Pharmacology: Factors Affecting Drug Response

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Questions and Answers

How does the body size of a patient influence the plasma concentration of a drug?

A larger body size results in a lower plasma concentration for a given dose, leading to a reduced effect.

In what ways does age affect drug absorption, metabolism, and excretion?

Neonates and infants have underdeveloped metabolizing systems, while older patients may have degenerative changes that reduce their activities.

What impact do genetic factors have on drug metabolism?

Congenital deficiencies in metabolizing enzymes can significantly affect the plasma levels of drugs and their responses.

Explain how nutritional factors can affect drug response.

Severe malnutrition, particularly protein deficiency, can reduce enzyme activity, which is essential for drug metabolism. Signup and view all the answers

Why might drug doses be reduced for women compared to men?

Women generally have a higher percentage of body fat, affecting drug oxidation rates, which can lead to more pronounced drug effects. Signup and view all the answers

How do health conditions such as liver or kidney diseases affect drug response?

Patients with liver or kidney diseases exhibit altered drug metabolism and excretion, leading to different responses compared to healthy individuals. Signup and view all the answers

What significance does the time of drug administration hold in pharmacodynamics?

The timing can affect the drug's absorption and effectiveness, as physiological states may vary throughout the day. Signup and view all the answers

How can emotional status influence a patient's response to medication?

Emotional states can impact drug absorption and metabolism, potentially altering the intended therapeutic effect. Signup and view all the answers

How does daylight affect the action of stimulating drugs and hypnotics?

Daylight enhances the effects of stimulating drugs and diminishes the action of hypnotics. Signup and view all the answers

What impact can emotional status have on the efficacy of a placebo?

Emotional status can lead to considerable improvements in sleep, appetite, and well-being after a placebo is administered. Signup and view all the answers

Describe one method by which drug interactions can occur.

Drug interactions can occur through the acceleration or inhibition of drug metabolism. Signup and view all the answers

What is the basic principle behind drug-receptor interaction according to the drug-receptor theory?

The drug-receptor theory states that a drug must fit onto a specific receptor to produce its effect, similar to a key fitting a lock. Signup and view all the answers

Differentiate between an agonist and an antagonist in terms of receptor interaction.

An agonist has both affinity and efficacy, stimulating a receptor, while an antagonist has affinity but no efficacy, blocking receptor action. Signup and view all the answers

What role do enzymes play in the body's chemical reactions?

Enzymes function as substances that speed up many chemical reactions within the body. Signup and view all the answers

How does the administration of two drugs concurrently affect their therapeutic value?

Concurrent administration can influence the therapeutic values of each drug by interactions that may enhance or inhibit their effects. Signup and view all the answers

Explain how darkness influences the effectiveness of hypnotics.

Darkness serves as a sedative, making hypnotics more effective when administered at night. Signup and view all the answers

What is the definition of efficacy in pharmacology?

Efficacy is the ability of a drug to produce a physiological response upon interacting with a receptor. Signup and view all the answers

How does an agonist differ from an antagonist?

An agonist mimics the response of an endogenous ligand and produces a biological effect, while an antagonist decreases the actions of another drug or endogenous ligand without producing a response. Signup and view all the answers

What does EC50 represent in pharmacodynamics?

EC50 is the drug dose that results in fifty percent of the maximal response. Signup and view all the answers

What characterizes a full agonist?

A full agonist has a strong affinity for its receptor and produces a maximal biological response. Signup and view all the answers

Explain how competitive antagonism affects an agonist's dose-response curve.

Competitive antagonism shifts the agonist's dose-response curve to the right, indicating that a higher dose of the agonist is needed to achieve the same effect. Signup and view all the answers

What is functional antagonism in pharmacology?

Functional antagonism occurs when an antagonist acts at a different receptor to initiate effects that are opposite to those of the agonist. Signup and view all the answers

Describe the role of allosteric antagonism.

Allosteric antagonism involves an antagonist binding to a site other than the agonist's binding site, preventing receptor activation indirectly. Signup and view all the answers

What is a chemical antagonist?

A chemical antagonist inactivates another drug by combining with it and preventing its effect. Signup and view all the answers

How does food generally affect the absorption of drugs like fenoprofen, indomethacin, and isoniazid?

Food reduces the rate of absorption of these drugs. Signup and view all the answers

What is the effect of food on the absorption rate of ascorbic acid and metoclopramide?

Food increases the rate of absorption of both ascorbic acid and metoclopramide. Signup and view all the answers

What impact does the type of food have on drug absorption, particularly with fats and sugars?

Fats and sugars can reduce gastric emptying, thereby decreasing the rate and extent of absorption of certain drugs. Signup and view all the answers

What is the therapeutic index and why is it important?

The therapeutic index is the ratio of the minimum dose that produces toxicity to the minimum dose that produces a therapeutic response, indicating the safety of a drug. Signup and view all the answers

When is a drug considered toxic based on its therapeutic index?

