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Apex > Pharmacokinetics > Flashcards

Pharmacokinetics Flashcards

1
Q

What is the equation for volume of distribution?

A

Vd = amount of drug/desired plasma concentration

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2
Q

What is the total distribution of body water in a 70 kg patient?

A

42L

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3
Q

How many liters of fluid are located in the intracellular region?

A

28

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4
Q

How many liters of fluid are located in the extracellular fluid?

A

14L

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5
Q

Of the extracellular fluid, how many liters are located in the interstitial fluid?

A

10L

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6
Q

Of the extracellular fluid, how many are located in the plasma volume?

A

4L

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7
Q

A drug with a Vd that > TBW (> 0.6 L/kg or > 42L) is assumed to be what?

A

Lipophilic

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8
Q

A drug with a Vd < TBW (<0.6 L/kg or < 42L) is assumed to be what?

A

Hydrophilic

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9
Q

What are some key traits about a drug that is lipophilic with a high Vd (>42L)?

A

It distributes into the total body water as well as into the fat

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10
Q

What is the equation for the loading dose of a drug?

A

Loading dose = Vd x desired plasma concentration/ 1

(this is assuming it is an IV drug with 100% bioavailability)

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11
Q

What are the most important clearing organs?

A

Liver
Kidney
Organ independent (Hoffman)

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12
Q

What is clearance directly proportional to?

A

Blood flow to cleaning organ
Extraction ratio
Drug dose

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13
Q

What is clearance inversely proportional to?

A

Half-life
Drug concentration in the central compartment

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14
Q

What does a steady state mean?

A

The amount of drug entering body = amount of drug eliminated from body

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15
Q

As a general rule, when is steady state achieved?

A

5 half-lives

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16
Q

When looking at the plasma concentration curve, what does the alpha phase represent?

A

Distribution

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17
Q

What looking at the plasma concentration curve, what does the beta phase represent?

A

Elimination

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18
Q

What is the concept of context sensitive half-time?

A

It’s the time required for the plasma concentration to decline by 50% after the infusion is stopped

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19
Q

What is the Ionization of a drug is dependent on what two factors?

A

The pH of the solution
The pKa of the drug

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20
Q

What exactly is pKa?

A

It’s a constant property of a molecule

A drug’s pKa equals the pH where 50% of the drug is ionized and the other 50% is non-ionized.

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21
Q

What is the Henderson-Hasselbach equation?

A

pH= pKa + log (base) / conjugate acid

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22
Q

What are some properties of an ionized molecule? Traits

A

Solubility: water (hydrophilic)
Pharmacological effect: not active
Hepatic Biotransformation: less likely
Renal Elimination: More likely
Diffuses across lipid bilayer: BBB, GI tract, or placenta —> no

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23
Q

What are some properties of a non-ionized molecule?

A

Solubility: lipophilic
Pharmacologic effect: yes, active
Hepatic bio transformation: more likely
Renal elimination: no
Diffuse across a lipid bilayer: BBB, GI tract, Placenta —> yes

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24
Q

Which local anesthetic is most likely to undergo fetal ion trapping? Which is the least likely?

A

Most likely: Lidocaine
Least likely: chloroprocaine (d/t it’s high pKa and rapid metabolism)

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25
Q

What are some key facts about albumin in terms of plasma protein binding?

A

Most plentiful plasma protein
Determines oncotic pressure
1/2 life: 3 weeks
Negative charge
Primarily binds to ACIDIC drugs

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26
Q

In what conditions is albumin decreased?

A

Liver disease
Malnutrition
Renal dx
Old age
PREGNANCY

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27
Q

What are some key facts about a1- Acid Glycoprotein?

A

Binds with basic drugs

28
Q

When is a1 acid Glycoprotein increased? What decreases it?

A

Increased: surgical stress
MI
chronic pain
RA
Advanced age

When is it decreased: pregnancy neonates

29
Q

What is the equation to determine changes in plasma protein binding?

A

Percent change= New value - Old Value / old value x 100%

30
Q

What is zero order kinetics? What are some examples?

A

A constant AMOUNT of the drug is metabolized per unit time

Ex: asa, phenytoin, alcohol, warfarin, heparin, theophylline

31
Q

What is first order kinetics?

A

A constant FRACTION of the drug is metabolized per unit time

Most of our drugs are this.

32
Q

What is the key organ for metabolism? What is another important site?

A

Key: Liver
Plasma

33
Q

What is the primary role of metabolism?

A

Change a lipid-soluble, active compound to a water soluble, inactive compound

34
Q

What is it called when the body converts an inactive molecule into a pharmacologically active molecule?

A

Prodrug!

35
Q

What are the 3 phases of metabolism?

A

Phase 1: Modification
Phase 2: Conjugation
Phase 3: Elimination

36
Q

What are the three types of phase 1 reactions?

A

Oxidation —> removes electrons
Reduction —> adds elections
Hydrolysis —> adds water to split

37
Q

What does it mean to be perfusion dependent?m in terms of hepatic elimination?

