Pharmakinetics

Question 1

Routes of administration (5)

Answer 1

IV - directly into blood

Inhalation/smoking - absorbed into lungs

Intranasal/snorting - direct access to CSF

Oral - stomach –> intestine –> liver (can be absorbed through stomach)

IM

Question 2

Absorption (and lipid soluble)

Answer 2

Cell membranes are complex lipids

Only lipid soluble substance can passively diffuse easily through membrane

The more lipid soluble a substance, the more potent the substance to prod use a psychoactive effect.

Drugs differ in their lipid solubility depending:

1) how alkaline or acidic the drug
2) alkalinity or acidity of solution the drug interacts with.

Ex weak acid drug (aspirin) + strong acidic solution (stomach) = neutral charge (non ionized = lipid soluble = passes blood brain barrier

Question 3

Binding (and inactive binding)

Answer 3

Drugs will either bind to blood plasma and travel to target neurons or it will bind to inactive sites (depot binding) Differs for individuals.

Drugs that bind to inactive sites reduces the initial concentration of the drug available to produce a psychoactive effect (brain effect)

Inactive binding is only temporary and eventually the drug will return to blood stream (but the concentration is low).

Question 4

Inactivation (and enzymes)
     3 types (IIC)

Answer 4

Enzyme responsible for breaking down psychoactive substances
(found in liver, stomach)

Enzyme induction

• the more you take the drug the strong the enzymes becomes and more likely drug will be broken down.
• mechanism of tolerance
• produces cross-tolerance (smoking & antidepressants)

Enzyme Inhibition

• the more you take a drug, the more likely the enzyme will not break down the drug.
• mechanism of sensitization
• produces cross-sensitization (grapefruit & certain medications)

Enzyme competition

• two different drugs will compete for enzyme
• lead to elevated level of one drug (alcohol & valium)

Question 5

Tolerance

Answer 5

After repeated use you need more drug to produce same effect as first time

Question 6

Sensitization

Answer 6

After repeated use you become more sensitive to drug effect and need less to produce same effect

Question 7

Cross-tolerance

Answer 7

tolerance one develops for a drug will extend to another substance that is of a similar class

Question 8

Excretion (first and zero)

Answer 8

First order Kinetics:
- period of time for 50% of drugs to be removed
- longer time period/longer half life means the drug remains in the system longer and can increase abuse potential
- Relevant because:
     -methamphetamine has 
      stronger half life than 
      cocaine and 
      amphetamine
     - half life important 
      because less sever 
      withdrawal effects and 
       don't have to take 
       substance often.

HALF LIFE IMPORTANT because it impacts the degree of withdrawal

Zero-Order Kinetics:
- the rate of breakdown and excretion is constant regardless of the amount of substance. ex. the more you drink the longer it will take to leave the system.