Pharmacology Drug Absorption Quiz

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Questions and Answers

Which mechanism of drug absorption requires energy due to the movement against the concentration gradient?

Passive diffusion

Endocytosis

Facilitated diffusion

Active transport (correct)

What is the primary determinant of the absorption rate for intravenous administration of drugs?

Chemical structure of the drug

Route of administration (correct)

Vascularity of the tissue

Intrinsic factor availability

Which factor would most likely enhance the absorption of a drug administered orally?

Low vascularity of the intestines

High molecular weight of the drug

Presence of certain food items

Large surface area of the intestine (correct)

Which method of absorption allows drugs with high molecular weight to enter the cell?

Endocytosis Signup and view all the answers

What's the primary role of pharmacokinetics in drug action?

Analyzing drug absorption, distribution, metabolism, and excretion Signup and view all the answers

What effect does shock have on drug absorption through oral and subcutaneous routes?

Decreases absorption Signup and view all the answers

Which factor influences drug absorption based on the condition of the body?

All of the above Signup and view all the answers

Which route of drug administration has the least absorption efficiency?

Topical Signup and view all the answers

What occurs when a free form of a drug is metabolized or excreted?

An equal amount is released from plasma protein binding sites. Signup and view all the answers

Which statement about the blood-brain barrier (BBB) is true?

It is more permeable during states of inflammation. Signup and view all the answers

What is the primary role of biotransformation in drug metabolism?

To transform unionized drugs into ionized, water-soluble metabolites. Signup and view all the answers

Which of the following can result from enzyme induction?

Enhanced drug interactions. Signup and view all the answers

What factor most significantly impacts the change in elimination half-life (t1/2) of a drug?

Physiological changes and drug interactions. Signup and view all the answers

Which of the following statements about the kidney's role in drug excretion is accurate?

Excretion occurs through various processes in different parts of the kidney. Signup and view all the answers

Which consequence can occur from enzyme inhibition in drug metabolism?

Duration of action of some drugs is prolonged. Signup and view all the answers

What is the main consequence of a drug passing the placental barrier during pregnancy?

Increased risk of teratogenicity. Signup and view all the answers

Which statement about the solubility of drugs in relation to pH is accurate?

Weak bases are more soluble in alkaline solutions. Signup and view all the answers

How does lipid solubility affect drug absorption?

Higher lipid solubility increases drug absorption. Signup and view all the answers

What is the impact of pharmaceutical preparation on drug absorption?

Solutions are absorbed better than suspensions and tablets. Signup and view all the answers

Which statement about iron absorption is true?

Ferrous iron (Fe+2) is absorbed better than ferric iron (Fe+3). Signup and view all the answers

How does the first-pass effect influence drug bioavailability?

It decreases the percentage of drug that reaches systemic circulation. Signup and view all the answers

In what way does pKa influence drug absorption?

A substance becomes more lipid-soluble in solutions with pH differing from its pKa. Signup and view all the answers

Which of the following factors does NOT affect drug distribution?

Drug ionization. Signup and view all the answers

What determines the bioavailability of a drug administered intravenously?

The route of administration is always 100%. Signup and view all the answers

Study Notes

General Pharmacology

Pharmacology is the science of drugs.
Drugs are substances used to prevent, diagnose, and treat diseases.

Pharmacokinetics

Pharmacokinetics describes what the body does to a drug.
This includes absorption, distribution, metabolism, and excretion (ADME).

Absorption

Absorption is the passage of a drug from the site of administration to systemic circulation.
Mechanisms of drug absorption include passive diffusion.
- Passive diffusion is the most common and important mechanism by which drugs cross biological membranes. This involves movement of water-soluble drugs across aqueous pores and lipid-soluble drugs across the cell membrane.
Other mechanisms of drug absorption include carrier-mediated transport.
- Facilitated diffusion: This process does not require energy, and the drug moves along a concentration gradient, assisted by a carrier protein.
- Active transport: Energy (ATP) is needed, and the drug moves against a concentration gradient, using a carrier protein.
Another mechanism for absorption is endocytosis and exocytosis, where a drug of high molecular weight binds to the cell membrane and gets enclosed for movement into or outside the cell.