A drug is considered toxic when its therapeutic index is 2 or less. Signup and view all the answers

What are idiosyncratic reactions in relation to drug effects?

Idiosyncratic reactions are genetically-determined abnormal reactivity to a drug. Signup and view all the answers

What are some possible delayed toxic effects of drugs, such as with Chloramphenicol?

Toxic effects like Chloramphenicol-induced aplastic anemia may occur weeks after administration. Signup and view all the answers

What type of effects can drugs produce aside from their primary therapeutic effect?

Drugs typically produce several effects, most of which are considered undesirable or side effects. Signup and view all the answers

What is the role of local anesthetics in nerve function?

Local anesthetics interfere with the movement of ions across the cell membrane, thereby preventing nerve function. Signup and view all the answers

How do antimetabolites affect cell division?

Antimetabolites resemble natural metabolites needed for cell function, preventing cells from using these metabolites and hindering division. Signup and view all the answers

What defines an agonist in pharmacology?

An agonist is an agent that binds to a receptor and elicits a biological response. Signup and view all the answers

Describe the relationship between drug concentration and pharmacologic response.

As the concentration of a drug increases, the magnitude of its pharmacologic effect also increases. Signup and view all the answers

What is EC50 and why is it significant?

EC50 is the drug dose that produces fifty percent of the maximum response, indicating the potency of the drug. Signup and view all the answers

How does the potency of drugs A and B differ when comparing their EC50 values?

Drug A, with a lower EC50, is more potent than Drug B because it requires a smaller amount to achieve fifty percent of the maximum effect. Signup and view all the answers

What shape characterizes the graph of a graded response curve?

The graph of a graded response curve is typically described as a rectangular hyperbola. Signup and view all the answers

Explain the significance of drug-receptor interactions in pharmacology.

Drug-receptor interactions determine the pharmacologic response and the effectiveness of a drug's action at a given concentration. Signup and view all the answers

What distinguishes a partial agonist from a full agonist regarding efficacy?

A partial agonist has efficacy greater than zero but less than that of a full agonist. Signup and view all the answers

How does the presence of a partial agonist affect the Emax of a full agonist?

As the concentration of the partial agonist increases, the Emax of the full agonist decreases until it reaches the Emax of the partial agonist. Signup and view all the answers

What is drug tolerance and what are its potential causes?

Drug tolerance is a decreased response to the usual dose of a drug after repeated administration, which can be caused by changes in receptors, exhaustion of mediators, increased metabolic degradation, or physiological adaptation. Signup and view all the answers

What defines psychological dependence on a drug?

Psychological dependence refers to the emotional and mental compulsion to use a drug, often seen in cases like tobacco smoking. Signup and view all the answers

In the context of drug-drug interactions, what is an additive effect?

An additive effect occurs when two drugs with similar effects produce a combined effect equal to the sum of their individual effects, i.e., 1+1=2. Signup and view all the answers

Explain the concept of potentiation in drug interactions.

Potentiation occurs when a drug with no effect enhances the effect of another active drug, resulting in an effect greater than the active drug alone, i.e., 0+1>1. Signup and view all the answers

What is meant by the term 'antagonism' in drug interactions?

Antagonism refers to the interaction of drugs with opposite effects given simultaneously, which can be chemical, physiological, or pharmacological. Signup and view all the answers

How can food interactions affect drug absorption?

The presence of food can alter the absorption of drugs from the gastrointestinal tract, potentially affecting their efficacy. Signup and view all the answers

Study Notes

Pharmacodynamics of Drugs

Pharmacodynamics is the study of the actions of drugs and their mechanisms of action.
This includes the pharmacological actions of drugs and the mechanisms by which those actions occur.

Drug Actions

Factors affecting drug action include:
- Patient size (body weight or surface area): Larger body size results in lower plasma drug concentration and lower effect for a given dose.
- Patient age: Drug response varies with age due to differences in absorption, metabolism, and excretion. Neonates and infants have undeveloped excretory and metabolizing systems, while older patients may have degenerative changes affecting these systems.
- Patient gender: Doses of potent drugs for women may need to be reduced slightly due to higher percentage of fatty tissue compared to men. Oxidation of drugs is slower in fatty tissue than in skeletal muscle; therefore, drug effects might be more pronounced in women. During lactation, some drugs may be excreted in breast milk, potentially affecting the infant.
- Genetic factors: Enzymes, mostly in the liver, break down drugs, ending their action. Congenital deficiencies in metabolizing enzymes can affect drug plasma levels and response.
- Nutritional factors: Metabolic enzymes are made of protein. Severe malnutrition can decrease enzyme activity due to protein deficiency, impacting drug response.
- Health conditions: Individuals with liver or kidney disease show different drug responses, often due to reduced drug metabolism and excretion.
- Time of administration: Daylight enhances the effect of "stimulating drugs," while diminishing the effect of hypnotics. Darkness is a sedative; hypnotics are most effective at night.
- Emotional status: A placebo can induce improvements in sleep, appetite, and well-being.
- Drug interactions: Concurrent drug administration can impact the therapeutic value of each drug in various ways. Mechanisms include changes in drug metabolism, plasma protein binding, gastrointestinal tract uptake, renal clearance, or interactions at the receptor level.

