Pharmacology and Pharmacokinetics Quiz

Study Notes

Pharmacology

The study of drugs and how the body responds to them.

Pharmacokinetics

How drugs move through the body.

Pharmacokinetic Processes

Absorption: How the drug enters the bloodstream.
- Primarily takes place in the duodenum of the small intestine.
- Oral drugs need to disintegrate (break down) and dissolve before absorption.
- Excipients, like simple syrup and honey, can enhance drug dissolution.
- Factors that affect absorption:
  - Drug form: Liquids are absorbed faster than solids.
  - Gastric acidity: Higher acidity (pH 1 or 2) leads to faster absorption. Infants and older adults have lower gastric acidity.
  - Food intake: Food can interfere with absorption; some medications need to be taken with meals.
  - Other factors: Blood flow, pain, stress, hunger, fasting, and pH can all play a role in absorption.
- Rectal absorption is slower than oral.
- Parenteral routes: These bypass the digestive tract:
  - IM (Intramuscular): Injected into the muscle.
  - IV (Intravenous): Directly into the vein.
  - SUBQ (Subcutaneous): Injected under the skin.
  - ID (Intradermal): Injected into the skin.
- First Pass Effect:
  - Oral drugs are absorbed into the portal vein and go to the liver.
  - The liver contains enzymes that can inactivate the drug, reducing its bioavailability.
  - Bioavailability: The percentage of the drug that reaches systemic circulation and is available for activity. Oral bioavailability is always less than 100%.
Distribution: How the drug moves throughout the body from the bloodstream to tissues.
- Highly-perfused organs (heart, kidneys, liver) receive more drug.
- Slightly perfused organs (muscles, fat, peripheral organs) receive less drug.
- Factors affecting distribution:
  - Vascular and cellular permeability: How easily the drug can pass through blood vessels and cell membranes.
  - Regional blood flow and pH: Blood flow and pH differences between tissues can affect distribution.
  - Cardiac output: The amount of blood pumped by the heart influences drug distribution.
  - Tissue perfusion: How much blood is reaching specific tissues.
  - Drug binding to proteins:
    - Drugs can bind to proteins like albumin and lipoproteins in the bloodstream, which makes them inactive and less available for distribution.
    - Highly protein-bound drugs: Have a larger portion of the drug bound to proteins.
    - Weakly protein-bound drugs: Have a smaller portion of the drug bound to proteins.
Metabolism: Chemical breakdown of the drug in the body.
- The liver is the primary site of metabolism.
- Biotransformation: The process of converting drugs into a form that can be excreted.
- Prodrugs: Inactive compounds that are activated by metabolism in the body.
  - Example: Inactive form → Liver → Active form
- P450 system: Enzymes in the liver that convert lipid-soluble drugs into water-soluble forms for excretion.
- Half-life: The time it takes for the amount of drug in the body to be reduced by half.
- Steady state: When the rate of drug administration equals the rate of drug elimination (rate in = rate out). It usually takes about 4 days to achieve steady state.
- Loading dose: A large initial dose given to quickly reach therapeutic levels, often used in emergency situations. Given only once.
Excretion: How the drug is eliminated from the body.
- The kidneys are the primary route of excretion.
- Other routes of excretion: Bile, lungs, saliva, sweat, breast milk.
- Urine pH: Influences drug excretion:
  - Alkaline urine: Excretes weak acid drugs more efficiently.
  - Acidic urine: Excretes weak base drugs more efficiently.
- Conditions affecting excretion:
  - Prerenal: Before the kidneys (e.g., dehydration, hemorrhage).
  - Intrarenal: Within the kidneys (e.g., chronic kidney disease).
  - Postrenal: After the kidneys (e.g., kidney stones).
- Blood Urea Nitrogen (BUN) and Creatinine: Tests used to assess kidney function and may influence drug dosage.