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Pharmacology > 3- Pharmacokinetics > Flashcards

3- Pharmacokinetics Flashcards

1
Q

What is enteral administration of a drug?

A

administration by mouth

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2
Q

What are some issues with enteral administration?

A

Simplest route, but exposes drug to hash acidic and basic environments that could limit its absorption

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3
Q

What is paraenteral administration of a drug?

A

drugs introduced directly across the body’s barrier defenses into the systemic circulation, immediately overcoming barriers that can limit the effectiveness of orally administered drugs

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4
Q

What is mucous membrane administration of a drug?

A

administration of drugs across mucous membranes

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5
Q

What are some benefits to mucous membrane administration of a drug?

A

provides rapid absorption, low incidence of infection, convenience and avoidance of harsh GI environments and first pass metabolism

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6
Q

What is transdermal administration of a drug?

A

passive diffusion across the skin directly into the blood

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7
Q

What type of drugs are ideal for transdermal administration?

A

Ideal for a drug that must be slowly and continuously administered over extended periods

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8
Q

What is the main barrier of transport for the drug into the cell?

A

The hydrophobic core of the cell membrane is the major barrier to drug transport

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9
Q

What types of drugs can overcome the nonpolar core of the plasma membrane to enter the cell?

A

Hydrophobic drugs like steroids.

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10
Q

What are the proteins called that can transport hydrophilic drugs across the plasma membrane?

A

OATs (organic anion transporter)

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11
Q

What is another method of entry for hydrophilic molecules to enter the cell?

A

Endocytosis

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12
Q

What is Fick’s law/equation?

A
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13
Q

What is the absorbtion of a drug?

A

How and how much of a drug gets into the blood stream. Blood level is important and related to the dose

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14
Q

What is the distribution of the drug?

A

How and how much of drug gets to a site of action and across barriers. It is the transport of absorbed drugs from plasma to tissues

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15
Q

What is the metabolism of the drug?

A

The degradation of drugs to an inactive form or the activation of prodrugs

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16
Q

What is the elimination of the drug?

A

The removal of drugs via urine, feces, expired air, breast milk, saliva or sweat.

Excretion of free unaltered drug is more difficult than metabolized drug

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17
Q

What is the bioavailability of the drug?

A

the amount of a drug available to the target organ or tissue

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18
Q

What are the factors that contribute to bioavailability?

A

The route that a drug is administered, the chemical form of the drug and a number of patient-specific factors such as GI and hepatic transporters and enzymes, combine to determine a drugs bioavailability

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19
Q

What is the equation of bioavailability?

A

Bioavailability (f) = (quantity of drug reaching the systemic circulation)/(quantity of drug administered)

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20
Q

When is the bioavailability = 1?

A

When the drug is not given oral, through yer butt or respiratory because it will bypass the liver for detox.

Since it doesn’t get metabolized in the liver, 100% of the administered drug will be in the systemic circulation.

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21
Q

What occurs if you have a higher and/or rapidly administered dose?

A

It results in a greater increase in local drug concentration, which in turn leads to more drug diffusion across the cell membranes or into the blood

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22
Q

Why is it good to administer a drug in a highly perfused compartment?

A

in a highly perfused compartment, drug molecules crossing into a compartment are rapidly removed, which in turn keeps the drug concentration low in that compartment

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23
Q

Why must you conisder budy size when deciding what dose to give the patient?

A

Patients with greater body mass have both an increased surface area and a larger tissue volume, which allows more area for diffusion to occur and thus increase absorption

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24
Q

Why can the brain only receive lipid soluble or low molecular weight drugs?

A

because though it’s a highly perfused organ, it is protected from drugs by the BBB

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25
Q

What is special about the circulation to the testes?

A

extra barrier called the blood-testes barrier that limits circulation of drugs to the testes

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26
Q

Where is the first pass extraction located?

A

The liver

27
Q

What is special about the kidneys when talking about drug metabolism?

A

highly perfused organ receiving about 25% of total cardiac output. Site of metabolism and excretion of a large number of drugs which could accumulate in the body in case of renal diseases

28
Q

What is special about the adipose tissues and bone for drug distribution?

A

poorly perfused tissues that have a slow accumulation of drugs. They are a reservoir for fat-soluble drugs like barbiturates and some opiates

29
Q

What is the most abundant plasma protein for drug binding?

A

Albumin

30
Q

What are the effects of drug binding to plasma proteins on availability?

A

Binding reduces the availability of a drug to diffuse into its target organ because only free or unbound drug is capable of diffusion across membranes

31
Q

What are the effects of 2 drugs if they compete for plasma binding proteins?

