General Pharmacology Quiz

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

• Patient-related factors:
  • Route of administration (IV, inhalation, IM, SC, oral, topical).
  • Absorbing surface (vascularity, surface area).
  • Pathological conditions (diarrhea).
• 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.

• 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).
• 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
• 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).