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Exam 2 > Pharmacokinetics > Flashcards

Pharmacokinetics Flashcards

1
Q

What are the mechanisms of drug permeation?

A

Aqueous diffusion (par acellular pathway), lipid diffusion (transcellular pathway), special carrier, endo/exocytosis

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2
Q

Absorption

A

transfer of a drug from its site of administration to the blood stream

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3
Q

What is the level of absorption for IV drugs?

A

Complete, 100%, because the entire dose reaches the systemic circulation

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4
Q

Oral Route

A

Maximum convenience, but absorption may be slower and less complete than with other routes

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5
Q

First Pass Effect

A

Effect where ingested drugs are fractionally metabolized in the gut all and liver before reaching circulation

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6
Q

Sublingual

A

The drug enters systemic circulation directly from under the tongue. Drug bypasses the first pass effect. Enteral route

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7
Q

Rectal

A

There is a partial avoidance of the first pass effect. Enteral route

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8
Q

Parental Routes

A

IV, intramuscular, subcutaneous (below skin) and intradermal (in skin)

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9
Q

What is the solubility of nonionized molecules?

A

Liposoluble and can diffuse through the cell membrane

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10
Q

What is the solubility of ionized molecules?

A

Low liposolubility and have difficulty passing through the membrane

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11
Q

For weak acids, which form will permeate through the membranes?

A

The uncharged (protonated) form (HA)

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12
Q

What is permeating for weak bases?

A

The uncharged form (unprotanted) will permeate while the charges form will not

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13
Q

Conceptually, what does the Henderson Hasselbach Equation tell you?

A

Tells you that the ratio between unprotonated and protonated forms is based on pH and PK

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14
Q

Weak acids are excreted better in_________, weak bases are excreted faster in ___________.

A

Alkaline urine, acidic urine

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15
Q

According to the HH equation, when pH=PK

A

Unprotonated concentration=protonated concentration

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16
Q

For each unit of pH above the pK…

A

The unprotonated concentration will be ten time the protonated concentration

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17
Q

For each unit of pH below the PK….

A

The protonated concentration will be ten time the unprotonated concentration

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18
Q

Why does most drug absorption occur in the small intestine?

A

Because of its large surface area. Any factor that accelerated gastric emptying will increase the rate of drug absorption

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19
Q

How does blood flow affect absorption?

A

Increased blood flow will increase absorption

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20
Q

P-glycoprotein (MDR1)

A

Transporter protein responsible for transporting several drugs across cell membranes. Reduced drug absorption.

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21
Q

Bioavailability

A

Fraction of administered dose of a drug that reaches the systemic circulation

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22
Q

How do you determine bioavailability?

A

Compare the area under the curve of a particular route with the AUC after IV infection (should be 100%)

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23
Q

what factors can affect bioavailability?

A

Drug formulation, chemical instability, food and drug interactions, first pass metabolism, drug solubility, P-glycoprotein

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24
Q

Pharmaceutically Equivalent

A

Contain the same active ingredient and are identical in concentration, dosage form, and route of administration

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25
Q

Bio equivalent

A

When two pharmaceutically equivalent drugs have nearly superimposable concentration time plots

26
Q

What is the point of looking at bioequivalence?

A

If two drugs are bioequivalent, one can safely replace the other

27
Q

Drug Distribution

A

Process by which a drug leave the blood stream and enters the extracellular fluid or the cells of the tissues

28
Q

What determined drug distribution?

A

Blood flow, capillary permeability, tissue volume, drug binding, drug hydrophobicity

29
Q

Which parts of the body receive the drugs first/get most of the drugs?

A

Vessel rich groups that get lots of blood (brain, liver, kidney…) then it foes to the muscles

30
Q

What do acidic drugs bind to?

A

Plasma albumin

31
Q

What do basic drugs bind to?

A

Alpha1-acid glycoprotein

32
Q

What increases the risk of bilirubin encephalopathy?

A

Displacement of unconjugated bilirubin from albumin by sulfonamide drugs

33
Q

Warfarin and plasma protein concerns

A

Warfarin is highly bound to albumin and only a small fraction is free. Sulfonamide so will displace warfarin causing a significant increase in the plasma level of free warfarin—>increase bleeding

34
Q

What are the only drugs that can cross the blood-brain barrier?

A

Lipid soluble due to tight binding of zonula occludens

35
Q

Metabolism of Drugs

A

Most lipid soluble drugs are not easily excreted because they can be reabsorbed easily. They must undergo a biotransformation that will make them more polar and inactive metabolites which can be easily excreted

36
Q

What reactions are involved in drug metabolism?

A

Phase I and phase II reactions

37
Q

Phase I reactions:

A

Oxidations, reduction, decarboxylations, deamination, hydrolytic reactions. Usually result in polar, inactive metabolites

38
Q

Prodrugs

A

Pharmacologically inactive compounds that are designed to maximize the amount of active species that reaches the site of action

39
Q

Cyclophosphamide

A

Drug that is bio activated by metabolism to an active anticancer metabolite

40
Q

How are Prodrugs usually converted into active metabolites?

A

Through hydrolysis of an ester or amide linkage

41
Q

Phase II Reactions

A

Conjugation reactions that form a covalent bond between the drug molecule and something else (amino acid, sulfate, etc…)

42
Q

What is the main site of drug metabolism?

A

The liver

43
Q

Where are the enzyme systems for phase I reactions located?

A

The ER

44
Q

Where are the enzyme systems for phase II reactions located?

A

Cytosol

45
Q

What system catalyzes most phase I reactions?

A

CytochromeP450 system

46
Q

What are the three main xenobiotic receptors?

A

Aryl hydrocarbon receptor (AhR)
Pregnane X receptor (PXR)
Constitutive lay active receptor (CAR)

47
Q

Enzyme Induction

A

Drugs will bind to xenobiotic receptors which activates the receptor, allowing it to translocation to the nucleus and bind to the promotes of various enzymes

48
Q

What are the clinical consequences of enzyme induction?

A

A drug can increase its own metabolism, a drug can increase the metabolism of a coadministered drug (can reduce plasma concentrations below therapeutic levels)

49
Q

What drugs inhibit cytochromes P450?

A

Amidodarone, cimetidine, ketoconazole,erythromycin, chloramphenicol, grapefruit juice

50
Q

Macrolide Antibiotics

A

Inhibit P-glycoproteins which can lead to increased serum levels of drugs (e.g., digoxin) that are excreted by P-glycoprotein

51
Q

What else can transcriptionally regulate P-glycoprotein?

A

PXR

52
Q

What is the most common factor responsible for variations drug responses?

A

There is a genetic variation in enzymes that catalyze drug metabolism

53
Q

What does grapefruit juice inhibit?

A

CYP3A4 and P-glycoprotein in the small intestine

54
Q

What is the most common mechanism of drug excretion?

A

Renal excretion (a small number are excreted in the bile)

55
Q

Volume of distribution

A

A measure of the apparent space in the body available to contain the drug

56
Q

Clearance

A

Measure of the body’s ability to eliminate the drug

57
Q

Bioavailability

A

The fraction of the drug that is absorbed into the systemic circulation

58
Q

Volume of distribution formula

A

Vd=amount of drug in body/plasma drug concentration. Theoretical with no real life application.

59
Q

Maintenance Dose

A

Schedule of drug administration to maintain specific range of drug plasma concentration over a long period of time

60
Q

Loading Dose

A

Quick way to achieve a target plasma level

Exam 2 (10 decks)

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