Mechanisms of Drug Actions

Drug-receptor interaction (receptor theory): Receptors are specific sites (inside or on the cell surface) that drugs bind to, mediating their actions. Drug fits into the receptor like a key into a lock (Key & Lock theory). Drugs can either stimulate (agonist) or occupy the receptor without action (antagonist).
Enzyme inhibitors: Drugs can inhibit enzyme activity, affecting chemical reactions in the body.
Action on cell membranes: Certain drugs, like local anesthetics, can affect ion movement across cell membranes, affecting nerve function.
Antimetabolites: Drugs similar in structure to endogenous metabolites can disrupt cellular functions by interfering with the use of endogenous metabolites. For example, some anticancer agents work this way.

Dose-Response Relationships

An agonist binds to a receptor and elicits a biological response. The magnitude of drug effect depends on drug concentration at the receptor site.
As drug concentration increases, the magnitude of the pharmacologic effect also increases. Drug response is continuous and gradual.
A graph of this relationship is a graded response curve.
This curve often resembles a rectangular hyperbola.
EC50 (Effective Concentration 50): The dose causing 50% of maximum response is useful in determining drug potency. The smaller the EC50, the more potent the drug.

Potency

Potency is a measure of the amount of drug necessary to produce an effect of a given magnitude.
Determined by the EC50 (the drug concentration needed to produce 50% of maximum effect).
A lower EC50 indicates higher potency.

Efficacy (Intrinsic Activity)

Efficacy is the ability of a drug to elicit a physiological response upon interacting with a receptor.
It's dependent on the number and efficacy of drug-receptor complexes formed.
Plotting the log of drug concentration creates sigmoid curves.

Drug Tolerance

Tolerance is a decreased response to a drug after repeated administration; a form of desensitization or tachyphylaxis.
Possible causes: changes or loss of receptors, mediator exhaustion, increased drug metabolism, or physiological adaptation by the body.

Drug Dependence

Drug dependence describes the individual's reliance on a certain drug. Drug cessation may induce withdrawal symptoms.
Two main types:
- Psychological dependence: Individual cravings or psychological need for the drug (e.g. tobacco smoking)
- Physical dependence: Body physically adapting to the presence of a drug. (e.g. morphine, alcohol, barbiturates)

Drug-Drug Interactions

When two drugs are administered together, they may exhibit:
- Additive effect: combined effect is equal to the sum of individual effects (1+1=2)
- Synergism: combined effect is greater than the sum of individual effects (1+1>2)
- Potentiation: a drug without effect enhances the effect of another drug (0+1>1)
- Antagonism (drugs of opposite effects are given simultaneously)

Drug-Food Interactions

Food may influence drug absorption in the gastrointestinal tract.
Some drugs' absorption is reduced by stomach food; others might absorb quicker (e.g., ascorbic acid).
The type of food can influence gastric emptying, impacting absorption rates (e.g., fats/sugars can reduce absorption).
Certain food components can interact with drugs, reducing absorption (e.g., calcium in dairy products and tetracycline).

Therapeutic Index and Margin of Safety

All drugs produce toxic responses at high doses.
The therapeutic index is the ratio of the dose producing toxicity to the dose producing the therapeutic response.
A higher ratio indicates higher safety of the drug.
The therapeutic index is also determined by the ratio of the dose that kills 50% of the animals, to the dose that produces 50% of the therapeutic effect in animals.

Unwanted Drug Effects

Adverse effects related to dosage: Most drugs have multiple effects, only one of which is the primary intended result. Unwanted secondary effects are called side-effects.
- Toxic effects: Pathological or genotoxic (DNA-altering). Toxicity incidence and severity depend on the drug concentration. These effects frequently occur shortly after administration, but some, like cancer, take longer to manifest (e.g., 20-30 years).
Adverse effects unrelated to dosage:
- Idiosyncratic reactions: Reactions are genetically determined and qualitatively similar between individuals but different in their intensity (sensitivity or insensitivity). For instance, a serious hemolytic anemia can develop in response to primaquine, especially in certain populations. Also, genetically-linked resistance to warfarin.
- Allergic reactions: A previous chemical exposure can trigger an allergic response towards structurally similar substances. Allergic reactions involve the immune system and can manifest in different ways (e.g., immediate hypersensitivity, delayed-type hypersensitivity).

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Description

Explore various factors influencing drug response in this pharmacology quiz. Delve into how body size, age, genetics, and nutritional aspects affect drug absorption, metabolism, and efficacy. Test your understanding of pharmacodynamics and the role of emotional status in medication response.