Pharmacokinetics Flashcards
(32 cards)
Define Pharmacokinetics
What the body does to drugs - lifecycle of drug in the body
Study of [ ] of drug in body over time
The movement and fate of drugs in the body (dosing regimens & absorption, dist. Metabolism, and excretion)
What are the routes of drug administration?
Best way to get drugs to CV system (super highway) - a drug is ‘in’ the body once its in the blood
1. Enteral route
Mouth to anus - GI tract (oral, sublingual, anus)
2. Parenteral Route
Not GI tract (Injections, drug devices IUD, Inhalation [local or systemic], topical[local], transdermal[systemic])
What are factors to consider in drug administration?
1. Drug characteristics - size, water vs lipid solubility, charge, pH stability)
2. Patient characteristics - age, consciousness, ability to follow instructions
3. Therapeutic objectives- urgency, local or systemic
Outline the ADME process
ABSORBTION(how does drug get absorbed=in the blood)
DISTRUBUTION (How does CV system move it around)
METABOLISM (What happens to the drug in the body - forms etc)
EXCRETION (How does the drug get out of the body)
What is absorbtion and what effects it?
Movement of drug from site of admin into blood (mostly passive diffusion)
Crosses 1 or more lipid membrane and influenced by
(1) [] gradient (2) Size (3) Lipid solubility
What does the charge of a drug do?
A drugs charge affects its lipid solubility and membrane permeability
What happens to an uncharged drug?
hydrophobic - passively diffuse across lipid bilayer ABSORBTION
What are different words for uncharged?
uncharged
unionized
non-polar
hydrophobic
lipid soluble
Lipophilic
What happens to a charged drug?
It is hydrophilic, water permeable, EXCRETION
What is another word for charged?
charged
ionized
polar
hydrophilic
water soluble
How do drugs exist in EQ?
Drugs are given as weak acid/weak base and exist in EQ in pronated and unpronated forms, Both EQ of HA+A- or BH+ + B = 100%
What is the EQ of a weak acid drug?
(Pronated) HA <-> A- + H+ (unpronated)
weak acid will be absorbed in acidic environment and excreted in basic environment
What is the EQ of a weak base drug?
(pronated) BH+ <–> B + H+ (unpronated)
weak base will be absorbed in basic envornment and excreted in acidic environment
What will happen to a drug in a acidic environment?
In an acidic environment (high H+ concentration; low pH) the equilibrium will shift to favour greater amounts of the protonated HA (absorption) and BH+ (excretion) forms. (proenated)
What will happen to a drug in a basic environment?
In a basic environment (low H+ concentration; high pH) the equilibrium will shift to favour greater amounts of the unprotonated A‐ (excretion) and B (absorbtion) forms. (unpronated)
What is Bioavailability?
Bioavailability (F)
The fraction of drug that reaches system (amount of drug in systemic circ/dose), IV = 100% bioavailability, each drug has unique bioavailability.
What is is distrubution and what effects it?
The process by which the drug reversibly leaves the bloodstream (b/w body compartments and sites of action - receptors), not effected by route of admin
Influenced by:
1) [] gradient
2) Size
3) Lipid solubility
4) Blood flow
5) Protein Binding (different than A)
How does blood flow inform drug dist?
Delivered in order of perfusion, 1st brain, heart, liver, kidneys, 2nd muscle, skin 3rd fat
How is dist effected by protein binding?
Drugs reversibly bind to proteins to varying degrees ( protein + drug <-> drug-protein complex (pharmacologically inactive), therefore lower [free drug], lower the therapeutic effect or [higher blood protein bound drug], lower pharm effects.
Pregnancy can change normal proteins and binding.
Describe how a drug’s distributional characteristics may be affected by pregnancy and what approaches should be taken
1) The placenta is not a barrier to drug transport (small, lipophilic, unionized drugs can passively diffuse)
2) Changes in Body Composition - (increase blood volume 40-50 %, increase body fat, plasma protein decreases (means less proteins to bind to therefore more free drug therefore higher potency?)
Approaches: (1) Rx cautiously,(2) therapeutic drug monitoring, (3) report Vd as Vd/kg to adjust for weight
Volumes associated w different body fluid compartments?
70 kg person for hydrophilic drugs
42 L Total Body Water
2/3 ICF - 28 L
1/3 ECF - 14 L
}} 0.8 Intersitial Fluid (11 L)
}}0.2 Plasma (3L)
What is the deal with volume distribution?
[concentration of drug in blood] = dose/volume distribution
Not a real physiological # but rather a proportinality constant that relates the amount of drug in the body to it’s concentration in the blood.
Large (>42 L) - drug dist. Outside of the body flids into the tissues/fats (tissue binding)
Small (<=) drug has limited dist. (plasma binding)
What is drug metabolism?
The biotransformation of parent drug to metabolite. Converting a original drug to metabolite to make drug more polar and therefore renally excreted.
Occurs in liver VIA 2 enzyme catalyzed processes:
Desrcribe Phase 1 metabolism
Phase 1 (oxidation/reduction/hydrolysis) - becomes inactive
P450 family of related enzymes (different enzymes metabolize specific drugs)
Ex, acetaminophen is metabolized by CP1A2, CP3A4, CP2E1
Add new or uncover existing polar chemical groups to increase water solubility (-OH, -COOH, -NH2, SH)
The activity can be induced or inhibited by other drugs, food, pregnancy, disease
