Pharmacology Chapter on Drug Absorption

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Questions and Answers

Which transport method does not require energy for drug absorption?

Facilitated Diffusion

Pinocytosis

Passive Transport (correct)

Active Transport

What role do carrier proteins play in facilitated diffusion during drug absorption?

They increase energy expenditure.

They aid in pinocytosis of drug particles.

They move drugs against a concentration gradient.

They transport drugs from high to low concentration. (correct)

Which type of transport mechanism involves engulfing drug particles into vesicles?

Facilitated Diffusion

Pinocytosis (correct)

Passive Transport

Active Transport

What process requires energy to transport drugs against a concentration gradient?

Active Transport Signup and view all the answers

What is the primary process by which drugs enter the bloodstream?

Absorption Signup and view all the answers

In which method does diffusion occur during drug absorption?

From high to low concentration Signup and view all the answers

Which organ metabolizes many drugs after they are absorbed from the GI tract?

Liver Signup and view all the answers

What effect does a reduction in the number of villi in the small intestine have on drug absorption?

Decreases absorption Signup and view all the answers

What is required for Active Transport to occur during drug absorption?

Energy input Signup and view all the answers

Which of the following correctly describes facilitated diffusion?

It requires membrane channels for drug transport. Signup and view all the answers

What term describes the metabolism of drugs to an inactive form in the liver after intestinal absorption?

First-pass effect Signup and view all the answers

Which route of administration involves drug absorption from the mucosal lining of the small intestine?

Oral Signup and view all the answers

Why is pinocytosis considered an active process?

It consumes energy to engulf substances. Signup and view all the answers

What is NOT one of the four processes involved in pharmacokinetics?

Drug synthesis Signup and view all the answers

How does the first-pass metabolism affect drug efficacy?

Decreases the amount of active drug Signup and view all the answers

Which of the following statements about enteral drug absorption is true?

It involves absorption across the mucosal lining of the small intestine. Signup and view all the answers

What is the primary route of drug excretion from the body?

Through the kidneys Signup and view all the answers

How does acidic urine affect the elimination of weak base drugs?

Promotes elimination Signup and view all the answers

Which factor is NOT included in the categories that affect drug excretion?

Urine osmolarity Signup and view all the answers

What is the primary effect of a drug defined as?

The desirable response Signup and view all the answers

Which of the following is NOT a common test to determine renal function?

Liver function tests Signup and view all the answers

Which property of a drug reflects the amount needed to elicit a specific physiological response?

Potency Signup and view all the answers

A drug with high potency, like fentanyl, is characterized by which of the following?

Significant therapeutic response at low concentrations Signup and view all the answers

What factor does alkaline urine promote regarding drug excretion?

Elimination of weak acids Signup and view all the answers

Which characteristic of a drug allows it to cross the blood-brain barrier (BBB) effectively?

High lipid solubility Signup and view all the answers

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

Liver Signup and view all the answers

How does the liver metabolize lipid-soluble drugs?

Converts them to water-soluble metabolites Signup and view all the answers

How long does it typically take for a drug to reach a steady state?

Four half-lives of the drug Signup and view all the answers

What is a loading dose?

An initial high dose to quickly achieve therapeutic levels Signup and view all the answers

What does the term 'half-life' refer to in pharmacokinetics?

The time required for drug concentration to be reduced by half Signup and view all the answers

Which factor does NOT influence the half-life of a drug?

Mode of administration Signup and view all the answers

What is necessary to achieve optimal therapeutic benefit from a drug?

Reaching a steady state concentration Signup and view all the answers

What must happen to solid drugs taken by mouth before they can be absorbed?

They must be dissolved into a liquid solution. Signup and view all the answers

Which process involves the breakdown of oral drugs into smaller particles?

Disintegration Signup and view all the answers

What role do excipients play in drug formulation?

They enable the drug to disintegrate and dissolve properly. Signup and view all the answers

What happens if a drug does not properly disintegrate in the gastrointestinal tract?

No absorption will occur, and the drug will be ineffective. Signup and view all the answers

Which of the following is true about drugs that come in liquid form?

They are already in solution and do not require dissolution. Signup and view all the answers

Which of the following is NOT a component typically found in tablets?

Liquid solvents Signup and view all the answers

What is the ultimate goal of the dissolution and disintegration processes in drug absorption?

To allow the drug to enter the bloodstream effectively. Signup and view all the answers

How does the presence of fillers affect drug tablets?

They assist in the size and shape of the tablets. Signup and view all the answers

What is the peak time for a drug administered intravenously?

30 to 60 minutes after infusion Signup and view all the answers

How are trough drug levels measured?

Just prior to the next dose of the drug Signup and view all the answers

Which receptor family is characterized by their presence in the cell nucleus?

Transcription factors Signup and view all the answers

What is primarily affected by the activation of ligand-gated ion channels?

Sodium and calcium ions Signup and view all the answers

What is the role of guanosine triphosphate (GTP) in receptor response?