A

If 2 drugs are administered they could be competitive for blood protein binding and could increase the bioavailability of either of them. This could cause toxic effects.

32
Q

What is the major organ of drug metabolism?

A

Liver

33
Q

What type of reactions occurs in Phase I reactions?

A

Oxidation/reduction reactions

34
Q

Which enzyme mediates most of the Phase I reactions?

A

Cytochrome P450

35
Q

What might get added to a drug in a phase I reaction?

A

an -OH group

or an -NH2 or a -SH (basically anything that makes it polar)

36
Q

Though chemically modifying a drug can make it inactive, what can a Phase 1 reaction do to a prodrug?

A

Activate it

37
Q

What type of reactions occurs in Phase II reactions?

A

Conjunction/hydrolysis reactions

this hydrolyzes or conjugates a drug to a large polar molecule in order to inactivate it, or enhance its solubility for excretion

38
Q

What are the most commonly added groups in Phase II reactions?

A

glucuronate, acetate, glutathione and sulfate

(GAGS)

39
Q

What are phase III reactions?

A

they are specialized transporters that recognize the conjugates and expel them out of the cell

40
Q

What changed in the kidney causes an increased renal excretion for the drug?

A

Increasing blood flow, glomerular filtration rate and decreasing plasma protein binding all cause a drug to be excreted more rapidly

41
Q

What is biliary excretion?

A

drugs are secreted from the liver into the bile by members of the ATP binding cassette (ABC) superfamily of transporters

42
Q

What is the clearance of a drug?

A

Cl = (rate of elimination mg/min)/(concentration of drug mg/ml) = mL/min

It’s basically the volume of plasma that is cleared of the drug per unit time

43
Q

What is the 1/2 life (t1/2) equation for a drug?

A

t1/2 = (0.693 x Vd)/Cl

44
Q

What is the volume of distribution equation?

A

Vd = (dose mg)/(plasma conc. mg/mL) = mL

45
Q

What is the loading dose (generally)?

A

A single large dose used to achieve therapeutic level (Steady state concentration) quickly rather than using repeated small doses.

46
Q

What is the loading dose equation?

A

LD = Vd x Css
F

47
Q

What is the maintenance dose equation?

A

MD = Cl x Css x interval

48
Q

What is the steady state (Css)?

A

When clearance and the rate of administration of a drug are equal = steady state.

The amount of drug in the plasma will stay constant. As the drug is cleared it is equally administered and will distribute throughout the body.

49
Q

What is the equation for Css?

A

Dosing rate = Clearance x (Css)

which can be rearranged to…..

Css (mg/ml) = infusion rate (mg/min)
Clearance (ml/min)

50
Q

What is the extraction ratio?

A

Extraction = (Cin - Cout)/(Cin)

51
Q

What is pH trapping?

A

pH trapping is when drug is trapped on one side of the membrane due to charge

52
Q

Which form of the acid is able to cross the lipid bilayer?

A

The protonated form

53
Q

Which form of a base will be able to cross the plasma membrane?

A

The weak base (s) form of B

BH+(aq) <–> B(s) + H+(aq)

54
Q

What is the Henderson Hasselbalch equation for pH and pKa?

A

Predicts how much of a drug (weak acid or base) would exist in the protonated versus non protonated form at a given pH

55
Q

The Henderson Hasselbalch equation can be rearranged to which form to show protonated vs nonprotonated from?

A
56
Q

What fraction of acetaminophen would be in its protonated form in the stomach following an oral dose?

Acetaminophen is a weak acid with a pKa = 9.5, and stomach pH is approx. 2.5

A

log [HA] = 9.5 – 2.5 = 7
[A-]

log _[HA] _ = 7 = log _[10000000] _
[A-] [1]

So, [HA]/[A-] = [10000000]/[1]
[HA] = 10000000
[A-] = 1
Total = 10000001
% protonated = 10000000/10000001 ≈ 99.99%

57
Q

Generally, if the pKa is > the pH of the environment, which form (prontonated or non-protonated) will the drug be in?

A

Protonated

58
Q

What is 0 order kinetics?

A

Clearance rate remains constant despite increasing plasma drug levels.

This can cause dangerously elevated plasma concentrations of the drug that can cause toxic effects.

59
Q

What is 1st order kinetics?

A
60
Q

Which order (0 or 1) can use the half life equation?

A

1st order

61
Q

What is clearance (definition)?

A

Clearance is the rate of elimination of a drug from the body relative to the concentration of the drug in plasma.

62
Q

What is the acid dissociation constant?

A

Kd = [H]*[A]/[HA]

63
Q

What is the relationship between pKa and Ka?

A

pKa = -log(Ka)

Pharmacology (9 decks)

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