Pharmacology Chapter on Antagonism and Selectivity

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Questions and Answers

What term is used to describe drugs that stabilize receptors in an inactive conformation?

Inverse agonists (correct)

Chemical antagonists

Functional antagonists

Partial agonists

How do partial agonists behave in the presence of a full agonist?

As selective agonists

As competitive antagonists (correct)

As inverse agonists

As complete agonists

What factor primarily influences the affinity of a drug for its receptor?

The drug's dosing schedule

The route of administration

The drug's chemical structure (correct)

The patient's age

Which drug is known for its low specificity due to interaction with multiple receptors?

Amiodarone Signup and view all the answers

What is the primary outcome of a drug having high specificity?

Limited interactions with receptors Signup and view all the answers

What characteristic of drugs can lead to adverse side effects due to off-target interactions?

Broad specificity Signup and view all the answers

What defines the intrinsic activity of a drug?

The efficacy with which it activates its receptor Signup and view all the answers

Which property of a drug's stereoisomers can vary, affecting its pharmacodynamics?

Pharmacokinetic properties Signup and view all the answers

What does the therapeutic index of a drug primarily indicate?

The difference between the minimum effective dose and the minimum toxic dose. Signup and view all the answers

Why is monitoring of clinical and surrogate markers crucial when using the population therapeutic window?

To adapt the dosage based on individual patient responses for optimal therapy. Signup and view all the answers

In clinical pharmacology, which statement best describes the role of the route of administration?

Different routes can alter the speed and intensity of drug response significantly. Signup and view all the answers

What is a potential consequence of overlapping concentrations required for therapeutic and toxic effects?

The need for careful dose management to avoid toxicity. Signup and view all the answers

Which of the following is true regarding the effects of magnesium sulfate when administered via different routes?

Topical administration can help reduce swelling in joints. Signup and view all the answers

What effect does the combination of drugs A and B demonstrate if the efficacy is greater than the sum of their individual effects?

Positive synergism Signup and view all the answers

Which statement correctly describes a characteristic of antagonists?

They bind without exerting effect. Signup and view all the answers

How is the therapeutic index represented in pharmacodynamics?

LD50/ED50 ratio Signup and view all the answers

What does a quantal concentration-effect curve analyze?

The median effective dose in a population Signup and view all the answers

What describes the condition where the combination of drugs has less efficacy than expected based on their individual effects?

Negative synergism Signup and view all the answers

Which factor is NOT typically associated with variability in individual drug responsiveness?

Time of day Signup and view all the answers

What happens to the required concentrations of drugs A and B if they exhibit positive synergism?

They decrease below additive levels. Signup and view all the answers

What can influence the dynamic nature of drug receptors?

Endogenous and exogenous factors Signup and view all the answers

What is the primary concern regarding the maintenance treatment of heart failure with digoxin in women compared to men?

It is associated with higher mortality in women. Signup and view all the answers

Which of the following environmental factors is known to influence drug metabolism?

Consumption of charcoal broiled meat Signup and view all the answers

What type of tolerance refers to the requirement of higher doses of a drug to achieve the same effect?

Acquired tolerance Signup and view all the answers

Which statement best describes tachyphylaxis?

It is a form of rapid tolerance development. Signup and view all the answers

Which of the following drugs is NOT associated with side effects of gynaecomastia or loss of libido in men?

Amlodipine Signup and view all the answers

What is the main reason that the L-enantiomer of sotalol is considered more potent than the D-enantiomer?

The L-enantiomer has a higher affinity for β adrenergic receptors. Signup and view all the answers

What phenomenon occurs with chronic administration of nitro-vasodilators that can impact treatment efficacy?

Tachyphylaxis. Signup and view all the answers

Which of the following describes a characteristic of drug potency?

It involves comparison of drug EC50 values. Signup and view all the answers

What does efficacy refer to in the context of drug-receptor interactions?

The ability of a drug to activate a receptor and generate a response. Signup and view all the answers

Which of the following accurately describes a non-receptor interacting mechanism of drug action?

Aluminum and magnesium hydroxides neutralize gastric acid chemically. Signup and view all the answers

Which principle is the basis of receptor occupancy theory in pharmacology?

Drug effects are proportional to the number of receptors occupied. Signup and view all the answers

Which characteristic defines a partial agonist in pharmacology?

It elicits a full response only at specific concentrations. Signup and view all the answers

What effect does chronic drug administration commonly have on drug receptors?

Receptor desensitization. Signup and view all the answers

Study Notes

Antagonism

Antagonism is the inhibition of the action of a drug by another drug.
Antagonism can happen in different ways including competitive antagonism, combining with the agonist, or through functional antagonism
Partial agonists only partially activate receptors.
Inverse agonists stabilize receptors in an inactive conformation, decreasing their activity.

