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Questions and Answers
What does potency refer to in pharmacodynamics?
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?
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?
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)?
What is the formula for calculating the therapeutic index (TI)?
Which of the following is true about drugs with a narrow therapeutic index?
Which of the following is true about drugs with a narrow therapeutic index?
Which of the following drugs is an example of one that has a low therapeutic index?
Which of the following drugs is an example of one that has a low therapeutic index?
What effect does an increased dose have once the maximal efficacy is reached?
What effect does an increased dose have once the maximal efficacy is reached?
What is the main side effect that should be monitored when administering warfarin?
What is the main side effect that should be monitored when administering warfarin?
What is the primary effect of diphenhydramine?
What is the primary effect of diphenhydramine?
Which route of administration is considered to have a rapid effect of a drug?
Which route of administration is considered to have a rapid effect of a drug?
What type of drug effect occurs when two medications enhance each other's effects, leading to a combined effect greater than their individual effects?
What type of drug effect occurs when two medications enhance each other's effects, leading to a combined effect greater than their individual effects?
Which type of drug effect results in one drug inhibiting the effect of another?
Which type of drug effect results in one drug inhibiting the effect of another?
Which classification of drug effect involves replacing essential body compounds?
Which classification of drug effect involves replacing essential body compounds?
What are side effects usually a result of?
What are side effects usually a result of?
What is the example of potentiation given in the content?
What is the example of potentiation given in the content?
Which effect refers to the irritation of the inner wall of the colon to increase defecation?
Which effect refers to the irritation of the inner wall of the colon to increase defecation?
What does a higher INR indicate for a patient taking warfarin?
What does a higher INR indicate for a patient taking warfarin?
How is the peak level of a drug defined?
How is the peak level of a drug defined?
When should blood be drawn to assess trough levels of a medication?
When should blood be drawn to assess trough levels of a medication?
What is the onset of a drug?
What is the onset of a drug?
Which of the following is NOT a commonly monitored drug?
Which of the following is NOT a commonly monitored drug?
What does the duration of action of a drug refer to?
What does the duration of action of a drug refer to?
For which of the following routes of administration should blood be drawn to assess peak levels 30-60 minutes post-administration?
For which of the following routes of administration should blood be drawn to assess peak levels 30-60 minutes post-administration?
What is the purpose of measuring peak and trough drug levels?
What is the purpose of measuring peak and trough drug levels?
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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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