A

This is for drugs with a high hepatic extraction ratio (> 0.7) ~ clearance depends on liver blood flow.

^ liver blood flow = ^ clearance
Decrease in blood flow = decrease in clearance

38
Q

What does it mean to be capacity dependent on terms of hepatic elimination?

A

Drugs that have a low hepatic extraction ratio (< 0.3). Clearance is dependent on the ability of the liver to extract the drug from blood. Changes in hepatic enzymes and/or protein binding affect clearance

^ enzyme induction = ^ clearance
Enzyme inhibition = decrease clearance

39
Q

What are examples of high hepatic extraction rations and/or perfusion-dependent drugs?

A

Most anesthetics/opioids

Propofol
Fent
Ketamine
Morphine
Lidocaine
BBS
CCBs

40
Q

What are examples of low hepatic extraction ratio? An/or drugs that are capacity-dependent?

A

Roc
Diazepam
Lorazepam
Methadone
Thiopental
Theophylline
Phenytoin

41
Q

What are two specific enzymes of the P450 system that pertain to anesthesia? They are important

A

CYP 3A4 (most of our anesthetics)

CYP 2D6 (some opioids) morphine, oxycodone, hydrocodone

42
Q

Name some examples of enzyme inducers? What do these do?

A

Increase clearance —> decrease drug level —> may need increased dose

Tobacco
Barbiturates
Ethanol
Phenytoin
Rifampin
Carbamazepine
St. John’s Wort

43
Q

What are examples of an enzyme inhibitor? What does it do?

A

Inhibits enzyme activity —> decreases clearance —> increased plasma levels—> smaller dose may be required

Grapefruit juice
Cimetidine
Omeprazole
Isonaizid
SSRIs
Erythromycin
Ketoconazole
Cipro

44
Q

Acidic urine favors what? Think elimination

A

Reabsorption of acidic drugs
Excretion of basic drugs
AAA (Acids are better Absorbed in an Acid medium)

45
Q

Basic urine favors what? Think elimination

A

Reabsorption of basic drugs
Excretion of acidic drugs
BBB: Basic drugs are Better absorbed in a Basic medium)

46
Q

What drugs are metabolized by pseudocholinesterases?

A

Sux
Mivacurium
Ester local anesthetics (cocaine, tetracaine)

47
Q

What drugs are eliminates by non-specific esterases?

A

Esmolol
Remi
Atracurium (+ Hoffman)
Etomidate
Clevidipine

48
Q

What describes the relationship b/t effect-site concentration and the clinic effect?

A

Pharmacodynamics

“What the drug does to the body”

49
Q

What describes the relationship b/t the drug dose and plasma concentration?

A

Pharmacokinetics

“What the body does to the drug”

(Think absorption, distribution, metabolism, elimination)

50
Q

What is one the x axis when looking at the dose-response curve?

A

Potency

51
Q

What is on the y axis is on dose-response curve?

A

Efficacy

52
Q

What is the ED50? What is the ED90?

A

ED 50 —> dose required to achieve a given affect in 50% of the population

ED 90 —> dose required to achieve a given affect in 90% of the population

53
Q

When considering the dose-response curve, what does a left-shift mean?

A

Increased potency —> lower dose required

54
Q

When considering the dose-response curve, what does a right shift mean?

A

Lower potency —> higher dose is required.

55
Q

What is efficacy?

A

Measure of the intrinsic ability of a drug to elicit a given clinical effect

56
Q

What does the slope on the dose response curve indicate?!

A

Slope tells you how many receptors must be occupied to elicit a clinical effect.

Steep slope: most receptors must be fully occupied

57
Q

What is an example of addition?

A

Effect of two drugs given at the same time are added to each other (1+1=2)

Morphine + hydromorphone

58
Q

What is an example of synergism?

A

The effect of two drugs given at the same time is greater than their individual effects.

(1+1=3)

Propofol and midazolam

59
Q

What is potentiation?

A

Effect of one drug is enhanced by a drug that has no effect of its own

1+0=3

PCN and probenecid

60
Q

What is antagonism?

A

Simultaneous administration of one drug negates the effect of a second drug

1+1=0

Fent and naloxone

61
Q

How do you calculate therapeutic index?

A

Therapeutic index= LD50 / ED50

62
Q

What is the TD50?

A

The dose that will produce toxicity in 50% of the population

63
Q

What is the LD50?

A

The dose that produces death in 50% of the population.

64
Q

What is a racemic mixture?

A

It’s a mixture that contains two enantiomers in equal amounts.

65
Q

What are some examples of enantiomers?

A

Ketamine
Thiopental
Isoflurane
Desflurane
Mepivacaine

66
Q

What are two exceptions that are prepared as single enantiomers instead of as racemic mixture?

A

Ropivacaine
Levobupivacaine

67
Q

What are ways you can acidify the urine?
What are ways you can alkaline the urine?

A

Acidify: ammonium chloride or cranberry

Alkalize: acetazolamide

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