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CMD Block 2 > Pharmacokinetics > Flashcards

Pharmacokinetics Flashcards

1
Q

Clearance

A

CL = rate of elimination/concentration
CL = Q(Ca-Cv)/Ca = QE
Body’s efficiency of drug removal;
Volume of fluid from which the drug is removed per time

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2
Q

Volume of Distribution

A

Vd = amount of drug in the body/concentration in blood

Apparent space drug resides in

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3
Q

Elimination Half Life

A

Rate of drug removal

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4
Q

Bioavailability

A

Fraction of Drug Absorbed

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5
Q

Dosing Rate

A

= dose/T
= CL * Css
goal is to maintain steady state concentration

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6
Q

Plasma volume

A

4L

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7
Q

ECF volume

A

12L

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8
Q

TBW

A

40L

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9
Q

elimination constant, Ke

A

= CL/Vd = 0.7/(t1/2)

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10
Q

One compartment open model

A
  • single IV dose
  • assumes entire body is one compartment
  • assumes drug is distributed evenly
  • assumes open system (excretion)
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11
Q

Two compartment model

A
  • single IV dose
  • assumes most of drug is in a particular compartment
  • assumes equilibrium between blood and other areas
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12
Q

Multicompartment model

A
  • needs computer assistance
  • measures area under curve (AUC)
  • more widely used than other models
  • CL = dose/AUC
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13
Q

Predicted Css after various dosing schedules:

A

Css = (F * Dose)/(CL * T)

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14
Q

In a multiple IV bolus, time to steady state:

A
  • is about 5 half lives

- independent of dose or dose interval but dependent on t1/2 (plateau principle)

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15
Q

IV infusion, Css =

A

infusion rate/total body clearance

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16
Q

Loading dose

A
  • use it when you can’t wait for 5 half lives to achieve Css
  • LD = (Css * Vd)/F
  • but watch out for dangerously high volumes…
  • maintenance dose: Dosing rate = (target Css * CL)/F
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17
Q

What does it mean for a drug to have zero order kinetics?

A
  • Enzymes that metabolize the drug are saturated (are rate limiting) at normal drug levels in the body
  • Same amount of drug metabolized regardless of drug level in the body
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18
Q

Zero order kinetics drugs

A 
Ethanol
Heparin
Phenytoin
Aspirin
Amobarbital
Tetracycline
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19
Q

For zero order kinetics, LD =

A

(Css * Vd)/F

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20
Q

For zero order kinetics, Css =

A

(Km * DR) / (Vm - DR)

Km = dose that produces 50% of maximal elimination rate 
Vm = maximal rate of process
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21
Q

For zero order kinetics, DR =

A

(Css * (Vm - DR)) / Km

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22
Q

Pharmacokinetics

A

Concerned with the disposition of the drug in the body

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23
Q

Ways to modify drug absorption

A

delayed release
rapid release
transdermal
depot preparations

24
Q

Effect of stomach’s acidic environment on drug absorption

A

Acidic drugs will be nonionized and absorbed,

basic drugs will be ionized and won’t be absorbed until SI

25
Q

Drugs that reduce gastric emptying

A

anticholinergics
narcotics
analgesics

26
Q

Most rapid drug delivery route

A

IV

27
Q

Intrathecal route of delivery

A
  • injection into subarachnoid space
  • way to bypass BBB
  • good for local effects like spinal anesthesia, or acute CNS infix like meningitis
28
Q

Topical drug route

A
  • good for lipid soluble drugs that pass easily through epidermis
  • fentenyl, nicotine, nitroglycerine, birth control
29
Q

Factors affecting rate of drug distribution

A
  • cardiac output and regional blood flow
  • capillary permeability
  • tissue volume
30
Q

Factors affecting extent of drug distribution

A
  • membrane transport
  • permeability
  • plasma protein binding
  • intracellular binding
31
Q

Total blood flow is greatest to

A

brain
kidneys
liver
muscle

32
Q

Highest perfusion is to

A

brain
kidneys
liver
heart

33
Q

Two deviations from typical capillary structure that affect capillary permeability

A
  • kidneys: large spaces between endothelial cells so more extensive drug distribution via filtration
  • brain: BBB has tight junctions so polar substances do not readily pass
34
Q

