Pharmacology Drug Absorption and Metabolism Quiz

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Questions and Answers

What is the primary mechanism for the sustained delivery of nitroglycerin?

Inhalation route

Intravenous route

Oral route

Topical route (correct)

Which process involves the movement of a drug against a concentration gradient?

Carrier-mediated diffusion

Facilitated diffusion

Active transport (correct)

Passive diffusion

What primarily drives passive diffusion in drug absorption?

Energy from ATP

Concentration gradient (correct)

Carrier proteins

Membrane permeability

What form of a weak acid can permeate through membranes more readily?

Uncharged form HA Signup and view all the answers

Which factor influences the ratio between charged and uncharged drug forms?

pH at the absorption site Signup and view all the answers

What does a lower pKa value of a drug indicate?

Stronger acid strength Signup and view all the answers

What is the characteristic of weak bases in terms of protonation?

Protonation produces an uncharged form Signup and view all the answers

Which statement about ionization constant (pKa) is true?

Represents the ratio of protonated to nonprotonated forms at a specific pH Signup and view all the answers

How does an increased volume of distribution (Vd) affect the half-life of a drug?

It increases the half-life of the drug. Signup and view all the answers

What role do plasma proteins, such as albumin, play in drug action?

They sequester drugs and render them pharmacologically inactive. Signup and view all the answers

What is the primary site for drug metabolism in the body?

Liver Signup and view all the answers

Which chemical reaction is NOT considered a phase I metabolic process?

Conjugation Signup and view all the answers

What happens to most drugs in metabolic reactions?

They are converted to inactive metabolites. Signup and view all the answers

What is a pro-drug?

A drug that must be metabolized to become active. Signup and view all the answers

Which type of drug tends to have the strongest affinity for albumin?

Anionic drugs (weak acids) Signup and view all the answers

What is the effect of hypoalbuminemia on drug binding?

It decreases the level of free drug. Signup and view all the answers

What is a characteristic of subcutaneous (SC) injections?

They reduce risks associated with intravascular injections. Signup and view all the answers

Which drug administration method is used for local effects?

Topical Signup and view all the answers

What is the purpose of using epinephrine in subcutaneous injections?

To restrict the area of action of a drug. Signup and view all the answers

Which route of drug administration allows rapid absorption due to the large surface area of the lungs?

Inhalation Signup and view all the answers

What is an example of intradermal injection?

BCG vaccination Signup and view all the answers

What is the main use of intranasal drug administration?

For local drug effects in nasal passages. Signup and view all the answers

What is a primary feature of intrathecal drug administration?

It directly delivers drugs into the cerebrospinal fluid. Signup and view all the answers

What describes transdermal drug administration?

It achieves systemic effects through skin application. Signup and view all the answers

What is the primary focus of pharmacokinetics?

What the body does to the drug Signup and view all the answers

Which of the following best describes toxicology?

Study of harmful effects of drugs Signup and view all the answers

What does pharmacodynamics study?

The body’s response to drugs Signup and view all the answers

Which route of drug administration is considered the most common?

Oral Signup and view all the answers

What is pharmacogenomics concerned with?

Discovery of new drugs using genomic technologies Signup and view all the answers

What factors can determine the route of drug administration?

Drug properties and therapeutic objectives Signup and view all the answers

Which subfield of pharmacology deals with the effects of medication on behavior?

Neuro- and psychopharmacology Signup and view all the answers

What does ADME stand for in pharmacokinetics?

Absorption, Distribution, Metabolism, Excretion Signup and view all the answers

What occurs during first-order kinetics in drug metabolism?

A constant fraction of drug is metabolized per time unit. Signup and view all the answers

What happens to lipophilic drugs in the kidneys?

They are metabolized into polar substances in the liver. Signup and view all the answers

What is the primary function of phase I reactions in drug metabolism?

To convert lipophilic drugs into more polar molecules. Signup and view all the answers

Which equation represents the condition for zero-order kinetics?

Rate does not depend on drug concentration. Signup and view all the answers

What is the role of the cytochrome P-450 system in drug metabolism?