It is involved in the binding of the G protein Signup and view all the answers

What type of receptors are involved in rapid activation upon ligand binding?

Ligand-gated ion channels Signup and view all the answers

Which component is NOT part of the three components involved in transcription factor activation?

The ligand Signup and view all the answers

What is the primary function of the trough drug level?

Indicates drug elimination rate Signup and view all the answers

Study Notes

Pharmacokinetics

Pharmacokinetics is the study of how drugs move throughout the body.
It's necessary to achieve drug action.
Four processes involved are absorption, distribution, metabolism (biotransformation), and excretion (elimination).

Drug Absorption

The movement of the drug into the bloodstream after administration.
Different routes affect absorption rates:
- Enteral (by mouth): Drugs absorbed across the lining of the small intestine.
- Intramuscular: Drugs absorbed faster in muscles with higher blood flow.
- Subcutaneous: Slower absorption due to decreased blood flow compared to muscle.
- Rectal: Slower absorption due to smaller surface area and lack of villi.

Drug Absorption - For Drugs Taken By Mouth (Enteral)

Most oral drugs are absorbed across the mucosal lining of the small intestine.
The lining is covered with villi to increase surface area for absorption.
Reduced villi can decrease absorption due to disease, drug effects, or removal of the small intestine.
After absorption, drugs enter the liver via the portal vein.
In the liver, some drugs are metabolized to an inactive form, which is excreted, reducing the active drug amount. This is first-pass metabolism.

Drug Absorption - Mechanisms of Absorption (Enteral)

Passive Transport: Drugs move across the membrane without energy, from high to low concentrations (Diffusion & Facilitated Diffusion).
Active Transport: Drugs move against their concentration gradient, requiring a carrier (enzyme or protein).
Pinocytosis: Cells engulf drug particles in a vesicle.

Drug Absorption - Dissolution

For the body to use drugs taken by mouth (solid form), they must dissolve into small particles in a liquid to form a solution.
This process is called dissolution.
Tablets aren't 100% drug; fillers (excipients) like syrup, gums, and honey improve dissolution.

Drug Absorption - Disintegration

Disintegration is the breakdown of a drug into smaller particles.
Drug disintegration and dissolution occur faster in acidic fluids (pH 1-2) compared to alkaline fluids (pH > 7).
Enteric-coated drugs resist disintegration in the stomach acid, dissolving only in the alkaline environment of the small intestine.

Bioavailability

The percentage of administered drug available for activity.
Affected by absorption and first-pass metabolism.
- Orally administered drugs usually have less than 100% bioavailability.
Factors affecting bioavailability:
- Drug form, administration route, gastric mucosa and motility, administration with food/other drugs, and liver function.

Factors Affecting Drug Absorption

Blood flow
Pain
Fasting
Food
pH
Stress
Hunger
Exercise

Intramuscular Absorption

Drugs injected into muscles are absorbed faster where blood flow is higher.

Subcutaneous Absorption

Absorption is slower in subcutaneous tissue than in muscle due to lower blood flow.

Rectal Absorption

Slower absorption than oral route due to smaller surface area and a lack of villi in the rectum.

Drug Distribution

Drug movement from circulation to body tissues.
Influenced by:
- Rate of flow to tissue
- Drug affinity to tissue
- Protein binding

Protein Binding

As drugs are distributed in the plasma, many bind to plasma proteins (albumin, lipoproteins, alpha-1-acid-glycoprotein [AGP]).
Acidic drugs (aspirin, methotrexate) & neutral drugs (nortriptyline) bind with albumin or lipoproteins. Basic drugs (morphine, amantadine) bind to AGP.
Highly protein-bound drugs are >90% bound to protein (Warfarin, Glyburide, Sertraline, Furosemide, Diazepam).
Bound portion is inactive; unbound portion is free and active.
Low plasma protein levels can increase free drug, leading to accumulation and toxicity.

Blood-Brain Barrier (BBB)

The BBB protects the brain from foreign substances (about 98% of drugs); tight junctions in the brain capillaries prevent most substances from crossing.
Lipid-soluble drugs (e.g., benzodiazepines) may cross through diffusion.
Water-soluble drugs struggle to cross.

Drug Metabolism (Biotransformation)

The body chemically changes drugs into a form that can be excreted.
Liver is the primary site of metabolism.
Liver enzymes (cytochrome P450 system) convert lipid-soluble drugs into water-soluble metabolites.
Water-soluble metabolites are then excreted.

Drug Half-Life

The time it takes for the amount of a drug in the body to reduce by half.
Factors affecting half-life include the amount of drug administered, previous doses, metabolism, and elimination.
Half-life is used to determine the dosing interval.

Steady State

A stable drug concentration in the body.
Achieved when the rate of drug administration equals the rate of drug elimination.

Drug Excretion

Elimination of drugs from the body. - Kidneys are the primary route of excretion. - Other routes include bile, lungs, saliva, sweat, and breast milk. - Kidneys filter free drugs, water-soluble drugs; drugs bound to protein aren't filtered.

