Pharmacology: Drug Transport and Absorption

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Questions and Answers

What is a disadvantage of the oral route of drug administration?

Drugs bypass the liver.

Drugs are always absorbed effectively.

Drugs have no interaction with food.

Drugs can lose potency due to metabolic processes. (correct)

Why is the sublingual route beneficial for certain drugs?

It is the most painless route available.

It bypasses the first-pass hepatic effect. (correct)

It provides direct access to the liver for drug metabolism.

It allows drugs to be absorbed through the stomach.

Which factor can cause irregular absorption of drugs administered orally?

Increased blood flow to the GI tract.

Frequent meals.

Decreased pH levels in the stomach. (correct)

Ingestion of non-lipid soluble drugs.

What is a primary reason for using the rectal route in certain patients?

Oral drugs have too high a first-pass effect. Signup and view all the answers

What can happen to a drug administered via the rectal route?

It can irritate the mucous membrane, leading to ejection. Signup and view all the answers

What type of diffusion is characterized by a direct proportionality to the concentration gradient on both sides of the membrane?

Passive diffusion Signup and view all the answers

What is true about the parenteral routes of drug administration?

They completely avoid the gastrointestinal tract. Signup and view all the answers

Which of the following drugs are most likely to be absorbed via passive diffusion?

Lipophilic, non-ionic, small molecules Signup and view all the answers

Which of the following is a common factor affecting oral drug absorption?

Drug-binding to food substances. Signup and view all the answers

Which factor is NOT likely to influence drug transport across membranes?

Height of the administration site Signup and view all the answers

What characteristic of drugs makes sublingual administration especially suitable for emergencies?

Drugs that are potent and lipid-soluble. Signup and view all the answers

What is the definition of drug absorption?

The passage of a drug from the site of administration across a biological barrier into plasma Signup and view all the answers

What characterizes aqueous transport of drugs?

Occurs through aqueous channels or pores Signup and view all the answers

Which statement is true regarding the influence of diet on drug transport?

Diet can affect the concentration gradient necessary for passive diffusion. Signup and view all the answers

Which type of transport requires energy to move drugs across cell membranes?

Carrier-mediated active transport Signup and view all the answers

How can disease impact drug transport processes?

By changing the permeability of biological membranes Signup and view all the answers

What is a primary advantage of the intravenous route of administration?

Controlled delivery of substances Signup and view all the answers

What is one disadvantage of using the intravenous route?

Technical difficulties in administration Signup and view all the answers

Which muscle generally has a faster rate of absorption when using the intramuscular route?

Deltoid Signup and view all the answers

What effect does obesity have on the absorption rate of intramuscular injections?

Decreases absorption due to adipose tissue Signup and view all the answers

Which statement correctly describes the characteristics of the intramuscular route?

Absorption can be influenced by drug formulation Signup and view all the answers

Which non-injection route is NOT mentioned in the given information?

Oral Signup and view all the answers

What could be a consequence of too rapid delivery of large volumes via intravenous administration?

Development of embolisms Signup and view all the answers

Which factor does NOT influence the rate of absorption for intramuscular injections?

Time of day administered Signup and view all the answers

Which characteristic allows highly lipophilic drugs to pass the blood-brain barrier?

Lipid solubility Signup and view all the answers

What is a potential risk of lipid-soluble drugs during pregnancy?

They may cause developmental toxicity to the fetus Signup and view all the answers

How does organ perfusion influence drug distribution?

It decreases the drug concentration in less perfused organs Signup and view all the answers

Which of the following is true regarding basic drugs in breast milk?

They concentrate due to the acidity of breast milk Signup and view all the answers

What is one challenge in treating brain conditions with medication?

The presence of the blood-brain barrier Signup and view all the answers

What volume of distribution (Vd) indicates that a drug is likely stored in a depot?

Vd > 46L Signup and view all the answers

Which characteristic is associated with a small volume of distribution?

Low tissue binding levels Signup and view all the answers

Which drug is likely to be confined to the plasma compartment and cannot cross the capillary wall?

Heparin Signup and view all the answers

If a drug has a volume of distribution of 2L, what does this suggest about its distribution?

Distributed in plasma only Signup and view all the answers

What condition applies to obese patients when calculating drug distribution volumes?

Use ideal body weight Signup and view all the answers

Which of the following drugs would be distributed throughout body water?

Morphine Signup and view all the answers

Which statement correctly describes high volume of distribution for a drug?

High tissue binding levels Signup and view all the answers

Which drug class is likely distributed in the extracellular fluid compartment?

Penicillins Signup and view all the answers

Study Notes

Drug Transport Across Membranes

Passive diffusion is the movement of molecules across a membrane from a region of high concentration to a region of low concentration.
- Passive diffusion does not require energy or a carrier protein.
- The process is rapid for lipophilic, non-ionic, small molecules.
Aqueous transport is the passage of molecules through channels or pores in the cell membrane.
- This process is only possible for small, hydrophilic drugs.

