required to produce 50% of that drug’s maximal effect
Agonist
Drugs that interact with a receptor and thereby initiate a cellular reaction
A drug that has affinity as well as efficacy
Full Agonist
A drug capable of fully activating the effector system when it binds to the receptor
A drug that has affinity to bind with receptor as well as maximum efficacy even without the occupancy of all the receptors
Partial Agonist
A drug that has affinity and efficacy but efficacy is less than that of a full agonist even with the occupancy of all the receptors
Inverse Agonist
A drug that has affinity and efficacy but the effect produced is opposite to that of an agonist
Antagonist (Receptors)
A drug that has affinity but no efficacy / intrinsic activity.
Antagonism
The phenomenon in which one drug opposes the action of another drug or an endogenous substance
Antagonist
Antagonists are drugs that decrease or oppose the actions of another drug or endogenous ligand.
Chemical Antagonism
This is when one drug opposes actions of another by chemical means i.e. by binding to, inactivating, or neutralizing target compounds
Physiological Antagonism or Functional Antagonism
This is when one drug opposes the actions of another drug or an endogenous substance by opposing agonistic actions on different receptors
OR
This is when two agonists upon two different receptors to produce opposite physiological actions
Pharmacological Competitive/Reversible Antagonism
This is when one drug opposes the actions of an agonist by competing with binding on the same site on the same receptor as that of the agonist
Pharmacological Irreversible Antagonism
This is when one drug opposes the actions of an agonist by irreversibly binding (by strong covalent bond) on the same site on the same receptor as that of the agonist
Pharmacological Allosteric Antagonism
This is when one drug opposes the actions of another drug or endogenous ligand (which acts as an agonist) by binding to a different site (allosteric site) on the same receptor as that of the agonist
Dose Response Curve
A graph that depicts the relationship of dose to response
Graded Dose Response Curve
A graph that determines the effect of a drug as a function of its dose
Quantal Dose Response Curve
A curve that describes the distribution of MINIMUM doses of drug required to produce a defined degree of a specific response in a population of subjects.
A graph that depicts the fraction of the population that responds to a given dose of drug as a function of the drug dose
EC50
The concentration of a drug that produces half of the maximum effect (EMax)
ED50 (For graded dose response curve)
The DOSE of a drug required to produce half of the maximum effect (EMax)
Kd
The concentration of free drug at which half of the receptors are occupied
Spare Receptors
Receptors are said to be “spare” for a given pharmacologic response if it is possible to elicit a maximal biologic response at a concentration of agonist that does not result in occupancy of the full complement of available receptors
Median Effective Dose ED50 (For Quantal dose response curve)
The dose of a drug that produces the specific required effect in 50% of the test population
The dose at which 50% of individuals exhibit the specified desired effect
Median Lethal Dose (LD50)
The dose of a drug that produces lethal effect (death) in 50% of the test population
Median Toxic Dose (TD50)
The dose of a drug that produces the specific toxic effect in 50% of the test population
The dose at which 50% of individuals exhibit the specified toxic effect
Therapeutic index
In animal studies, the therapeutic index is the minimum lethal dose of a drug for 50% of the population (LD50) divided by the minimum effective dose for 50% of the population (ED50).
Margin of Safety
This is the ratio between the dose that produces death (LD50) in 0.1 % of the population to the dose that produces the desired effect (ED50) in 99.9% of the test population
Clinical Therapeutic Index
This is the ratio between the dose that produces a specified toxic effect (TD50) to the dose that produces the desired effect (ED50) in 50% of the test population
Therapeutic Window
The range between the minimum effective therapeutic dose or concentration and the minimum toxic dose or concentration
Pharmacogenetics
Branch of pharmacology devoted to the study of variation in drug response due to genetic factors.
Pharmacogenomics
The branch of genetics concerned with determining the likely response of an individual to therapeutic drugs
Tolerance
Gradual decrease in the response to a drug upon repeated administration over a long period of time
Cross Tolerance
This occurs when repeated use of a drug in a given category confers tolerance not only to that drug but also to other drugs in the same structural and mechanistic category.
Tachyphylaxis
Rapid decrease in the response to a drug after only a few doses over a short period of time; An acute (sudden) decrease in the response to a drug after only a few doses
Receptor Down Regulation
Decrease in number of receptors brought about by prolonged exposure to an agonist
Receptor Upregulation
Increase in number of receptors brought about by prolonged exposure to an antagonist
Desensitization
Receptors become desensitized when they no longer respond to continued exposure to an agonist;
Refractoriness
This is the progressive loss of therapeutic efficacy often by physiological adaptation e.g. refractoriness shown by diuretics
Idiosyncrasy
Idiosyncrasy is an abnormal unexpected response to a drug mostly mediated by genes and that causes increased, decreased or bizarre responses to a drug.
Drug Interaction
This is when the effect of one drug is altered by the presence of another drug in the body
Modulation of pharmacological activity of one drug (the object drug) by concomitant administration of another drug (the precipitant drug)
Contraindication
Any condition in which a drug or group of drugs should not be used because it may result in undesired effects
Drug Dependence
WHO has defined drug dependence as “ A state, psychic and sometimes physical, resulting from the interaction between a living organism and a drug, characterized by behavioral and other responses that always include a compulsion to take the drug on a continuous or periodic basis in order to experience its psychic effects and sometimes to avoid the discomfort of its absence. Tolerance may or may not be present. A person may be dependent on more than one drug.”
Addiction
Compulsive, relapsing drug use despite negative consequences, at times triggered by cravings that occur in response to contextual cues
A severe form of drug dependence in which a person has an extreme craving for the drug of abuse and spends most of his daily activities in obtaining that drug somehow or another
Adverse drug reaction (ADR)
WHO definition: “Any response to a drug that is noxious and unintended and that occurs at doses used in man for the prophylaxis, diagnosis or therapy of disease or for modification of physiological function”
Unintended and unexpected effect occurring at normal dose unrelated to the pharmacological action(s) of the drug
Teratogen
A drug or other substance capable of causing structural and/or functional birth defects
Orphan Drug
These are drugs or biological products for diagnosis, treatment, and/or prevention of life-threatening or chronically invalidating rare diseases from which no more than 5 in 10,000 people suffer.
For more details and other useful information on Pharmacology
Read ‘Nauman’s Textbook of Pharmacology’ (3rd Edition)
For comprehensive classification of drugs :
For many more MCQs (4500 MCQs) divided into units, chapters, and topics read:
‘Learning Pharmacology from Nauman’s MCQS’