General Principles of Pharmacology

Question 1

What are three physicochemical properties of drugs?

Answer 1

Molecular size

Degree of fat and water solubility - determined by polarity

Charge - determined by acidic, basic or neutral nature

Question 2

What is the partition coefficient?

Answer 2

Measure of overall polarity

P.C. = [Drug in fat or lipid]/[Drug in water]

(PC > 1 ; lipophilic, PC< 1 ; hydrophilic)

Question 3

What are three ways drugs cross biological membranes?

Answer 3

Filtration through pores

Passive diffusion across lipid-like membranes (uncharged drugs)

Active transport (charged drugs)

Question 4

What is the rate of filtration dependent on?

Answer 4

Pressure gradient and size of the drug

Question 5

What is the rate of active drug transport dependent on?

Answer 5

Binding capacity of the drug species and the limited availability of the carrier

Question 6

What are three general routes of administration?

Answer 6

Enteral - placing drug into some portion of GI tract

Parenteral - placing drug into some portion of body other than the GI tract

Topical - placing the drug onto the surface of tissue

Question 7

Describe oral administration.

Answer 7

Absorption occurs primarily via passive diffusion

Rate depends on rate of dissolution, PC of druge and chemical nature of the drug

SI has a larger surface area than stomach

First pass elimination

Question 8

Describe sublingual administration.

Answer 8

Absorbed via passive diffusion

Drugs enter general circulation before passing through liver

Question 9

Describe rectal administration.

Answer 9

Absorbed via passive diffusion

Drugs enter general circulation before passing through the liver

Question 10

Describe Subcutaneous administration.

Answer 10

Absorption occurs by passive diffusion through capillary membranes - lipid soluble drugs

Rate of absorption depends on blood flow to injection site

Question 11

Describe intramuscular administration.

Answer 11

Good for orally labile drugs

Depot preparations (e.g. contraceptives)

Question 12

Describe intravenous administration

Answer 12

Rapid onset of action, known amount of drug delivered

Drug cannot be withdrawn or absorption retarded

Question 13

Describe intraarterial administration

Answer 13

Achieve high concentration of drug into one body site

Cancer

Question 14

Describe inhalation administration

Answer 14

Primarily used for anesthetic/analgesic gases

Absorption occurs via passive diffusion (must dissolve in pulmonary fluids prior to absorption)

Question 15

Describe intrathecal administration.

Answer 15

Injection into spinal subarachnoid space

Used in spinal anesthesia and CNS chemotherapy

Question 16

What factors affect drug distribution?

Answer 16

Physicochemical properties

Nature of membrane encountered

Protein binding and storage

Blood perfusing a given tissue

Disease states

Question 17

How do drugs cross the blood-brain barrier?

Answer 17

Passive diffusion

Question 18

How do drugs cross the blood-CSF barrier?

Answer 18

Passive diffustion at ventricles or via active bidirectional transport systems in the choroid plexuse

Active transport primarily out of CSF and into blood

Question 19

Why do drugs enter the fetus?

Answer 19

Placenta is similar to a large capillary bed; exchange of fluids and nutrients with the mother

Question 20

What is protein binding?

Answer 20

Affects storage and redistribution of drugs

Mostly albumin and a-glycoprotein

Bonds can be different strength, mostly reversible

Question 21

Describe protein binding interactions

Answer 21

Occurs when a substance competes with a drug for a protein binding site

Can have consequences, but not always

Question 22

What types of drugs are stored in fat?

Answer 22

Lipid soluble drugs

Poor blood supply to fat tissue

Question 23

What types of drugs are stored in bone?

Answer 23

Calcium-binding drugs (e.g. tetracyclines)

Metals (e.g. lead)

Question 24

How does redistribution affect the pharmacological activity of drugs?

Answer 24

Can terminate pharmacological action of drugs

Initial distribution depends on blood flow to a body region