The fraction of an administered dose of unchanged drug that reaches the systemic circulation and is available to produce its effect.
Crucial for determining the appropriate oral dose compared to an intravenous dose for the same therapeutic effect.
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First-pass effect
Answer
The metabolism of a drug by the liver or gut wall enzymes before it reaches the systemic circulation, significantly reducing its bioavailability.
High first-pass metabolism often necessitates higher oral doses or alternative administration routes like IV or sublingual.
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Volume of Distribution (Vd)
Answer
The apparent volume into which a drug distributes in the body, reflecting the relationship between the amount of drug in the body and its concentration in the plasma.
A large Vd suggests extensive distribution into tissues, potentially requiring a higher loading dose to achieve target plasma concentrations.
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Clearance (CL)
Answer
The rate at which a drug is removed from the body, typically expressed as the volume of plasma cleared of drug per unit of time.
Essential for determining the maintenance dose and dosing interval to prevent drug accumulation or subtherapeutic levels.
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Half-life (t1/2)
Answer
The time required for the concentration of a drug in the plasma to decrease by 50% after absorption and distribution are complete.
Determines the time it takes to reach steady state and how quickly drug levels fall after discontinuation.
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Steady State
Answer
The point in drug administration where the rate of drug administration equals the rate of drug elimination, resulting in stable plasma drug concentrations.
Reached after approximately 4-5 half-lives of regular dosing, ensuring consistent drug concentration for optimal effect.
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Loading Dose
Answer
An initial higher dose of a drug given to rapidly achieve the desired target plasma concentration within the therapeutic range.
Used for drugs with long half-lives or when rapid therapeutic effects are needed, such as in acute emergencies.
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Maintenance Dose
Answer
The dose of drug required to sustain the desired steady-state plasma concentration within the therapeutic window over time.
Calculated to replace the amount of drug eliminated from the body between doses, keeping concentrations within the therapeutic window.
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Drug Protein Binding
Answer
The reversible association of a drug with plasma proteins (e.g., albumin), which limits the amount of free, pharmacologically active drug available.
Highly protein-bound drugs have less free drug available to exert effects, and displacement by other drugs can lead to toxicity.
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P-glycoprotein (P-gp)
Answer
An efflux transporter protein found in various tissues (e.g., gut, blood-brain barrier, kidney) that pumps many drugs out of cells, influencing drug absorption, distribution, and elimination.
Inhibiting P-gp can increase drug absorption and reduce elimination, potentially leading to higher drug levels and toxicity.
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Agonist
Answer
A drug that binds to a receptor and produces a maximal biological response, mimicking the effect of an endogenous ligand.
A full agonist produces the maximum possible effect, like a key perfectly fitting and turning a lock.
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Antagonist
Answer
A drug that binds to a receptor but produces no direct effect, instead blocking the action of an agonist or endogenous ligand.
Antagonists block the receptor without activating it, like a key that fits the lock but cannot turn it.
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Partial Agonist
Answer
A drug that binds to a receptor and produces a submaximal response, even when all receptors are occupied, never achieving the full effect of a full agonist.
Even at maximal receptor occupancy, a partial agonist will not elicit the same maximal response as a full agonist, useful for avoiding excessive stimulation.
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Therapeutic Index (TI)
Answer
A ratio comparing the dose that causes toxicity (TD50) to the dose that causes a therapeutic effect (ED50), indicating a drug's safety margin.
A narrow TI means a small difference between therapeutic and toxic doses, requiring careful monitoring to prevent adverse effects.
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Potency
Answer
The amount of drug needed to produce a given effect, often expressed as EC50 or ED50, which is the concentration or dose at which 50% of the maximal effect is achieved.
A drug with higher potency requires a smaller dose to achieve the same effect compared to a less potent drug.
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Efficacy
Answer
The maximal effect a drug can produce, regardless of dose, reflecting its intrinsic ability to elicit a response.
Efficacy is more clinically important than potency; a drug with higher efficacy can produce a greater maximal effect.
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Prodrug
Answer
An inactive compound that is metabolized in the body into an active pharmacological agent.
Prodrugs often improve drug absorption, reduce side effects, or prolong duration of action by becoming active only after metabolism.
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NSAIDs (Nonsteroidal Anti-inflammatory Drugs)
Answer
A class of drugs that inhibit cyclooxygenase (COX) enzymes, thereby reducing the synthesis of prostaglandins to relieve pain, inflammation, and fever.
Common side effects include gastrointestinal irritation and renal impairment due to their non-selective COX inhibition.
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Beta-blockers
Answer
Drugs that competitively antagonize beta-adrenergic receptors, primarily used to reduce heart rate, contractility, and blood pressure.
Contraindicated in conditions like severe bradycardia or acute decompensated heart failure due to their cardiac depressant effects.
Drugs that block the conversion of angiotensin I to angiotensin II, leading to vasodilation, reduced blood pressure, and decreased aldosterone secretion.
A common side effect is a dry cough, due to the accumulation of bradykinin, which is normally broken down by ACE.
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Opioids
Answer
Drugs that bind to opioid receptors (mu, kappa, delta) in the central nervous system and other tissues, producing analgesia, sedation, and euphoria.
Significant side effects include respiratory depression and constipation, requiring careful patient monitoring and management.
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Adverse Drug Reaction (ADR)
Answer
Any unintended, undesirable, and harmful reaction to a drug administered at a normal dose for prophylaxis, diagnosis, or therapy.
Distinguishes from side effects by being harmful and unintended, whereas side effects may be expected or tolerable.
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Idiosyncratic Reaction
Answer
A type B adverse drug reaction that occurs rarely and unpredictably in susceptible individuals, unrelated to the drug's known pharmacological effects or dose.
These unpredictable reactions are often genetically determined and are not dose-dependent, making them difficult to foresee.
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Teratogenicity
Answer
The capacity of a drug to cause developmental abnormalities or birth defects in a fetus when administered during pregnancy.
Pregnant women should avoid teratogenic drugs, as exemplified by thalidomide, which caused severe limb malformations.
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Absolute Contraindication
Answer
A condition or factor that makes the administration of a drug completely forbidden due to a high risk of severe adverse effects.
An example is giving epinephrine to a patient with pheochromocytoma, which can cause a life-threatening hypertensive crisis.
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Drug-Drug Interaction
Answer
A modification of the effect of one drug by the prior or concomitant administration of another drug, leading to altered efficacy or toxicity.
Can lead to increased toxicity or reduced efficacy, such as when warfarin's anticoagulant effect is enhanced by NSAIDs, increasing bleeding risk.
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Black Box Warning
Answer
The strongest warning that the FDA requires to be placed on a drug's label when there is reasonable evidence of an association of a serious hazard with the drug.
It alerts prescribers and patients to potentially fatal, life-threatening, or disabling adverse effects that may occur.
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Dose
Answer
The specific amount of medication administered to a patient at one time, often expressed in units of mass (e.g., mg) or volume (e.g., mL).
Accurate dose calculations ensure the correct amount of medication is given, whether in milligrams, units, or milliliters, to achieve therapeutic effects safely.
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Infusion Rate
Answer
The speed at which a medication is delivered intravenously, typically measured in milliliters per hour (mL/hour) or drops per minute (gtts/min).
Accurate calculation prevents too rapid or too slow administration, which could lead to toxicity or subtherapeutic levels.