Drug Selectivity

The strength of the interaction between a drug and its receptor is called affinity.
Affinity, along with the intrinsic activity of a drug, is determined by its chemical structure.
Drugs interacting with a single type of receptor expressed on limited cells exhibit high specificity.
Drugs acting on ubiquitously-expressed receptors have widespread effects.
Many drugs exhibit broad (low) specificity, interacting with multiple receptors. This can enhance clinical utility but also lead to adverse effects from "off-target" interactions.
Amiodarone, used to treat cardiac arrhythmias, exhibits broad specificity, interacting with various receptors and causing toxicities.
Stereoisomers of a drug can exhibit different pharmacodynamic and pharmacokinetic properties.

Chronic Drug Administration

Chronic drug administration can cause downregulation of receptors or desensitization, requiring dose adjustments for effective therapy.
Tachyphylaxis is the rapid development of tolerance to a drug after repeated administration.

Non-receptor Mechanisms

Some drug effects are not mediated by receptors.
Aluminum and magnesium hydroxides act chemically to neutralize gastric acid.
Mannitol acts osmotically to change water distribution, affecting diuresis, catharsis, circulating volume, and cerebral edema.

Receptor Occupancy Theory

This theory proposes that drug effects arise from the occupation of receptors by the drug, based on the law of mass action.
Dose-response curves illustrate the relationship between drug concentration and observed effects.

Affinity, Efficacy, and Potency

Drug-receptor interactions involve binding and generation of a response, with affinity being the measure of the reversible formation of the ligand-receptor complex.
Potency refers to the relative dose required to achieve a certain effect, with a more potent drug having a lower EC50.
Efficacy reflects the capacity of a drug to activate a receptor and produce a cellular response.
Full agonists elicit a full response at some concentration.
Partial agonists do not elicit a full response, even at high doses.
Antagonists bind to a receptor without producing a response.

Additivity and Synergism

Combinations of drugs can achieve additive or synergistic effects.
Positive synergism results in superadditive effects, allowing reduced concentrations of each drug.
Negative synergism (subadditive effects) occur when the combined efficacy is less than expected, requiring higher drug concentrations.

Variability in Individual and Population Pharmacodynamics

Individuals vary in their response to drugs, and the response can change due to disease, age, and prior drug administration.
Receptor concentrations and functions can be altered by both endogenous and exogenous factors.

Population Variability

Population pharmacodynamic variability influences the interpretation of data on drug levels with efficacy and toxicity.

Quantal Concentration-Effect Curve

This curve provides a population-based analysis of pharmacodynamic response, plotting the percentage of individuals experiencing an effect at different drug concentrations.
The median effective dose (ED50) is the dose producing a specified effect in 50% of the population.

Therapeutic Index and Therapeutic Window

The therapeutic index (LD50/ED50 ratio) reflects drug selectivity in producing desired effects versus adverse effects.
The therapeutic window represents the range of drug concentrations providing therapeutic efficacy with minimal toxicity.
In clinical studies, the therapeutic index evaluates the overlap between concentrations required for therapeutic effects and toxic effects in the population.
The population therapeutic window, though useful, should be combined with clinical markers for accurate dosage adjustments.

Factors Modifying Drug Action

Numerous factors influence drug response variability, including:

Route of Administration

Parenteral administration provides more rapid, pronounced, and predictable effects compared to oral administration.
Different routes of administration can lead to different drug uses: magnesium sulfate demonstrates distinct effects when administered orally, topically, or intravenously.

Direct Administration

Direct drug application to tissues achieves localized effects on the skin, mucous membranes, and respiratory tract through aerosol sprays.

Sex

Sex-specific responses to drugs can occur, with some drugs exhibiting different effects in males and females.

Environmental Factors

Environmental factors, like exposure to insecticides and tobacco smoke, can alter drug metabolism and responses.

Diet

Diet type can influence drug absorption.

Tolerance

Tolerance requires higher doses of a drug to achieve a therapeutic response.
Tolerance can be natural, acquired, or cross-tolerance (between drugs like alcohol and barbiturates).
Pharmacokinetic tolerance involves altered drug disposition, while pharmacodynamic tolerance involves cellular changes.
Tachyphylaxis is rapid tolerance development with repeated doses.

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Description

This quiz covers key concepts in pharmacology, focusing on antagonism and drug selectivity. It explores various mechanisms of antagonism, such as competitive and functional antagonism, and the significance of drug affinity and specificity. Test your understanding of how these factors influence drug interactions and clinical outcomes.