Pharmacokinetics Flashcards
1
Q
Pharmacokinetics
A
Study of how the body physically handles and moves a drug
- Absorption
- Distribution
- Metabolism
- Excretion
2
Q
Absorption
A
- Passage of drugs from outside the body into the blood and tissues/cells
(duodenum is where it takes place) - The ability to cross membranes is important since most drugs exert their action in the cells of the body rather than within the blood
- Solubility
~ Drugs must be water and fat soluble
for absorption to take place
> Water soluble: dissolves in the GI
tract; in solution within the blood
> Fat soluble: crosses membranes
easily
• Important because most
membranes are made of lipids
* Between GI tract and
Blood - Capillary wall
* Between blood/
Intracellular Fluid/Cell -
Capillary wall/cell
membrane
* Into cells
* Between cell structures
3
Q
Mechanisms of Membrane Crossing: Passive Diffusion (most common)
A
- Driven by a concentration gradient
~ Area of high concentration on one
side of the membrane and an area of
low concentration on the other - The more fat soluble the drug the easier the transport, but the main driving factor is the concentration gradient
4
Q
Mechanisms of Membrane Crossing: Active Transport
A
- Drug attaches to a protein embedded in the lipid membrane
- Protein transports the drug across the membrane
~ Requires energy
~ Fairly specific
~ Transports one way
~ Can move against a concentration
gradient - Transports chemicals against gradient
- One of the ways chemicals get to the brain
5
Q
Mechanisms of Membrane Crossing: Facilitated Diffusion
A
- Driven by a concentration gradient, but a protein pathway is required for passage
- Similar specificity seen in active transport
- Does not require energy
- Moves through special pathways but still requires a gradient
6
Q
Drugs Crossing Capillaries
A
- All drugs will eventually pass through the capillary walls and move into the tissues
~ Those more fat soluble will pass easier
~ Those more water soluble will utilize
gaps between the endothelial cells of
the capillaries - All chemicals need some sort of fatty or water solubility (fatty=easier)
7
Q
Blood Brain Barrier
A
- CNS capillaries don’t have the typical endothelial capillary gaps
- Drugs that are more fat soluble penetrate the CNS capillaries easier
- Water soluble require special transport systems to the CNS (active transport)
- The BBB prevents (makes it harder) bad thins from entering the brain
8
Q
Administration
A
How the drug is put in contact with the body
- Oral
- Sublingual (under tongue)
- Buccal (between cheek and gums)
- Rectal
- Parental (injected)
- Topical (skin or eyedrops)
- Inhalation
9
Q
Oral Administration
A
Drug is swallowed
- Used when either systemic effects or local GI tract effects are desired
- Most popular route:
~ Cheapest
~ Most convenient
~ Safe
10
Q
Oral Administration Limitations
A
- Stomach acid and intestinal enzymes can inactivate some drugs
- Some molecules are too large for GI tract absorption
- Absorption takes longer than parenteral routes
11
Q
Oral Administration GI Tract Absorption
A
- Drugs must be both water and fat soluble
~ Drugs must be water soluble to be in
solution before it’s absorbed
> Drinking water with drug
administration can speed
absorption
> Drugs already in solution are
absorbed faster
~ Drugs must be fat soluble to cross
the membrane/vessel wall into the
blood - Occurs in the duodenum of the small intestine via passive diffusion
12
Q
Sublingual/Buccal Administration
A
- Sublingual: under the tongue
- Buccal: against cheek
- Tablets dissolve quickly allowing the drug to be absorbed into the blood supply of the mouth
- Drugs tend to be very potent to have an effect as only a small amount is absorbed
- Used when speedy absorption is required
13
Q
Rectal Absorption
A
- Drug administered as suppository composed of a substance that melts at body temperature
~ Drug absorbed by the circulatory
system
~ Used sometimes for those who can’t
use oral administration
14
Q
Parenteral Administration
A
- Drugs are injected
~ Intravenous
~ Intramuscular (have to cross memb.)