It catalyzes phase I metabolic processes. Signup and view all the answers

Which of the following is NOT true regarding zero-order kinetics?

It involves a constant fraction of drug metabolism per time unit. Signup and view all the answers

What may happen to pharmacologic activity during phase I metabolism?

It can decrease, increase, or remain unchanged. Signup and view all the answers

What is Vmax in the context of Michaelis-Menten kinetics?

The rate at which enzymes are saturated with a substrate. Signup and view all the answers

Which of the following is a Phase I reaction that does not involve the P-450 system?

Hydrolysis of procainamide Signup and view all the answers

What is the most common conjugation reaction in Phase II drug metabolism?

Glucuronidation Signup and view all the answers

Which of the following drugs undergoes Phase II metabolism before Phase I?

Isoniazid Signup and view all the answers

What is the normal glomerular filtration rate (GFR) in ml/min?

125 ml/min Signup and view all the answers

Which process allows free drug to flow into Bowman's space during glomerular filtration?

Glomerular capillary filtration Signup and view all the answers

Which drug's metabolite is often therapeutically inactive after Phase II reactions?

Acetaminophen Signup and view all the answers

What is the primary route for drug elimination from the body?

Through the kidneys into urine Signup and view all the answers

What happens to many drug metabolites that are too lipophilic to be retained in the kidney tubules?

They undergo further metabolism Signup and view all the answers

Study Notes

General Pharmacology

Pharmacology is the study of interactions between a living organism and exogenous chemicals that alter normal biochemical functions.
Pharmaceuticals are substances with medicinal properties.
A drug is a chemical substance used to treat, diagnose, or prevent (prophylaxis) a disease.
Pharmacology is a chemical science practiced by pharmacologists.
Sub-divisions include clinical pharmacology, neuro- and psychopharmacology, pharmacogenetics, pharmacogenomics, and pharmacoepidemiology. (These study drug effects on humans; behavior and nervous system function; genetic testing for drug use; application of genome technologies to drug discovery; and effects of drugs in large populations, respectively)
Toxicology is the study of harmful effects of drugs and the practice of diagnosing and treating exposures to toxins and toxicants.
Other subdivisions include pharmacodynamics and pharmacokinetics.

Introduction

Pharmacodynamics is the study of what a drug does to the body and its mechanism of action.
Pharmacokinetics is the study of what the body does to a drug — including absorption, distribution, metabolism, and excretion (ADME). (This describes how the drug moves throughout the body at the molecular level).

Routes of Drug Administration

Drug administration routes depend on the desired therapeutic outcome and the drug's properties (e.g., water or lipid solubility, ionization).
Enteral Routes
- Oral: Most common route, with drugs absorbed from the gastrointestinal tract. Encounter the liver, undergo first-pass metabolism before general circulation (limits efficacy, e.g., >90% of nitroglycerin cleared by the liver). Food can affect absorption for certain drugs (e.g., insulin, penicillin).
- Sublingual: Placement under the tongue for direct diffusion into the bloodstream and to avoid liver and potentially first-pass metabolism.
- Rectal: 50% of rectal region drainage bypasses portal circulation, minimizing liver transformation. Aids in drug absorption for drugs affected by intestinal enzymes or low PH of stomach.
Parenteral Routes
- Intravascular (IV): High drug concentration in blood, rapid onset, and avoids first-pass metabolism (but risks contamination, pain).
- Intramuscular (IM): Rapid absorption of drugs in aqueous solution. Slow absorption from depot preparations.
- Subcutaneous (SC): Minimizes risks of intravascular injection, but some combined with epinephrine for local vasoconstriction to reduce drug removal.
- Intradermal (ID): Injection into the dermis, usually for small volumes, like BCG vaccinations.
- Intraarticular: Injection into the joints, e.g. for pain relief.
- Intracardiac: Injection directly into the cardiac muscle, e.g. for cardiac arrest.
Other Routes
- Inhalation: For gases like anesthetics, and bronchodilators, absorption is rapid.
- Intranasal: For drugs like desmopressin (used to treat diabetes insipidus).
- Intrathecal/Intraventricular: For drugs needing direct entry into cerebrospinal fluid (CSF), especially in cases like acute lymphocytic leukemia.
- Topical: Drugs applied to the skin, like creams to treat skin infections, or eyedrops.
- Transdermal: For achieving systemic effects, usually using a patch, delivering drugs to the skin.

