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Pharmacology 1 > Pharmacokinetics > Flashcards

Pharmacokinetics Flashcards

1
Q

What are pharmacokinetics what do they effect

A

what the body does to a drug,determine the onset, intensity, and duration of drug action

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2
Q

What are ADME

A

Absorption: First, absorption from the site of administration permits entry of the drug
(either directly or indirectly) into plasma.

Distribution: Second, the drug may reversibly leave the bloodstream and distribute
into the interstitial and intracellular fluids.

Metabolism: Third, the drug may be biotransformed through metabolism by the liver or
other tissues.

Elimination: Finally, the drug and its metabolites are eliminated from the body in urine,
bile, or feces

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3
Q

What does understanding ADME help us with

A

Clinicians can design optimal drug
regimens, including the route of administration, dose, frequency, and duration of
treatment. (Optimizing the treatment)

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4
Q

How is the route of administration determined

A

By the physical properties and therapeutic objects

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5
Q

What is the parenteral route

A

Parenteral= away from the GIT and it includes IV,IM,SC

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6
Q

What are the advantages for the oral route

A

Oral drugs are easily self-administered,
and toxicities and/or overdose of oral drugs may be overcome with antidotes, such as
activated charcoal.

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7
Q

What are the disadvantages for the oral route

A

pathways involved in oral drug absorption are the most
complicated, and the low gastric pH inactivates some drugs, can’t be used while vomiting and diarrhea

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8
Q

How can we fight the low pH of the stomach

A

enteric-coated and extended-release preparations.

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9
Q

What are enteric coatings

A

chemical envelope that protects the drug from stomach acid,
delivering it instead to the less acidic intestine, where the coating dissolves and releases
the drug.

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10
Q

Give examples for E.C

A

omeprazole that is
acid labile, and for drugs that are irritating to the stomach, such as aspirin.

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11
Q

What are extended release coatings

A

have special coatings or
ingredients that control drug release, thereby allowing for slower absorption and
prolonged duration of action.

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12
Q

What are the abbreviations for extended release

A

ER, XR, XL, SR

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13
Q

What are the advantages for ER

A

can be dosed less frequently and may
improve patient compliance. In addition, ER formulations may maintain concentrations
within the therapeutic range over a longer duration, as opposed to immediate-release
dosage forms, which may result in larger peaks and troughs in plasma concentration

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14
Q

What are the other advantages for ER

A

advantageous for drugs with short half-lives. For example, the half-life
of oral morphine is 2 to 4 hours, and it must be administered six times daily to provide
continuous pain relief. However, only two doses are needed when extended-release
tablets are used.

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15
Q

Study the two tables, slide 6-7 from the notes

A

يلا يا قدع

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16
Q

What is absorption

A

transfer of a drug from the site of administration to the bloodstream.

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17
Q

What does the rate of absorption depends on

A

on the environment where the drug is
absorbed, chemical characteristics of the drug, and the route of administration

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18
Q

What are the mechanisms of absorption

A

Passive, facilitated,active, endocytosis

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19
Q

What is passive diffusion

A

the drug moves from an
area of high concentration to one of lower concentration. Passive diffusion does not
involve a carrier, is not saturable, and shows low structural specificity

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20
Q

How can the drugs penetrate the cell wall

A

Water-soluble drugs penetrate the cell
membrane through aqueous channels or pores, whereas lipid-soluble drugs readily move
across most biologic membranes due to solubility in the membrane lipid bilayers.

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21
Q

What is facilitated diffusion

A

entering the cell through specialized transmembrane carrier proteins that
facilitate the passage of large molecules.

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22
Q

Does facilitated diffusion need ATP, does it get saturated

A

It does not require energy, can be
saturated, and may be inhibited by compounds that compete for the carrier.

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23
Q

What is active transport

A

involves specific carrier proteins that span the membrane.
However, active transport is energy dependent

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24
Q

What is endocytosis

A

used to transport drugs of exceptionally large size across the
cell membrane.Vitamin B is transported across the gut wall by
endocytosis,

But exocytosis is the reverse of
endocytosis. Many cells use exocytosis to secrete substances out of the cell whereas certain neurotransmitters (for example, norepinephrine) are stored
in intracellular vesicles in the nerve terminal and released by exocytosis.