~ Subcutaneous (have to cross memb.) - Used when speed of absorption is a factor or drug can be altered by GI Tract
~ Intravenous is fastest followed by
intramuscular then subcutaneous
15
Q
Topical Administration
A
- Drugs applied to surface of
~ Skin
~ Eyes
~ Nose
~ Throat (spray) - Can have local or systemic effects
- Absorption depends on the area covered and the fat solubility of the drug
~ When applied to mucous membranes
absorption is faster
16
Q
Inhalation Administration
A
- Drugs are inhaled into the respiratory tract
~ Typically used to treat problems
locally
> Aerosols and dry powders are
typically used
~ Fast, but variable absorption takes
place via this route (human error) - Lungs are lined with blood vessels which makes it fast absorption
17
Q
Dosage Forms: Tablets
A
- Solid form
- Contains active ingredient and inactive ingredients
~ Inactive ingredients (make it easier to
swallow)
> Binders
> Bulk
> Slow release covering
> Chemical for break down in GI
tract
> Color
> Flavoring
18
Q
Dosage Forms: Capsule
A
Active and inactive ingredients contained in a gelatin container
19
Q
Dosage Forms: Liquids
A
- Syrup
~ Sweetened aqueous solution - Elixir
~ Sweetened ethanol and aqueous
solution - Suspension
~ Drugs that can’t be dissolved in water
suspended in another liquid - Emulsion
~ Drugs that are fat soluble dispersed in
water - Easier for kids to take
- All different in water content
- Already in solution so it’s easier to absorb
20
Q
Distribution
A
- Movement of the drug through the circulatory system to the target tissues
- Distribution is faster to those areas with greater blood flow
~ Liver
~ Kidney
~ Brain
21
Q
Volume of Distribution
A
- The amount of a drug that is distributed and bound to the tissues and free protein
~ The greater the volume of the
distribution the less drug available to
bind with target receptors - Drugs with a high volume of distribution require a higher dose
- Larger people especially those who are obese require a higher dose
22
Q
Metabolism
A
- Chemical alteration of a drug by enzymes mostly in the liver, kidneys, and intestines
- Drug interacts with enzymes and is converted to metabolites
~ Metabolites are typically inactivated,
more water-soluble forms of the
chemical - Liver, kidneys, and intestines work really hard to metabolize drugs
23
Q
Metabolism: First Pass Effect (oral only)
A
- Drugs that are administered orally are absorbed in the GI tract and are passed directly to the liver before the systemic circulation
~ Some amount of drug administered
this way is metabolized before
reaching the target tissues
> Must give higher doses of orally
administered drug due to this fact
24
Q
Bioavailability
A
- The degree to which a drug can access its site of action
~ A function of the body’s ability to
absorb and distribute a drug - Sources of reduced bioavailability
~ Incomplete dissolving in small
intestine
~ Breakdown by intestinal enzymes
~ First pass effect
~ Reduced rate of absorption in the
small intestine
~ Volume of distribution - Can the body absorb and distribute a drug? = drug is bioavailable
~ If not, the drug is useless
25
Q
Excretion
A
- Removal of the drug/metabolites from the body
~ Typically, through the renal or biliary
systems
> More water soluble via the kidney,
and more fat soluble via the liver
~ Lungs, sweat, saliva are other
possible routes, but minor
~ Most drugs are made more water
soluble through metabolism for renal
excretion - Main route: pee
26
Q
Half-Life
A
- The time required for the amount of drug in the blood to be reduced by one half
~ Function of metabolism and excretion
~ Drugs that have longer half-life values
have longer duration of action
> Drug can be administered fewer
times to maintain therapeutic
effects
27
Q
Effects of Exercise on Pharmacokinetics
A
- Oral absorption is slowed due to decreased rate of gastric emptying and decreased blood flow to the GI tract (bad)
- Blood flow to the liver and kidneys is decreased, increasing duration of drug action due to decreased metabolism and excretion rates (good; more bioavailable/longer half-life)
- Blood is needed elsewhere during exercise (muscles)
