Pharmacology: Drug Receptors, Effects, and Dose-Response Relationships

Who are the pioneers of modern pharmacology?

Paul Ehrlich, John Newport Langley, Alfred Joseph Clark

What does pharmacokinetics (PK) refer to?

Drug action

What does pharmacodynamics (PD) refer to?

Drug effect

What is a drug receptor?

The molecular component of a cell with which the drug interacts.

Where are drug receptors typically located?

Typically on the cell surface, embedded in the cell membrane.

What are the two main methods to study drug receptors?

1. Isolate and purify macromolecular components; 2. Determine amino acid sequence and express receptors in cultured cells.

What types of binding can drugs have with receptors?

1. van der Waals attraction; 2. Hydrogen bond; 3. Hydrophobic interaction; 4. Ionic bond; 5. Covalent bond.

What is an example of a covalent inhibitor?

Afatinib, a growth factor receptor (EGFR) covalent inhibitor.

What is an example of a dopamine D3 receptor antagonist?

Eticlopride, an antipsychotic analogue.

What are the physical characteristics of drugs?

1. Physical nature (solid, liquid, pH, hydrophilicity, hydrophobicity); 2. Size (typically MW 100-1000); 3. Shape (stereoisomerism).

What is an agonist?

A drug that causes a specific physiological effect due to direct interaction with a receptor.

What is an antagonist?

A compound that blocks the action of a specific agonist or endogenous substance without having intrinsic pharmacological activity.

What is an allosteric modulator?

A drug that binds to a different site on the receptor than that bound by endogenous ligands, modulating the effect positively or negatively.

What is the definition of addition in drug effects?

When two agonists producing the same effect are administered together, they produce an effect equal to the sum of their individual effects.

What is synergism in drug effects?

When two agonists administered together produce an effect greater than the sum of their individual effects.

What is potentiation in drug effects?

When a drug has no effect on its own but increases the effect of a second drug when administered together.

What is the molecular weight (MW) of Aspirin?

180.2

What is the molecular weight (MW) of Cyclosporin?

1202.6

What is the significance of structure-activity relationships (SAR) in pharmacology?

SAR studies help infer information from the kinetics of drug-receptor interactions.

What is the role of radio-ligand binding assays?

To study the binding interactions between drugs and receptors.

What is the importance of drug shape in pharmacology?

Drug shape, including stereoisomerism, can significantly affect receptor interaction and drug efficacy.

What is the difference between agonists and antagonists?

Agonists activate receptors to produce effects, while antagonists block receptor activation.

What is the role of hydrophobic interactions in drug-receptor binding?

Hydrophobic interactions help stabilize the binding of drugs to their receptors.

What is a common method for studying receptor function?

Cloning and expressing the receptor in cultured cells to study its function in a controlled environment.

What is the function of the receptor site concept?

It provides a logical explanation for the pharmacological effects of drugs.

What is potentiation in pharmacology?

When a drug is without effect on its own but increases the effect of a second drug when administered together.

What do quantal dose-response curves relate?

They relate drug dose to the frequency of drug-induced 'all-or-none' pharmacological effects.

What type of distribution is produced by plotting response frequency vs. dose in quantal dose-response curves?

A normal distribution.

Give an example of an all-or-none pharmacological effect.

The dose of barbiturate required to induce sleep.

What is the significance of re-plotting a dose-response curve in terms of percentage of subjects responding?

It yields a sigmoid (S-shaped) curve.

What is the difference between a linear plot and a semi-log plot in drug dose-response relationships?

A linear plot uses intuitive scaling, while a semi-log plot uses compact scaling.

What is tolerance in pharmacology?

When repeated administration of a given dose of a drug produces a decreased effect, requiring larger doses for the same effect.

Define tachyphylaxis.

A very rapidly developing tolerance; decreasing effect of a drug following consecutive doses given at short intervals.

What is desensitization in the context of drug receptors?

A reduced state of pharmacological responsiveness of a receptor due to continuous presence of the agonist.

What does the therapeutic index (TI) measure?

It measures drug effectiveness and safety, calculated as the ratio of LD50 to ED50.

What is ED50?

The smallest dose of a drug which is effective in 50% of individuals receiving the drug.

What is LD50?

The smallest dose of a drug which is lethal in 50% of individuals receiving the drug.

What is the margin of safety in pharmacology?

It relates the lethal dose in 0.1% of subjects to the effective dose in 99.9% of subjects.