Factors Affecting Drug Excretion

Urine pH: Acidic urine promotes excretion of weak base drugs; alkaline urine promotes excretion of weak acid drugs.
Prerenal conditions: reduced blood flow to kidneys decreases glomerular filtration.
Intrarenal conditions: affect glomerular filtration and tubular secretion/reabsorption.
Post renal conditions: adversely affect glomerular filtration.

Common Tests to Determine Renal Function

Creatinine: Metabolic by-product of muscle, excreted by the kidneys.
Blood Urea Nitrogen (BUN): Breakdown product of protein metabolism.

Pharmacodynamics

The study of how drugs affect the body.
A drug's primary effect is its desired response.
Secondary effects may be desirable or undesirable.

Dose-Response Relationship

The body's physiological response to changes in drug concentration at the site of action.
Potency- Amount of drug needed to achieve a specific response. (low potency-needs more drug for the desired response)
Maximal efficacy- Point where increasing the dose no longer increases the desired effect.
Therapeutic Index (TI)- The difference between the therapeutic dose (ED50) and the toxic dose (TD50); high TI is safer.
ED50 (effective dose in 50% of the population)
TD50 (toxic dose in 50% of the population)

Onset, Peak, and Duration of Action

Onset: Time it takes for a drug to reach the minimum effective concentration (MEC).
Peak: Highest drug concentration in the blood.
Duration: Length of time a drug exerts its therapeutic effect.

Therapeutic Drug Monitoring (TDM)

Plasma drug level: Highest concentration of the drug at a specific time, used to measure and monitor absorption rates.
- Peak time (oral 2-3 hrs; IV 30-60 mins; IM 2-4 hrs)
Trough drug level: Lowest drug concentration, measures drug elimination. Drawn right before the next dose.

Receptor Theory

Most receptors are proteins on cell surface membranes or within the cell.
Four receptor families:
- Cell membrane-embedded enzymes
- Ligand-gated ion channels
- G protein-coupled receptor systems
- Transcription factors

Agonists and Antagonists

Agonists: Drugs that activate receptors and produce a desired response.
Antagonists: Drugs that prevent receptor activation, blocking a response.

Nonspecific and Nonselective Drug Effects

Nonspecific: Drugs affecting multiple receptor sites, potentially producing undesirable effects besides the target site.
Nonselective: Drugs affecting multiple receptors, leading to multiple bodily effects (desirable/undesirable).

Mechanisms of Drug Action

Stimulation: Drugs enhancing intrinsic activity (e.g., increasing heart rate).
Depression: Drugs decreasing neural/bodily function (e.g., decreasing heart rate).
Irritation: Drugs causing a noxious effect.
Replacement: Drugs replacing essential body compounds (e.g., insulin).
Cytotoxic action: Drugs selectively killing invading organisms/cancers.
Antimicrobial medication: Drugs preventing, inhibiting, or killing infectious organisms.
Modification of immune system: Drugs modifying/enhancing/depressing the immune system.

Side Effects, Adverse Drug Reactions, and Drug Toxicity

Secondary effects of drug therapy (desirable/undesirable).
Adverse drug reactions can be unexpected, unintentional, while taking normal dosage, due to chronic illness, age, weight, gender, and ethnicity..
Drug toxicity occurs when drug levels exceed the therapeutic range, potentially from overdose, accumulation, disease, genetics, or age.

Pharmacogenetics

Study of how genetics affect an individual's response to a specific drug.
Genetic factors can change drug metabolism.
Can impact the absorption, distribution, metabolism, and excretion of the drug.
Pharmacogenomics aims to develop precision medicine based on a person's genetic makeup to enhance outcomes and safety.

Drug Interactions

An altered or modified drug action or effect due to one or more drugs.
- Pharmacokinetic interactions: Changes in absorption, distribution, metabolism, or excretion of one or more drugs.
- Pharmacodynamic interactions: Additive, synergistic, or antagonistic drug effects (combining two drugs with additive effects means that the combined effect of the two drugs is potentially greater than the sum of the individual effects. Synergistic effect- two drugs combining to produce a response greater than the effects of each drug. Antagonistic effect -two drugs that combine, and one drug reduces or blocks the effect of the other drug).
Common symptoms of drug-drug interactions: nausea, heartburn, headache, and lightheadedness.
Drug-nutrient interactions: Food can affect the body's response to drugs.
Drug-laboratory interactions: Drugs can affect clinical lab tests.

Drug-Induced Photosensitivity

Skin reaction caused by a drug and exposure to UV light.
Photoallergic reaction: Drug activates in the skin with UV light into a more allergenic compound & requires previous exposure.
Phototoxic reaction: Drug undergoes photochemical reaction with UV light to cause damage & doesn't involve the immune system, dose-related.

Examples of Drugs that Cause Photosensitivity

(List of Drugs)

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Test your knowledge on the various methods of drug absorption and transport mechanisms with this quiz. Explore processes such as facilitated diffusion, active transport, and the effects of intestinal health on drug metabolism. Ideal for students studying pharmacology and related fields.