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25
How does the pH effect the absorption
A drug passes through membranes more readily if it is uncharged , therefore weak acids drugs are better in acidic conditions while weak bases are better in basic conditions
26
How does the blood flow affect absorption
The intestines receive much more blood flow than does the stomach, so absorption from the intestine is favored over the stomach.
27
How does the surface area affects absorption
With a surface rich in brush borders containing microvilli, the intestine has a surface area about 1000-fold that of the stomach, making absorption of the drug across the intestine more efficient.
28
Why is the drug not absorbed well during severe diarrhea
Because the drug drug moves through the GI tract very quickly
29
Why is the drug slowly absorbed after a meal
The presence of food in the stomach both dilutes the drug and slows gastric emptying. Therefore, a drug taken with a meal is generally absorbed more slowly
30
What is p-glycoprotein
transmembrane transporter protein responsible for transporting various molecules, including drugs, across cell membranes
31
Where can we find p-glycoprotein
the liver, kidneys, placenta, intestines, and brain capillaries,
32
Does it increases or decreases absorption and why
P-glycoprotein reduces drug absorption. If “pumps” drugs out of cells.
33
P-glycoprotein is associated with multidrug resistance
Yes
34
What is bioavailability
the rate and extent to which an administered drug reaches the systemic circulation.
35
How do we determine bioavailability
comparing plasma levels of a drug after a particular route of administration (for example, oral administration) with levels achieved by IV administration.
36
What determines/influence bioavailability
First pass,solubility, chemical instability, nature of the drug formulation
37
What is first pass hepatic metabolism
If the drug is rapidly metabolized in the liver or gut wall during this initial passage (it enters the portal circulation before entering the systemic circulation), the amount of unchanged drug entering the systemic circulation is decreased.
38
How do we combat first pass hepatic metabolism
Drugs with high first-pass metabolism should be given in doses sufficient to ensure that enough active drug reaches the desired site of action.
39
Give an example for a drug that goes under first pass hepatic metabolism
more than 90% of nitroglycerin is cleared during first-pass metabolism. Hence, it is primarily administered via the sublingual, transdermal, or intravenous route.]
40
How does chemical instability effect bioavailability
Some drugs, such as penicillin G, are unstable in the pH of gastric contents. Others, such as insulin, are destroyed in the GI tract by degradative enzymes
41
How does the nature of the drug formulation effects the bioavailability
particle size, salt form, crystal polymorphism, enteric coatings, and the presence of excipients can influence the ease of dissolution and, therefore, alter the rate of absorption.
42
What is bioequivalence
Two drug formulations are bioequivalent if they show comparable bioavailability and similar times to achieve peak blood concentrations
43
What are therapeutic equivalence
they are pharmaceutically equivalent with similar clinical and safety profiles.
44
Remember
therapeutic equivalence requires that drug products are bioequivalent and pharmaceutically equivalent.
45
What is drug distribution?
the process by which a drug reversibly leaves the bloodstream and enters the extracellular fluid and tissues.
46
What does drug distribution depends on?
Blood flow, capillary permeability, binding to the plasma proteins, lipophilicity
47
How does the blood flow effects distribution
It explains the short or long duration of the drugs, علاقة طردية
48
What organs get more blood flow than others
“vessel-rich organs” (brain, liver, and kidney)
49
Is the blood flow In the skeletal, adipose, skin and viscera higher or lower
Lower
50
What determines the capillary permeability?
by capillary structure and by the chemical nature of the drug.
51
How can the capillaries vary in the structure
the fraction of the basement membrane exposed by slit junctions between endothelial cells.
52
What's the difference between brain capillaries and liver ones
the liver and spleen, a significant portion of the basement membrane is exposed due to large, discontinuous capillaries through which large plasma proteins can pass. In the brain, the capillary structure is continuous, and there are no slit junctions
53
How can the drug enter the brain
drugs must pass through the endothelial cells of the CNS ( highly lipophilic and unionised) capillaries or undergo active transport.
54
How does the reversible drug binding to the protein effect the diffusion
It slows down the diffusion giving the drug a prolonged effect
55
Which plasma proteins is the major drug binding protein
lipids, proteins, or nucleic acids such as albumin
56
Can drug binding to the protein act as a reservoir
Yes, since it's reversible it will slowly re-release the drug
57
Why do drugs accumulate in the tissues
Drugs may accumulate because of binding to lipids, proteins, or nucleic acids. Drugs may also undergo active transport into tissues
58
What's the effect of the conc of the drug binding to proteins and extracellular fluids compared to the tissuees
The conc will be lowered in the blood
59
How do lipophilicity effect drugs
Lipophilicity increases the penetration of the cell membrane therefore it increases the distribution
60
What is the volume of distribution VD
defined as the fluid volume that is required to contain the entire drug in the body at the same concentration measured in the plasma
61
Describe the drug distribution in the plasma compartment
Has a low VD (4L/70-kg) High molecular weight Very high protein binding Trapped within the vascular compartment because it can't go through the slit junction Examples heparin
62
Describe the drug distribution in the extracellular fluid
Low molecular weight Hydrophilic Can pass through slit junctions of the endothelial tissues 14L/70kg Example amino glycosides
