Pharmacokinetics Distribution (Blood-Brain Barrier)

Pharmacokinetics Distribution (Blood-Brain Barrier)

1. the blood-brain barrier keeps toxins & poisons from reaching the brain.

2. only drug molecules that are lipophilic (able to cross) or that have a transport system

   can penetrate the barrier

Pharmacokinetics Distribution (placental barrier)

1. placental barrier separates maternal circulation from fetal circulation

2. in order to pass through placenta, drug must be lipophilic, not ionized, & not protein bound

Pharmacokinetics – Metabolism of drugs

1. occurs primarily in the liver

2. some metabolism occurs in other tissues, ie. gastrointestinal (GI) tract, lungs, kidney, & skin

3. when drugs are metabolized, they are changed from their original form to a new form

   sometimes referred to as "biotransformation"

   Pharmacokinetics – Metabolism Rates

   1. metabolism occurs at different rates for different drugs

   2. the percentage of drug that is metabolized each time the drug circulates or passes through the

   liver is the same, but the total number of drug molecules that are metabolized will be different

Pharmacokinetics – Metabolism first-pass effect (oral)

1. highly metabolized drugs may lose their therapeutic effectiveness quickly during their first pass through the liver (following oral administration), before they reach general circuation

2. This loss of effectiveness is called first-pass effectively

Pharmacokinetics: Excretion – the process of removing a drug or its metabolites from the body

routes for drug excretion:

1. urine (most common)

2. bile in the GI tract

3. expired air from lungs

4. breast milk

5. sweat from the skin (therapeutically not important)

6. saliva (therapeutically not important)

Pharmacokinetics: Excretion – three processes involved in renal excretion

1. glomerular filtration

2. passive tubular reabsorption

3. active tubular secretions

Pharmacokinetics: Excretion – half-life

1. the amount of time that is required to remove half (50%) of the blood concentration of a drug is called half-life

2. drugs have various half-lives measured in minutes or even days

3. in one half-life, a set percentage of the drug molecules present in the blood will be eliminated, not an absolute set number of drug molecules

Pharmacokinetics: Excretion – steady state

1. the full pharmacotherapeutic response of a particular drug dose is measured when the drug has achieved steady state

2. steady state is not based on drug dose or frequency of drug administration

Pharmacokinetics: Excretion – clearance (rate at which drug molecules disappear from circulatory system

major modes of clearance include:

1. renal excretion (kidney)

2. hepatic metabolism (liver)

gender of patient can alter the clearance of some drugs (affected by hormones, adipose in females etc)

Pharmacodynamics: the biological, chemical, and physiologic actions of a particular drug within the body and the study of how those actions occur