Podcast
Questions and Answers
What is the primary purpose of drug metabolism in the liver?
What is the primary purpose of drug metabolism in the liver?
Which enzyme system is primarily responsible for phase one metabolism in the liver?
Which enzyme system is primarily responsible for phase one metabolism in the liver?
How does the composition of body fat change across the lifespan in terms of pharmacokinetics?
How does the composition of body fat change across the lifespan in terms of pharmacokinetics?
What factor affects excretion most commonly across the lifespan?
What factor affects excretion most commonly across the lifespan?
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Which statement is true regarding infants and drug metabolism?
Which statement is true regarding infants and drug metabolism?
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What is a key physiological factor affecting drug distribution across the blood brain barrier?
What is a key physiological factor affecting drug distribution across the blood brain barrier?
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What is the most common route of excretion for drug byproducts in the body?
What is the most common route of excretion for drug byproducts in the body?
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What typically decreases in older adults that affects drug metabolism?
What typically decreases in older adults that affects drug metabolism?
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What is the main focus of pharmacodynamics?
What is the main focus of pharmacodynamics?
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Which route of drug administration is least affected by the first-pass effect?
Which route of drug administration is least affected by the first-pass effect?
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Which factor primarily affects gastric absorption in neonates and pediatric patients?
Which factor primarily affects gastric absorption in neonates and pediatric patients?
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Lipid-soluble drugs tend to concentrate in which body compartment?
Lipid-soluble drugs tend to concentrate in which body compartment?
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Which of the following factors affects drug absorption in older adults?
Which of the following factors affects drug absorption in older adults?
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The distribution of drugs in the body is largely influenced by what factor?
The distribution of drugs in the body is largely influenced by what factor?
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What effect does first-pass metabolism have on oral drugs?
What effect does first-pass metabolism have on oral drugs?
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What is the role of the liver in pharmacokinetics?
What is the role of the liver in pharmacokinetics?
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Study Notes
Introduction to Pharmacology
- Aims of the session:
- Outline principles of how drugs work
- Explain the effects of absorption, distribution, metabolism, and excretion on a drug's action
Definitions
- Pharmacology:
- The science that explores the composition, effects, and uses of drugs.
- Pharmacokinetics:
- What the body does to the drug
- Pharmacodynamics:
- What the drug does to the body
Pharmacokinetics
- Absorption:
- Drug at the site of administration
- Distribution:
- Drug in the circulation
- Distribution in tissues & body fluids
- Metabolism:
- Drug metabolism
- Excretion:
- Drug excretion
Absorption and Factors Affecting Absorption
- Oral
- Topical or transdermal
- Subcutaneous
- Intramuscular
- Intravenous
- Inhalation
- Rectal
- Factors:
- First-pass effect
- Destruction by enzymes
- Food
- Other medications
- Controlled release drugs
- Enteric coated drugs
Factors Affecting Absorption Across the Lifespan
- Neonate and Paediatric:
- Gastric absorption – acid-producing cells immature
- Gastric emptying - may be decreased
- Liver not fully mature - ↓ first-pass metabolism with ↑ drug levels in the bloodstream
- Older Adult:
- ↓ blood flow to tissues in GI tract
- Changes to gastric pH
- Variations in available plasma proteins
- ↓ subcutaneous fat
- Potential ↓ in cardiac output
Distribution
- Drugs do not distribute evenly throughout the body
- Lipid (fat) soluble drugs concentrate in adipose tissues
- Water soluble drugs concentrate in body water, blood, and interstitial fluid surrounding cells
- Some drugs concentrate in one part of the body
- Drugs penetrate body tissues at different speeds depending on their ability to cross cell membranes
- Blood-brain barrier (BBB) is a selective semipermeable membrane separating the brain
Factors Affecting Distribution Across the Lifespan
- Neonate and Paediatric:
- ↓ fat content
- ↓ protein binding capacity
- Blood-brain barrier still developing
- Older Adult:
- ↑ body fat
- ↓ serum albumin
Metabolism
- Metabolism comes from the Greek word that means "to change"
- Liver is the primary site for drug metabolism
- Main purpose to change the drug to become more water-soluble
- Can reduce drug activity or create other active metabolites
- Two phases of metabolism
- Phase one: Primarily in the liver by cytochrome P450 (CYP4 enzymes)
- Phase two: A large ionized molecule is added to the drug, increasing its water solubility
Factors Affecting Metabolism Across the Lifespan
- Neonate and Paediatric:
- Infants and children – Liver not fully developed ↓ enzymes
- Older Children ↑ metabolism
- Older Adult:
- ↓ metabolism in liver
- ↓ first-pass metabolism
Excretion
- Final stage of drug interaction
- Routes:
- Kidney – most common route, filters blood, majority of byproducts excreted in urine
- Liver – filters blood, some drugs and their metabolites actively transported to bile
- Other – Sweat, tears, reproductive fluids (e.g., seminal fluid), and breast milk can contain drugs and metabolites
Factors Affecting Excretion Across the Lifespan
- Neonate and Paediatric:
- Immature kidneys
- Older Adult:
- ↓ kidney function
- ↓ liver function
Therapeutic Window
- A range of drug concentrations in the plasma that is effective and does not cause toxicity
- Minimum toxic concentration
- Minimum effective concentration
Factors Affecting Pharmacokinetics
- Patient Factors:
- Age, sex, medical conditions, pregnancy
- Drug Factors:
- Solubility in water/lipid; size, electric charge
- Physiological Factors:
- First-pass effect, barriers (e.g., blood-brain barrier)
Task
- Download or find a copy of the BNF
- Identify pharmacokinetic information for:
- Metformin
- Ibuprofen
- Penicillin (Phenoxymethylpenicillin)
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Description
This quiz covers the fundamental principles of pharmacology, including the basic concepts of pharmacokinetics and pharmacodynamics. Understand how drugs are absorbed, distributed, metabolized, and excreted by the body. Explore various routes of drug administration and factors affecting their absorption.