What factors determine receptor occupancy?

Drug dose or availability at receptors and the affinity of the receptor for the drug.

How is the magnitude of drug effects related to receptor occupancy?

It is proportional to the number of receptors occupied by the agonist.

What are the kinetics of drug-receptor interactions similar to?

They are similar to classical Michaelis-Menten enzyme kinetics.

What is the role of the 'receptive substance' idea in pharmacology?

It was proposed by Paul Ehrlich and relates to drug interactions with receptors.

What is an agonist in pharmacology?

A substance that activates a receptor to produce a biological response.

What is synergism in pharmacology?

When two drugs work together to produce a greater effect than the sum of their individual effects.

What does the term 'addition' refer to in pharmacology?

The combined effect of two drugs that is equal to the sum of their individual effects.

What is the significance of receptor location in pharmacology?

It affects how drugs interact with receptors and the resulting pharmacological effects.

What is the concept of drug receptors?

Molecular targets for drugs that mediate their effects in the body.

What is the relationship between drug dose and pharmacological effect?

Higher doses generally lead to greater pharmacological effects, up to a certain limit.

What does the term 'drug-receptor binding kinetics' refer to?

The study of how drugs bind to receptors and the dynamics of these interactions.

What does KD represent in drug-receptor binding kinetics?

KD is the equilibrium dissociation constant, indicating the affinity of the receptor for the drug.

At what point is KD equal to the concentration of the drug?

KD is equal to the concentration of the drug when 50% of the receptors are occupied.

What is the relationship between drug effects and receptor occupancy?

The magnitude of drug effects is proportional to the number of receptors occupied by the agonist.

What happens when KD for a drug is small?

When KD is small, the drug has a high affinity for the receptor.

What happens when KD for a drug is large?

When KD is large, the drug has a low affinity for the receptor.

What is intrinsic activity or efficacy in pharmacology?

Intrinsic activity or efficacy is the degree of effect obtainable for a given level of receptor occupancy.

How is potency defined in pharmacology?

Potency is the comparison of doses of two or more drugs required to produce the same effect.

What is a neutral antagonist?

A neutral antagonist has affinity for the receptor but does not have intrinsic activity (efficacy).

What defines competitive, reversible antagonism?

In competitive antagonism, the agonist and antagonist compete for the same receptors, and the effect is proportional to the amount of agonist present.

What occurs during irreversible antagonism?

In irreversible antagonism, the antagonist binds permanently to the receptor, decreasing the number of receptors available for the agonist.

What is non-competitive (allosteric) antagonism?

In non-competitive antagonism, the antagonist binds to a different site on the receptor, preventing the agonist from producing an effect.

What is positive allosteric modulation?

Positive allosteric modulation typically results in a leftward and upward shift in the dose-response curve, enhancing the effect of the agonist.

What is the difference between synergism and potentiation?

Synergism occurs when two agonists produce an effect greater than the sum of their individual effects, while potentiation occurs when a drug without effect increases the effect of another drug.

What is tachyphylaxis?

Tachyphylaxis is a rapid decrease in response to a drug after repeated doses.

What is desensitization in pharmacology?

Desensitization is a mechanism where prolonged exposure to an agonist decreases the receptor's responsiveness.

What is the therapeutic index?

The therapeutic index is the ratio of the dose that produces toxicity to the dose that produces a therapeutic effect (ED50 and LD50).

What does the slope of a dose-response curve indicate?

The slope indicates the range of response during the ascending phase of the curve.

What is the significance of EC50 in pharmacology?

EC50 is the concentration of a drug that produces 50% of its maximum effect.

What does the term 'agonist' refer to?

An agonist is a substance that activates a receptor to produce a biological response.

What is the role of ligand occupancy?

Ligand occupancy leads to the activation of the receptor and a functional response.

What does a log dose-response curve illustrate?

A log dose-response curve illustrates the relationship between the concentration of a drug and the magnitude of its effect.

What is the effect of a positive allosteric modulator on an agonist?

A positive allosteric modulator enhances the effect of an agonist without activating the receptor itself.

What is the difference between a competitive antagonist and a non-competitive antagonist?

A competitive antagonist competes with the agonist for the same binding site, while a non-competitive antagonist binds to a different site, altering receptor function.

What is the relationship between drug concentration and receptor-bound drug?

The relationship describes how drug concentration affects the amount of drug bound to receptors and the resulting biological effect.