Definitions-General Pharmacology

Definitions-Pharmacokinetics

Absorption
The movement of a drug from the site of administration into the blood stream

pKa
The pH at which half of the drug is ionized and half of the drug 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

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 molecule 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 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 absorption and 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
Kinetics in which the pharmacokinetic processes become saturated

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

Maintenance Dose
The dose of drug required to sustain a desired steady state blood concentration of the drug OR
The dose of drug required to sustain a therapeutically effective blood concentration of the drug

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

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 drugs or one drug and one endogenous substance act upon two different receptors to produce opposite physiological actions

Pharmacological Competitive Antagonism
This is when one drug opposes the actions of another drug or endogenous ligand (which acts as an agonist) by competing with binding on the same site at the receptor as that of the agonist

Pharmacological Non-Competitive Antagonism (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
This is the study of inherited genetic differences in drug metabolic pathways which can affect individual responses to drugs, both in terms of therapeutic effect as well as adverse effects.

Pharmacogenomics
The study of the role of genetics in drug response

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
A specific condition in which a drug should not be used because it may be harmful to the patient

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

From “Nauman’s Textbook of Pharmacology”, 3rd Edition

Allied Book Company, Mall Road, Lahore, Pakistan

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