Drug binding to plasma proteins

A
  • acidic drugs bind to albumin
  • basic drugs bind to globulin
  • nonspecific and reversible binding
  • slight changes in binding of drugs that are mostly bound result in huge clinical effect
35
Q

Cause of drug accumulation in tissues

A
  • active transport or binding
  • reversible and saturable
  • dep on: concentration, affinity, binding
36
Q

Drug reservoirs

A
  • stomach: traps basic drugs (Codeine)
  • Albumin: limits availability of free drug (Warfarin)
  • Tissues: liver concentrates quinicrine, thyroid concentrates iodine, bone concentrates divalent metal compounds/tetracycline/heavy metals
  • Fat: traps lipid soluble drugs, huge variability between patients
37
Q

Drug redistribution

A

is a mechanism for drug termination, often b/c differences in blood flow
- example is thiopental (anesthetic) that gets to brain quickly (also equalizing with plasma) but also accumulates in fat

38
Q

Drug distribution patterns

A
  1. remain in vascular system (dextran)
  2. uniformly distributed in TBW (ethanol)
  3. concentrated in tissues (iodine, tetracycline)
  4. non-uniform pattern most drugs
39
Q

Biotransformation

A
  • chemical modification of xenobiotics by endogenous enzymes

- reactions are enzymatic (follow MM)

40
Q

Michaelis Menton eqn

A

V = (Vmax * S)/ (Km + S)

41
Q

Phase I metabolic reactions

A
  • convert parent drug to inactive drug by adding or unmasking a functional group (-OH, -NH2, -SH)
  • if metabolite is polar enough, it can be excreted
  • product can be highly reactive and sometimes toxic (free radicals)
  • occur mostly in ER
  • oxidation, reduction, hydrolysis
42
Q

Phase 2 metabolic reactions

A
  • covalent addition of amino acids (glucuronic acid, glutathione, acetate, amino acids)
  • these covalent modifications are usually inactive and readily excreted (except 6-glucuronide
  • occur mostly in cytosol
  • glucuronidation, glutathione conjugation, sulfoxidation, acylation
  • usually make it more water soluble (except for acylation)
43
Q

Organ or TIssue sites of biotransformation

A
  • mostly LIVER

- also GI, kidneys, lungs (brain also has metabolic enzymes)

44
Q

CYPs

A
  • heme containing membrane proteins attached to smooth ER
  • involved in Phase I reactions
  • broad spectrum, mixed function oxidases
45
Q

CYPs involved in 50% drug metabolism

A

CYP3A4 and CYP3A5

46
Q

CYP reactions

A

involve a reductase enzyme

  • 1 O added to drug, 1 O reduced from water
  • NADPH is the energy source, no ATP needed
47
Q

Drug induction

A
  • when a drug causes an increase in liver enzyme function

- onset (3-12hours), maximal (1-5days), persistance (5-12 days)

48
Q

Pharmacogenetics

A

genetic basis for differences in responses to drugs

49
Q

Pharmacogenomics

A

application of genomic information toward development of new drugs

50
Q

Routes of drug excretion

A
  1. renal
  2. liver/intestines
  3. lungs
  4. sweat
  5. saliva
  6. breast milk
51
Q

Renal excretion processes

A

filtration
secretion
reabsorption

52
Q

What type of molecules are filtered out of the blood in the kidneys?

A
  • molecules of low molecular weight:

ions, glucose, peptides but not proteins

53
Q

What happens in the proximal tubule of the kidney?

A

Reabsorption of water

Secretion of weak electrolytes (active process - requires a transporter)

54
Q

What happens in the distal tubule of the kidney?

A

Reabsorption of nonionized weak acids/bases

55
Q

How to determine whether drug is net reabsorbed/secreted or just filtered

A

Compare clearance to GFR (normal = 120mL/min)

56
Q

Factors affecting excretion

A
  1. Drug MW
  2. Volatility
  3. Lipid solubility
  4. Concentration
  5. Volume of distribution
  6. protein binding
  7. ionization
  8. excretion mechanism
  9. rate of metabolism
  10. blood flow
  11. disease state

CMD Block 2 (38 decks)

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