Chapter 2Basic Concepts of

Pharmacology

By : Sanjay Kumar

Chapter 2 Topics

• Receptors

• Mechanisms of Drug Action

• Pharmacokinetics

• Drug Effects

Learning Objectives

• Understand receptors and their function in mechanisms of drug actions.

• Be aware of the pharmacokinetics involved in developing and testing drugs.

• Understand that some drug effects are beneficial whereas others can be harmful.

• Be familiar with the common terms used to describe drug interactions.

Receptors

• A receptor is a protein molecule on the surface of or within a cell that recognizes and binds with specific molecules, thereby producing some effect within the cell.

Receptors

• A receptor is a protein molecule on the surface of or within a cell that recognizes and binds with specific molecules, thereby producing some effect within the cell.– receptor site may have specificity– the affinity is the strength by which a particular

chemical messenger binds to its receptor site or cell

Mechanisms of Drug Action

Agonist

An agonist is a drug that binds to a particular receptor site and triggers the cell’s response in a manner similar to the action of the body’s own chemical messenger.

Mechanisms of Drug Action

Antagonist

An antagonist is a drug that binds to a receptor site and blocks the action of the endogenous messenger or other drugs.

Pharmacokinetics

• Activity of a drug within the body over a period of time.

• Includes ADME

Pharmacokinetics

• Activity of a drug within the body over a period of time

• Includes ADME– absorption– distribution– metabolism– elimination

Pharmacokinetics

AbsorptionProcess whereby the drug enters the circulatory system

Pharmacokinetics

DistributionProcess by which a drug moves from the blood into other body fluids and tissues and ultimately to its sites of action

Blood flow is the rate-limiting factor.

Pharmacokinetics

MetabolismProcess by which drugs are chemically converted to compounds and then excreted through metabolic pathways.

Induction

Inhibition

Pharmacokinetics

EliminationClearance is the rate at which a drug is eliminated from a specific volume of blood per unit of time.

Discussion

What are the primary sites of elimination in the body?

Discussion

What are the primary sites of elimination in the body?

Answer: The kidney and the liver, but can also be exhaled by the lungs or excreted in perspiration.

Pharmacokinetics

Dose-Response Curve

Pharmacokinetics

Therapeutic Range

Pharmacokinetics

Duration of Action

Discussion

How is a drug’s volume of distribution, clearance, and half-life used in dosing drugs?

Discussion

How is a drug’s volume of distribution, clearance, and half-life used in dosing drugs?

Answer: Volume of distribution is important for calculating the loading dose, clearance for calculating the maintenance dose, and half-life for determining the dosing interval.

Pharmacokinetics

Pharmacokinetic ModelingMethod of describing the process of ADME of a drug within the body

Drug Effects

Beneficial Responses

Drug Effects

Beneficial Responses– Therapeutic Effect

The action for which the drug is prescribed

Drug Effects

Beneficial Responses– Therapeutic Effect

The action for which the drug is prescribed

– Local EffectConfined to a specific part of the body

Drug Effects

Beneficial Responses– Therapeutic Effect

The action for which the drug is prescribed

– Local EffectConfined to a specific part of the body

– Systemic EffectGeneralized, all-inclusive effect on entire body

Discussion

What are some of the issues a healthcare practitioner considers when selecting a drug for an individual patient?

Drug Effects

When choosing a drug for a patient, a healthcare practitioner considers:

IndicationsThe diseases, symptoms, and conditions for which the drug is known to be of benefit

ContraindicationsThe diseases, symptoms, and conditions for which the drug will not be beneficial and may do harm

Drug Effects

Side EffectsSecondary responses to a drug other than the primary therapeutic effect for which the drug was intended

• Allergic responses

• Drug dependence, addiction, abuse, and tolerance

Common Drug Relationships

Addition The combined effect of two drugs. It is equal to the sum of the effects of each drug taken alone.

Antagonism The action of one drug negates the action of a second drug.

Common Drug Relationships

Potentiation An effect that occurs when a drug increases or prolongs the action of another drug, and the total effect is greater than the sum of the effects of each drug used alone.

Synergism Joint action of drugs in which their combined effect is more intense or longer in duration than the sum of their individual effects.

Discussion

Name a common food-drug interaction.

Discussion

Name a common drug-food interaction.

Answer: Grapefruit juice can affect drugs for up to a day following ingestion.

Discussion

Why is it important for the pharmacy to have a complete list of all of the prescription drugs, OTC medications, vitamins, and herbal remedies that a patient is taking?

Discussion

Why is it important for the pharmacy to have a complete list of all of the prescription drugs, OTC medications, vitamins, and herbal remedies that a patient is taking?

Answer: Such a list will help healthcare professionals identify potential drug interactions.