Drug Absorption

Drug absorption is the process by which a drug enters the bloodstream from the site of administration.
- The drug must cross a biological membrane/barrier to enter the bloodstream
- The rate of absorption depends on factors such as the drug's properties, the route of administration, and the individual's physiological state.

Routes of Administration

Oral route:
- Drugs are taken by mouth.
- Most common and convenient route of administration.
- Advantages:
  - The most convenient route.
  - Safer than parenteral routes.
  - Economical and readily available.
- Disadvantages:
  - Can be affected by food and other drugs.
  - May not be suitable for all drugs.
  - First-pass effect can greatly reduce the bioavailability of the drug.
Sublingual route:
- Drugs are placed under the tongue.
- The drug is absorbed rapidly and bypasses the first-pass effect.
- Advantages:
  - Rapid onset of action.
  - Bypasses first-pass metabolism.
- Disadvantages:
  - Not suitable for all drugs.
  - Can be difficult to administer.
Rectal route:
- Drugs are administered rectally.
- Advantages:
  - Useful when oral administration is not feasible.
- Disadvantages:
  - Absorption may be irregular or incomplete.
  - Can be irritating to the rectal mucosa.
Parenteral routes:
- Includes any route that bypasses the gastrointestinal tract.
- These routes include:
  - Intravenous (IV):
    - Direct injection into a vein.
    - Advantages:
      - Rapid onset of action.
      - 100% bioavailability.
      - Controlled dosage.
      - Suitable for irritating drugs.
    - Disadvantages:
      - Greater risk associated with toxicity.
    - Requires medical skill and a sterile environment.
  - Intramuscular (IM):
    - Injection into a muscle.
    - Advantages:
      - Faster absorption than subcutaneous.
      - More convenient than IV.
      - Larger volumes can be administered.
    - Disadvantages:
      - Can be painful.
  - Subcutaneous:
    - Injection into the subcutaneous tissue.
    - Advantages:
      - Less irritating than IM.
      - Easier administration than IV or IM.
    - Disadvantages:
      - Slower absorption than IM or IV.
  - Transdermal:
    - Administration through the skin.
    - Advantages:
      - Convenient and painless.
      - Provides sustained release for longer duration.
    - Disadvantages:
      - Not suitable for all drugs.
  - Transmucosal:
    - Administration across the mucous membranes.
    - Advantages:
      - Rapid absorption.
      - Bypasses first-pass metabolism.
    - Disadvantages:
      - Not suitable for all drugs.

Drug Distribution

Distribution is the process by which a drug is transported from the bloodstream to the tissues.
- The rate of distribution depends on factors such as the drug's properties, the blood flow to the tissues, and the permeability of the membranes.
Factors that influence drug distribution:
- Plasma protein binding:
  - Many drugs bind to plasma proteins and are prevented from reaching their target sites.
- Blood-brain barrier:
  - A highly selective barrier that protects the brain from harmful substances.
  - Only lipophilic drugs easily cross this barrier.
- Blood-placenta barrier:
  - A protective barrier that prevents most drugs from reaching the fetus.
  - Only lipophilic drugs pass through this barrier, which can be harmful to the developing fetus.
- Mammary transfer:
  - Breast milk is acidic, which leads to a higher concentration of basic drugs in this fluid.
  - Non-electrolyte drugs (do not depend on pH gradient – e.g.alcohol) readily reaches the same concn as in the plasma.
- Organ/tissue perfusion:
  - The amount of drug reaching each tissue or organ depends on blood flow
  - Organs with higher blood flow receive more drug.
Volume of distribution (Vd):
- The apparent volume of distribution of a drug is the volume of fluid that would be required to contain the total amount of drug in the body at the same concentration as in the plasma.
- It is a measure of the extent to which a drug distributes throughout the body.
- A high Vd indicates that the drug is extensively distributed into the tissues.
- Obese patients need to have their volumes calculated using their ideal body weight.
Lipid soluble drugs:
- Can reach all the compartments of the body and may accumulate in body fat.
Small Vd:
- Low lipid solubility properties of the drug.
- High degree of plasma protein binding.
- Low level of tissue binding.
High Vd:
- Lipid solubility properties of the drug is high.
- Low degree of plasma protein binding.
- High degree of tissue binding.
Drugs confined to plasma compartment:
- Heparin, insulin (large molecules that cannot cross the capillary wall).
Drugs distributed in the ECF compartment:
- Aminoglycosides, Penicillins, suxamethonium, Tubocurarine.
Drugs distributed throughout body water:
- Phenobarbitone, Phenytoin, Alcohol, Amitryptilline, Haloperidol, morphine.

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Description

This quiz covers key concepts related to drug transport across membranes, including passive diffusion and aqueous transport. Additionally, it explores drug absorption and different routes of administration, focusing on how drugs enter the bloodstream. Test your understanding of these critical pharmacological principles.