Pharmacodynamics: Potency, Efficacy, and Safety

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Questions and Answers

What does potency refer to in pharmacodynamics?

The average dosage of a drug used in therapy

The amount of drug needed to elicit a specific response (correct)

The maximum effect a drug can produce

The safety margin between therapeutic and toxic doses

What does a high therapeutic index indicate about a drug?

The drug requires regular blood monitoring

The drug has a low risk of toxicity (correct)

The drug has a high risk of toxicity

The drug is ineffective at common doses

Which statement about efficacy is correct?

Efficacy is synonymous with drug potency

Efficacy measures the maximum effect obtainable from a drug (correct)

Efficacy only considers side effects of the drug

Efficacy refers to how much drug is needed for an effect

What is the formula for calculating the therapeutic index (TI)?

TI = TD50 / ED50 Signup and view all the answers

Which of the following is true about drugs with a narrow therapeutic index?

They require close monitoring for patient safety Signup and view all the answers

Which of the following drugs is an example of one that has a low therapeutic index?

Warfarin Signup and view all the answers

What effect does an increased dose have once the maximal efficacy is reached?

Has no further effect Signup and view all the answers

What is the main side effect that should be monitored when administering warfarin?

Bleeding Signup and view all the answers

What is the primary effect of diphenhydramine?

Antihistamine Signup and view all the answers

Which route of administration is considered to have a rapid effect of a drug?

Inhalations Signup and view all the answers

What type of drug effect occurs when two medications enhance each other's effects, leading to a combined effect greater than their individual effects?

Synergistic Signup and view all the answers

Which type of drug effect results in one drug inhibiting the effect of another?

Antagonistic Signup and view all the answers

Which classification of drug effect involves replacing essential body compounds?

Replacement Signup and view all the answers

What are side effects usually a result of?

The drug's lack of specificity within the therapeutic range Signup and view all the answers

What is the example of potentiation given in the content?

Alcohol and aspirin Signup and view all the answers

Which effect refers to the irritation of the inner wall of the colon to increase defecation?

Irritation Signup and view all the answers

What does a higher INR indicate for a patient taking warfarin?

Longer time for blood to clot Signup and view all the answers

How is the peak level of a drug defined?

When the drug reaches its highest concentration in the blood Signup and view all the answers

When should blood be drawn to assess trough levels of a medication?

Immediately before the next dose Signup and view all the answers

What is the onset of a drug?

The time it takes for the drug to begin exerting a therapeutic effect Signup and view all the answers

Which of the following is NOT a commonly monitored drug?

Ibuprofen Signup and view all the answers

What does the duration of action of a drug refer to?

The length of time the drug produces its therapeutic effect Signup and view all the answers

For which of the following routes of administration should blood be drawn to assess peak levels 30-60 minutes post-administration?

Intramuscular Signup and view all the answers

What is the purpose of measuring peak and trough drug levels?

To check if drug concentration is in a toxic range or requires dosage adjustment Signup and view all the answers

Study Notes

Pharmacodynamic Phase

Focuses on how drugs affect the body and the physiological responses to drug concentration changes at the site of action.
Evaluates drug actions via two main metrics: potency and efficacy.

Potency and Efficacy

Potency: Refers to the amount of drug required to elicit a specific physiological effect (e.g., pain relief).
Efficacy: Indicates the maximum effect a drug can achieve (e.g., reducing blood pressure).
Maximal Efficacy (Emax): The highest effect achievable by a drug; beyond this point, increasing dosage won't enhance effects.

Therapeutic Index

Defines drug safety by comparing toxic dose and therapeutic dose.
Calculated as TI = TD50/ED50:
- TD50: Dose causing toxicity in 50% of the population.
- ED50: Dose producing a therapeutic effect in 50% of the population.
A narrow therapeutic index indicates closer values for TD50 and ED50, requiring careful monitoring to ensure safety.
A higher therapeutic index signifies a safer drug, while a lower therapeutic index indicates heightened risk.

Clinical Implications

Therapeutic index allows for anticipated drug effects, guiding clinicians and aiding safe prescribing.
Commonly monitored drugs with a narrow therapeutic index include warfarin, lithium, digoxin, phenytoin, and gentamicin.

Warfarin

An anticoagulant drug used to decrease blood clotting; indicated for heart attacks and strokes.
Major side effect includes bleeding; requires monitoring of INR (International Normalized Ratio).
Normal INR range for patients on warfarin is between 2 to 3; higher INR increases bleeding risk.

Drug Action Timing

Onset: Time to reach minimum effective concentration after administration.
Peak: Highest concentration of the drug in the blood.
Duration of Action: Period during which the drug produces its therapeutic effect.

Drug Concentration Measurement

Peak and trough drug levels are essential for assessing drug concentrations and avoiding toxicity.
Peak: Measured at specific times post-administration depending on the route (e.g., IV, oral).
Trough: Drawn before the next dose to ensure levels are safe and effective.

Types of Drug Responses

Primary Effects: Generally desirable physiological responses.
Secondary Effects: May be desirable or undesirable (e.g., drowsiness from antihistamines).

Drug Action Types

Stimulation: Increases cell activity (e.g., T3/T4 for hypothyroidism).
Depression: Decreases organ function (e.g., iodine).
Replacement: Supplies essential compounds (e.g., insulin).
Inhibition/Killing: Targets harmful organisms (e.g., antibiotics).
Irritation: Induces increased bodily functions (e.g., laxatives).

Drug Interaction Effects

Additive Effect: Combining similar acting drugs enhances effects (e.g., ibuprofen + paracetamol).
Synergistic Effect: Combined effect exceeds the sum of individual effects (e.g., aspirin + codeine).
Potentiation: A drug with no effect amplifies another (e.g., alcohol with aspirin).
Antagonistic Effect: One drug reduces the effect of another (e.g., tetracycline + antacid).

Side Effects and Allergic Reactions

Side Effects: Arise from the drug's pharmacologic action, often due to a lack of specificity within therapeutic ranges.
Allergic Reactions: Occur when the immune system responds unpredictably to a drug, sometimes referred to as sensitization.

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Description

Explore the pharmacodynamic phase, focusing on how drugs impact the body and their physiological responses. This quiz covers key concepts like potency, efficacy, and the therapeutic index, evaluating drug actions and safety profiles. Test your knowledge of these important pharmacological principles.