Route of administration: IV and inhalation are faster than IM, SC, oral and topical.
Absorbing surface: Skeletal muscle has higher vascularity than subcutaneous tissue, while the intestine has more surface area than the stomach.
Pathological conditions: Conditions like diarrhea can decrease oral absorption.

Water and lipid solubility: More lipid-soluble drugs are absorbed easier.
Valency: Ferrous iron (Fe++) is absorbed better than ferric iron (Fe+++).
Nature: Inorganic compounds are generally absorbed better than organic compounds.
Pharmaceutical preparations: Different dosage forms like solutions are better absorbed than suspensions or tablets. Excipients like calcium (Ca++) can decrease absorption of some drugs.
Ionization of the drug: Unionized drugs are more lipid soluble and absorbed easily.

Factors Affecting Absorption (Additional)

Systemic circulation: Shock can decrease absorption.
Specific factors: Intrinsic factor is crucial for vitamin B12 absorption.
Coadministration factors: Other drugs and food can affect absorption, including adrenaline, which can reduce local anesthetic absorption and calcium reducing tetracycline absorption

The Effect of pH on Drug Ionization

Most drugs are weak acids or bases.
Weak acids are better absorbed in acidic environments (low pH), while weak bases are better absorbed in alkaline environments (high pH).
The pH at which the ionized and unionized forms of a drug are equal is the pKa.
A smaller pKa value indicates a stronger acid, while a larger pKa value indicates a weaker acid.

Bioavailability

Bioavailability is the percentage of a drug reaching systemic circulation and available for biological effect.
Factors affecting bioavailability include:
- Extent of drug absorption
- Route of administration (e.g., IV has 100% bioavailability)
- First-pass effect (metabolism of a drug before it reaches systemic circulation, e.g., in the liver or intestines)

Drug Distribution

After absorption, drugs are distributed to one or more body compartments.
Compartments include vascular, vascular and interstitial, and vascular, interstitial, and intracellular compartments.
Factors affecting drug distribution involve:
- Blood flow – delivery to an organ is proportional to blood flow
- Lipophilicity – affects the ability of drug to cross cell membranes
- Plasma protein binding – drugs exist in bound (inactive) and free (active) forms, impacting distribution
- Binding to tissues – drug accumulation in particular tissues like the thyroid

Blood-Brain Barrier (BBB) and Placental Barrier

BBB: Only lipid-soluble drugs can pass due to the structure of capillaries in the brain. Inflammation can increase permeability.
Placental barrier: Drugs that pass the barrier can affect the fetus during pregnancy (teratogenicity) or during labor (neonatal asphyxia).

Drug Metabolism (Biotransformation)

Key importance of metabolism is converting unionized drugs into ionized, water-soluble metabolites for easier excretion.
The liver is the primary organ, but metabolism can also occur in other organs like lungs, kidneys, and intestines.
Consequences of drug metabolism include:
- Converting active drugs to inactive metabolites.
- Converting inactive prodrugs to active drugs.
- Converting active drugs to active metabolites.
- Converting drugs to toxic metabolites (e.g., paracetamol to hepatotoxic epoxides).

Factors Affecting Biotransformation

Physiological changes (age, sex)
Pathological factors (e.g., liver cell failure)
Enzyme induction/inhibition

Drug Excretion

The kidney is the primary organ for drug excretion, with excretion happening via glomerular filtration, proximal convoluted tubules (PCT), and distal convoluted tubules.
Other sites of excretion include bile and lungs.

Elimination Half-Life

Elimination half-life (t1/2) is the time it takes for the plasma concentration of a drug to reduce to half of its initial concentration.
The importance of half-life relates to determining dosing intervals. Short half lives result in frequent dosing, whereas long half-lives allow for less frequent dosing.

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Description

Test your knowledge on the mechanisms of drug absorption and the factors affecting pharmacokinetics. This quiz covers various aspects of drug administration, absorption rates, and the influence of body conditions on drug effectiveness. Ideal for students studying pharmacology or related fields.