Pharmacology Session 8.2: Membranes and Receptors

Podcast

Play an AI-generated podcast conversation about this lesson

Questions and Answers

What is meant by Emax in the context of spare receptors?

The maximum concentration of a drug

The point at which receptors are fully occupied

The effective concentration for 50% of the maximal response

The maximum response achievable by an agonist (correct)

What clinical benefit do spare receptors provide in cases of pathological receptor down-regulation?

They require higher drug dosages.

They ensure maintained drug efficacy. (correct)

They decrease receptor sensitivity.

They enhance drug metabolism.

Which statement accurately describes a partial agonist?

Has an EC50 greater than its Kd.

Always produces the maximal effect.

Never occupies all available receptors.

Can act as a full agonist in some tissues. (correct)

What is the relationship between potency and the number of receptors?

The number of receptors also influences potency. Signup and view all the answers

What characterizes reversible competitive antagonism?

Dynamic equilibrium between agonists and antagonists Signup and view all the answers

What does IC50 represent in pharmacology?

The concentration of antagonist giving 50% inhibition Signup and view all the answers

Which of the following is NOT a type of antagonist?

Non-Specific Antagonism Signup and view all the answers

What occurs when an agonist achieves Emax at subBmax?

The presence of spare receptors is confirmed. Signup and view all the answers

What does the term 'affinity' refer to in drug-receptor interactions?

The strength of drug binding with its receptor Signup and view all the answers

Which of the following statements about agonists is true?

Agonists have both affinity and efficacy Signup and view all the answers

What is the primary purpose of antagonists in pharmacology?

To prevent receptor activation by agonists Signup and view all the answers

How does drug concentration affect drug response?

It is generally proportional to the number of receptor sites bound Signup and view all the answers

What is defined as the ability of a drug-bound receptor to produce a response?

Efficacy Signup and view all the answers

Which of the following is NOT a characteristic of a drug's target receptor?

Receptors cannot bind to non-endogenous ligands Signup and view all the answers

What governs the binding of a drug to its receptor?

Association and dissociation Signup and view all the answers

In the context of drug action, what does potency refer to?

The concentration of drug required to achieve a specific effect Signup and view all the answers

Study Notes

Membranes and Receptors - Session 8.2

The lecture aims to provide an understanding of drug-receptor interactions to aid in clinical practice.
The quantitative relationship between drug concentration and response, agonist and antagonist drug action will be discussed.
Key terms that will be defined include: affinity, efficacy, potency, agonist, antagonist, and partial agonist.

Drugs and Their Targets

Medical pharmacology is the study of how chemicals (drugs) interact with the human body.
Many drugs exert their effects by interacting with targets, predominantly proteins.
Some antimicrobial and antitumor drugs bind to DNA.

Pharmaceutics, Pharmacodynamics, and Pharmacokinetics

Pharmaceutics: drug formulation for a specific route of administration.
Pharmacodynamics: interactions between a drug and its target (e.g., a receptor). Outcomes include efficacy, Emax, E, Bmax, B, potency, TD50, and TI.
Pharmacokinetics drug + body tissue interactions (apart from D+T). Outcomes include ADME (absorption, distribution, metabolism, and elimination).

Drug-Target Interactions

Many drug targets are receptors.
A receptor is a protein with a site for binding endogenous ligands (e.g., steroid receptors).
If a drug binds to a non-endogenous ligand site, this site is called an acceptor (e.g., enzyme blocker).

Receptor Types

Receptors come in various types.
Ion Channels: Direct mechanisms - opening/closing ion channels.
Enzymes: inhibit reaction and produce active drugs.
Transporters: block transport, alter compounds and produce abnormal, new products.

Relevance of Drug Concentration

One mole contains 6 x 10²³ particles.
A 1 molar solution contains 1 mole in 1 liter.
Molecular Weight (MW) × Molarity (M) = Grams per Liter
- Example: Acetylcholine (ACh) has a molecular weight (MWt) of 146.21 which translates to 146.2 g/L in a 1 molar solution.

Drug-Receptor Interactions (Detailed)

Most drugs bind reversibly to receptors.
Binding is governed by association and dissociation rates.
Binding obeys the law of mass action, being related to the concentrations of reactants and products.

Affinity, Efficacy, and Potency

Affinity: strength of drug binding to the receptor.
Efficacy: ability of a drug-bound receptor producing a response.
Agonist: possesses both affinity and efficacy.
A + R ↔ AR → AR* → Response. (A = drug, R = receptor; AR* = activated receptor complex)

Agonists and Antagonists

Agonists: bind to receptors and cause a response (affinity and efficacy).
Antagonists: bind to receptors but do not cause a response (affinity only). They block the effects of agonists.

Drug Concentration and Drug Response

Drug response is generally proportional to the number of receptor sites bound by the drug.
Target receptors exist in different tissues throughout the body.
- Bmax: maximum number of receptors.
- B50: concentration where 50% of receptors are bound.
- Kd: dissociation constant.
- Emax: maximum response.

Partial Agonists

Drugs often cannot produce a maximum effect, even at full receptor occupancy; these are partial agonists.
A partial agonist's EC₅₀ is equal to its K_d , the dissociation constant.
The potency is dependent on both affinity and efficacy

Spare Receptors

Spare receptors are unoccupied receptors when the agonist achieves its maximum effect (E_max).
It is a concept reversed for partial agonists since submaximal effect is achieved at Bmax.
Clinical implications include hormone and energy economy and maintained drug efficacy.

Antagonism

There are three major types of antagonism:
- Reversible competitive.
- Irreversible competitive.
- Non-competitive.
The IC₅₀ is the concentration of an antagonist required to cause 50% inhibition.

Effects of Varying [Antagonist]

Increasing the concentration of antagonist leads to greater inhibition of the agonist's effects.

Reversible Competitive Antagonism

This is the most common type of antagonism in therapeutics.
It relies on a dynamic equilibrium between ligands and receptors.
High agonist concentrations can overcome the effect of the antagonist.

Other Types of Antagonism

Irreversible competitive: Antagonist dissociates slowly or not at all. Higher antagonist concentrations can suppress overall maximal response.
Non-competitive: Antagonist binds to a different site from the agonist, affecting its efficacy

Potency Comparisons

The potency of two drugs can be compared using their EC₅₀ values; smaller EC₅₀=more potent drug.
The maximum response values are also a relevant aspect to consider when evaluating drugs.

Studying That Suits You

Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

Description

This quiz focuses on drug-receptor interactions crucial for clinical practice. It covers the quantitative relationship between drug concentration and response, along with key pharmacological terms such as affinity, efficacy, and potency. Test your knowledge on how drugs interact with their targets and the fundamentals of pharmaceutics, pharmacodynamics, and pharmacokinetics.