General Pharmacology Quiz

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@FlawlessSparkle

Study Notes

Pharmacokinetics describes what the body does to a drug, including absorption, distribution, metabolism, and excretion.

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.

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).

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)

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.

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 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.

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

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 (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).