63
Describe the the drug distribution in the total body water
Low molecular weight Lipophilic Can move through the slit junction and cell membrane 42L/70kg Example Ethanol
64
What are the major routes of drug elimination
Hepatic, biliary, urinary They reduce the drug conc in the blood
65
Why can't the kidney efficiently excrete lipophilic drugs
readily cross cell membranes and are reabsorbed in the distal convoluted tubules
66
How can we help the liver to excrete lipophilic drugs
lipid-soluble agents are first metabolized into more polar (hydrophilic) substances in the liver via two general sets of reactions, called phase I and phase II
67
What is phase 1 metabolism
convert lipophilic drugs into more polar molecules by introducing or unmasking a polar functional group, such as –OH or –NH2. Phase I reactions usually involve reduction, oxidation, or hydrolysis. Phase I metabolism may increase, decrease, or have no effect on pharmacologic activity.
68
What effects the p450
Genetic variation, inducer drugs , inhibitor drugs
69
How does genetic variation effects the p450
Variations in P450 activity may alter drug efficacy and the risk of adverse events, example some individuals obtain no benefit from the opioid analgesic codeine, because they lack the CYP2D6 enzyme that activates the drug.
70
Give another example on genetic variation
clopidogrel ( a pro drug) carries a warning that patients who are CYP2C19 “poor metabolizers” have a diminished antiplatelet effect when taking this drug and an alternative medication should be considered
71
What are cyp inducers
Certain drugs (for example, phenobarbital, rifampin, and carbamazepine) are capable of inducing CYP isozymes. This results in increased biotransformation of drugs and can lead to significant decreases in plasma concentrations of drugs metabolized by these CYP isozymes, often with concurrent loss of pharmacologic effect
72
Name the problem with using rifampin for TB and HIV patients
significantly decreases the plasma concentrations of human immunodeficiency virus (HIV) protease inhibitors, thereby diminishing the ability to suppress HIV replication.
73
What are the cyp inhibitors
Inhibition of drug metabolism can lead to significant increases in plasma drug concentration and resultant adverse effects or drug toxicity
74
Name same examples for cyp inhibitors
Numerous drugs inhibit one or more of the CYP-dependent biotransformation pathways of warfarin. For example, omeprazole is a potent inhibitor of three CYP isozymes involved in warfarin metabolism
75
Name some natural substances that acts as inhibitors
Grapefruit juice, inhibits cyp3a4 and can be toxic with, nifedipine, clathromycin, simvastatin
76
What is phase 2 metabolism
This phase consists of conjugation reaction.A subsequent conjugation reaction with an endogenous substrate, such as glucuronic acid, sulfuric acid, acetic acid, or an amino acid, results in polar, usually more water-soluble compounds that are often therapeutically inactive
77
Talk about the drug clearance through the kidney
Drugs must be sufficiently polar to be eliminated from the body,Removal of drugs from the body occurs via a number of routes; the most important is elimination through the kidney into the urine.
78
What happens during glomerular filtration
Drugs enter the kidney through renal arteries.Free drug (not bound to albumin) flows through the capillary slits into the Bowman space as part of the glomerular filtrate.Lipid solubility and pH do not influence the passage of drugs into the glomerular filtrate. However, variations in GFR and protein binding of drugs do affect this process.
79
What happens in the proximal tubular secretion
Secretion primarily occurs in the proximal tubules by two energy￾requiring active transport systems: one for anions and one for cations.Each of these transport systems shows low specificity and can transport many compounds. Thus, competition between drugs for these carriers can occur within each transport system.
80
What happens during distal tubular reabsorption
As a drug moves toward the distal convoluted tubule, its concentration increases and exceeds that of the perivascular space. The drug, if uncharged, may diffuse out of the nephric lumen, back into the systemic circulation
81
How can we increase the clearance through distal tubular reabsorption
Manipulating the urine pH to increase the fraction of ionized drug in the lumen may be done to minimize the amount of back diffusion and increase the clearance of an undesirable drug
82
What is ion trapping
weak acids can be eliminated by alkalinization of the urine, whereas elimination of weak bases may be increased by acidification of the urine example, over dose by phenobarbital
83
Name some other routes for clearance
the intestines, bile, lungs, and breast milk
84
How can drugs be cleared through the skin, bile and milk
Drugs that are not absorbed after oral administration or drugs that are secreted directly into the intestines or into bile are excreted in the feces. The lungs are primarily involved in the elimination of anesthetic gases. Elimination of drugs in breast milk may expose the breast-feeding infant to medications and/or metabolites being taken by the mother and is a potential source of undesirable side effects to the infant.
85
What is the total body clearance
is the sum of all clearances from the drug￾metabolizing and drug-eliminating organs
86
What is half life
The time required to clear 50% of the drug
87
Name some clinical situations resulting in changes in drug half life
1) diminished renal or hepatic blood flow, for example, in cardiogenic shock, heart failure, or hemorrhage; 2) decreased ability to extract drug from plasma, for example, in renal disease 3) decreased metabolism, for example, when a concomitant drug inhibits metabolism or in hepatic insufficiency, as with cirrhosis
88
How can we decrease the half life of the drug
1 increasing hepatic blood flow 2 decrease protein binding 3 increase metabolism
89
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Pharmacology 1 (10 decks)

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