ADMET (EXAM 3) Flashcards
Identify the portions of a concentration vs. time curve that produce a pharmacologic effect
- onset (how quickly exhibits effect)
- reaches MEC - duration (how long it exhibits effect)
- remains above MEC - intensity (magnitude of pharmacologic)
- max conc. or when highest
Provide a route of administration, identify barriers that may reduce the amount of drug that reaches the site of action.
- tissue barriers (blood brain barriers)
- can go through the barrier it is going through first
- most require 1 or more passage for the drug to cross the systemic circulation
define disposition
the fate of a drug after it has entered the systemic circulation
define pharmacokinetics
study of absorption, distribution, biotransformation, and elimination of xenobiotics
define pharmacodynamics
the study of the molecular, biochemical, and physiological effects of xenobiotics and their mechanisms of actions
what percent of drugs currently fail in clinical trials due to problems with ADME?
<10%
what are the primary routes of administration?
- renal via kidney (most drugs)
- bile (feces)
Describe the four potential consequences of drug metabolism (biotransformation) as it relates to pharmacologic activity
- Active drug to inactive metabolite
- Active drug to active metabolite
- Inactive drug to active metabolite
- Active drug to reactive metabolite
what is the fastest route of admin?
IV
what is the slowest route of admin?
oral
a reduction in the extent of absorption will impact what effect?
intensity
a reduction in the speed of entry will impact what effect?
onset
mechanism of a drug to its effects
- drug given
- released
- particles in fluid
- dissolution
- drug in solution
- degradation –> tissues –> effect
- absorption
- liver
- excretion
- central compartment
- distribution
- tissues
- effect
Name the factors that determine drug absorption across the membrane.
- Characteristics of the membrane
- Mechanisms of passage across membranes
- Dwell time of drug-membrane interface
- Physicochemical characteristics of the drug
- pH of the microenvironment
- Surface area of absorptive surface
Identify the site in the GI tract where most drug absorption occurs.
small intestine
- SA is increased with folds
Identify the mechanism by which nanoparticles cross biological membranes.
endocytosis
what is FICK’s law of diffusion?
when it undergoes passive diffusion, the transport rate should increase as the concentration increases
in contrast to simple diffusion, carrier-mediated transport is ___
both saturable and subject to competitive inhibition
Differentiate the two forms of carrier-mediated absorption: facilitated diffusion and active transport.
a. facilitated diffusion
– With concentration gradient only
– Conformational change
– No energy and involves transport proteins
b. Active transport
– May go against gradient
– Needs energy
Describe the impact of efflux transporters on drug absorption from the small intestine.
- Efficiently remove drugs from cells that have entered via passive diffusion
- Can reduce the amount of drug that accumulates in certain tissues, such as brain
- Increases the amount of drug absorbed with pgp
- Can either move solutes in or facilitate their movement out of the cell
- in to out
what are the mechanisms by which drugs cross the biological membranes
transcellular, paracellular, carrier-mediated transport (facilitated diffusion and active transport)
what is transcellular diffusion
→ driven by conc. gradient
- 95% drugs absorbed here
- Can be increased by
1. Removing ionized groups
2. Increasing lipophilicity
3. Reducing size
- Compromise between solubility and permeability necessary
what is paracellular diffusion
→ driven by conc. gradient
- Tight junctions between cells
–> Small channels
–> MW <180 Da (polar mol.)
–> Very few drugs
–> Toxins can open junctions
–> Selective openings can active oral absorption of insulin and other proteins
describe the effects of drug distribution on the conc. vs. time curve
- Can be different for different people
- When in plasma it can be readily distributed and restricted to that area and be a declining linear line
- When in other areas it will move to other tissues as the plasma or other area is declining and make a small to big then decreasing curve
- A drug only distributed in the vascular space will exhibit mono exponential blood conc. Vs. time curve after IV admin
what is perfusion rate limited
Readily penetrates endothelial membrane so that the delivery rate of the drug to the tissue by perfusing blood is what determines how quickly a drug will appear in tissue
what is permeability rate limited
- Slowly passes across the endothelial membrane
- Drug is delivered to tissues more quickly than moving to the blood then tissues
what is convection
- Pressure is the driving force
- Use of large molecules such as MABs
what is diffusion
- Most drugs undergo here
- Uses concentration gradient as driving force of movement
how can differences in pH result in drug trapping of drugs
- When concentration of a drug within a tissues has pH differences that lead to ionization states of the drug to in the tissue environment
- The inability for ionized drug to cross membranes can be used to enhance urinary excretion of drugs by changing urine pH
how can plasma protein binding effects distribution and effect of drugs
- We want free drug as it can move back and forth
- Drugs that are bound to RBCs, proteins, etc. can’t pass the membrane
–>Blood brain barrier
–Tight junctions have no permeation
–Negative head groups limits diffusion for acids
– High conc. of Pgp leads to high efflux activity
what are the 4 mechanisms drugs can reach the CNS
- Appropriate physicochemical properties
- Utilize an existing transporter
- Disruption of BBB
- Direct administration into the CNS
what molecule or drug is best for pregnancy women
large polar molecules
what are the 3 barriers of drug entry in the brain
- Blood-Brain Barrier
- Blood-Arachnoid Barrier
- Blood-CSF Barrier
Name the primary routes by which drugs are excreted from the body.
kidney(renal), biliary (feces)
Identify the processes involved in renal excretion
filtraction, reabsorption, secretion
what are the anatomical location s of the processes involved in renal excretion
filtration
- glomerulus
secretion
- proximal convoluted tubule
reabsorption
- distal convoluted tubule
biotransformation
- kidney and liver (vitamin D)
what are the mechanisms of hepatic elimination
metabolism and biliary excretion
Plot the relationship between MW and renal clearance.
Decrease in CLr with inc in MW
Plot the relationship between dose and urinary excretion rate for a drug that undergoes filtration only and one eliminated primarily through renal excretion.
- With filtration only the excretion rate is an increase
–> Increase in CLR with inc. in creatinine clearance - With active tubular secretion it increases but then reaches a saturation point due to being a carrier-mediated process
Plot the relationship between MW and percent excreted in the bile.
As MW inc. Bile inc.
Describe the impact of enterohepatic recirculation on drug half-life in the body.
- EHR will increase the half-life because of it getting reabsorbed and continuing the process of reabsorption from the intestine
- If used with some bile binding agent the half-life will decrease because it is not reabsorbed
what is the first-pass effect of pre systemic circulation
all blood from stomach and small intestine flow to the portal veinal absorbed drug passes through the liver before entering the rest of the body. if drug is metabolized or excreted in bile unchanged, a significant fraction of the dose may be eliminated before entering the systemic circulation
what is the passage of drug from the blood to the liver
- from hepatic vein or artery from sinusoid
- out to in
- active transport
why are transporter proteins important
uptake and efflux from the blood and transport to bile
how does bile move
in to out
where does bile get collected
hepatic duct (canaliculi)
what is the passage from the liver to the intestine
- bile moves via hepatic duct to gall blader
- bile stored and concentrated in gall bladder
- bile released in intervals from gall bladder into intestine
what are the classes of agents
a,b,c
what is the enterohepatic cycles
small intestine –> portal vein –> liver –> bile duct
–> repeat
what is pulmonary excretion
any volatile compound that has potential for pulmonary excretion
- simple passive diffusion
what are other routes of excretion
hair, sweat and saliva, milk, tears