Absorption of Drugs

Absorption is the transfer of a drug from its administration site to the bloodstream.
It depends on drug transport from the GI tract, involving active and passive diffusion.
- Passive diffusion: Drug movement from a high concentration to a low concentration region without energy; driven by the concentration gradient.
- Active transport: Drug movement against the concentration gradient supported by energy from adenosine triphosphate (ATP) and specialized carrier proteins.
Effect of pH: Acidic drugs absorb better in acidic conditions; basic drugs absorb better in basic conditions (pH and ionization constant pKa determine the relative concentrations of a drug's charged and uncharged forms).
Other Factors: Blood flow influencing absorption; total absorbing areas (e.g., intestines), and how long drug remains in contact with the site

Bioavailability

Bioavailability: The fraction of administered drug gaining access to the systemic circulation in a chemically unchanged form.
Factors influencing bioavailability:
- First pass hepatic metabolism
- Drug solubility and stability
- Drug formulation: affects rate of absorption
Bioequivalence: Two related drugs are bioequivalent if they show comparable bioavailability and similar times to achieve peak blood concentrations.

Drug Distribution

Distribution: The process by which a drug moves from the bloodstream to the interstitial fluid of tissues and eventually into specific cellular compartments.
Blood flow plays a key role
Capillary permeability: Hydrophobic drugs cross capillaries more easily; ionized forms are absorbed less readily or not at all.
Binding of drugs to plasma proteins (e.g., albumin): This binding creates a reservoir of drug; only unbound drug can act on its target site.
Blood-brain barrier: Lipid-soluble drugs cross the blood-brain barrier more readily than water-soluble drugs.

Volume of Distribution (Vd)

Volume of Distribution (Vd): A hypothetical volume of fluid into which the drug is disseminated.
Factors affecting Vd include blood flow, capillary permeability, and drug binding to proteins.
The compartments of body water are used to compare Vd.
Vd = Dose given/plasma concentration

Drug Metabolism (Biotransformation)

Metabolism refers to reactions that convert a drug into a metabolite with changed properties, enabling possible excretion or further metabolism. This typically occurs in the liver, but other tissues can be involved.
Kinetics of metabolism:
- First order kinetics: Drug metabolism rate is proportional to drug concentration.
- Zero order kinetics: Drug metabolism rate is constant, regardless of drug concentration. This occurs at high doses when the enzymes involved are saturated or the metabolizing agents are rate-limiting.
Reactions of metabolism:
- Phase I reactions: Oxidation, reduction, hydrolysis, resulting in more polar molecules which can then undergo more excretion.
- Phase II reactions: Conjugation reactions making drugs more water-soluble and enabling excretion.
- Factors influencing drug metabolism, such as CYP450, in different phases

Drug Elimination

Elimination: Removal of drugs and their metabolites from the body.
Elimination methods:
- Renal elimination: Glomerular filtration; tubular secretion; active secretion
- Hepatic elimination: Metabolism by the liver, excretion into the bile
  -Other routes: Include lung, milk, and enterohepatic circulation for some drugs.
Body clearance: Total body clearance (CLTotal) is the sum of the clearances from all the eliminating organs (e.g., kidney, liver).
First order elimination kinetics: Drug concentration decreases exponentially during the course of elimination
Clinical situations resulting in increased drug half-life, thus requiring dosage adjustments: factors include reduced kidney function, drug-drug interactions.

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Description

Test your knowledge on key concepts related to pharmacology, drug absorption, and metabolism. This quiz covers the mechanisms of drug delivery, ionization, and the role of plasma proteins. Challenge yourself on questions that encompass drug properties and metabolic processes.