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Questions and Answers
Which mechanism of drug absorption requires energy and operates against the concentration gradient?
Which mechanism of drug absorption requires energy and operates against the concentration gradient?
Which factor related to the patient can significantly decrease oral drug absorption?
Which factor related to the patient can significantly decrease oral drug absorption?
What characterizes facilitated diffusion in drug absorption?
What characterizes facilitated diffusion in drug absorption?
Which route of administration is associated with the fastest absorption of drugs into systemic circulation?
Which route of administration is associated with the fastest absorption of drugs into systemic circulation?
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Which statement accurately describes the role of intrinsic factors in drug absorption?
Which statement accurately describes the role of intrinsic factors in drug absorption?
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Which factor would most negatively affect the absorption of tetracyclines?
Which factor would most negatively affect the absorption of tetracyclines?
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What happens to weak acids in an acidic solution regarding lipid solubility?
What happens to weak acids in an acidic solution regarding lipid solubility?
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Which statement accurately describes the effects of pH on drug absorption?
Which statement accurately describes the effects of pH on drug absorption?
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Which of the following factors is not directly related to the bioavailability of a drug?
Which of the following factors is not directly related to the bioavailability of a drug?
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How does lipophilicity affect the distribution of drugs in the body?
How does lipophilicity affect the distribution of drugs in the body?
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Study Notes
General Pharmacology
- Pharmacology is the science of drugs.
- Drugs are substances used to prevent, diagnose, and treat diseases.
Pharmacokinetics (ADME)
- Pharmacokinetics describes what the body does to a drug, including absorption, distribution, metabolism, and excretion.
Absorption
- Absorption is the passage of a drug from the site of administration to systemic circulation.
- Passive diffusion is the most common absorption mechanism.
- Water-soluble drugs pass through aqueous pores.
- Lipid-soluble drugs pass through the cell membrane.
- Carrier-mediated transport includes:
- Facilitated diffusion: no energy required, moves along the concentration gradient.
- Active transport: energy (ATP) required, moves against the concentration gradient.
- Endocytosis and exocytosis: high molecular weight drugs bind to the cell membrane and are enveloped to move inside or outside the cell.
Factors Affecting Absorption
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Patient-related factors:
- Route of administration (IV, inhalation, IM, SC, oral, topical).
- Absorbing surface (vascularity, surface area).
- Pathological conditions (diarrhea).
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Drug-related factors:
- Water and lipid solubility (higher lipid solubility, higher absorption).
- Valency (ferrous iron is better absorbed than ferric iron).
- Nature (inorganic compounds are better absorbed than organic compounds).
- Dosage form (solution > suspension > tablet).
- Excipients (e.g., calcium).
- Ionization (ionized drugs are less lipid-soluble and absorbed).
Factors Affecting Absorption, cont.
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Systemic circulation: Shock decreases absorption
- Oral and subcutaneous routes are unsuitable.
- Specific factors: Intrinsic factor is essential for Vitamin B12 absorption.
- Co-administration: Co-administration of other drugs or food can affect absorption. (e.g., SC adrenaline changes blood vessel states which changes absorption rate of local anesthetics)
Systemic Circulation
- The passage of drug through systemic circulation from absorption site.
Blood-brain Barrier and Placental Barrier
- Blood-brain barrier: Lipid-soluble drugs can pass due to the thick basement membrane surrounding the glial tissues
- Placental barrier: Drugs passing can cause teratogenicity during pregnancy and neonatal asphyxia during labour.
Drug Distribution
- After absorption, the drug is distributed to one or more body compartments (vascular, vascular & interstitial, vascular, interstitial, and intracellular).
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Factors affecting distribution:
- Blood flow (proportional to blood flow).
- Lipophilicity (depends on drug's lipid-solubility).
- Plasma protein binding (drugs bind in the blood to become either bound/unbound):
- Bound form: inactive, non-diffusible, cannot be metabolized or excreted.
- Free form: active, diffusible, can be metabolized or excreted.
- Drug binding to tissues (e.g., iodides in thyroid and salivary glands).
Metabolism (Biotransformation)
- Metabolism converts unionized drugs to ionized, water-soluble metabolites for easier excretion.
- The liver is the main organ of metabolism but can occur in the lungs, kidneys, and intestines.
Consequences of Drug Metabolism
- Active to inactive metabolite (most drugs).
- Inactive prodrug to active drug.
- Active drug to active metabolite.
- Conversion to toxic metabolites (e.g., paracetamol to hepatotoxic epoxides).
Factors Affecting Biotransformation
- Physiological factors (age and sex).
- Pathological factors (liver cell failure).
- Enzyme induction and inhibition
Consequences of Enzyme Induction and Inhibition
- Enzyme induction Consequences: - Failure of drug action - Drug interactions
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Enzyme inhibition Consequences:
- Exaggerated pharmacological actions and adverse effects
- Increased duration of action and half-life of some drugs
- Drug interactions
Excretion of Drugs
- Kidneys are the primary organs of drug excretion
- Excretion mechanisms:
- Glomerular filtration
- Proximal convoluted tubules (PCT)
- Distal convoluted tubules
- Other excretion sites: Bile and lungs
Elimination Half-Life
- Elimination half-life (t1/2) is the time it takes for plasma concentration of a drug to reduce to half of its initial concentration.
- Importance of elimination half-life
- Dosage interval (T)
- IV infusion (short half-life)
- Loading and maintenance doses (long half-life).
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Description
Test your knowledge on the fundamentals of pharmacology, including pharmacokinetics and the absorption of drugs. This quiz covers the mechanisms of drug absorption and factors that can influence it. Get ready to deepen your understanding of how drugs interact with the body.
