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E-lfh FRCA Primary: Pharmacology - Pharmacokinetics > Primary FRCA Course Paper 02 Pharmacokinetics > Flashcards

Primary FRCA Course Paper 02 Pharmacokinetics Flashcards

1
Q

The rate of drug absorption from the stomach is (true or false):

lower for fentanyl than diclofenac

A

True. fentanyl is a weak base with a pKa of 8.4 so is almost entirely ionized in the stomach; diclofenac is a weak acid with pKa of 4 and will be largely unionized in the stomach

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2
Q

The rate of drug absorption from the stomach is (true or false):

greater for weak acids than weak bases for drugs with a pKa of 6

A

True

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3
Q

The rate of drug absorption from the stomach is (true or false):

increased in the presence of metoclopramide

A

False. metoclopramide increases gastric emptying, so reduces drug concentration in the stomach, which reduces rate of absorption from the stomach. Overall. Absorption may be increased, especially for basic drugs - but this is not what the question asks

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4
Q

The rate of drug absorption from the stomach is (true or false):

always increased by omeprazole

A

False. The absorption of weak acids in the stomach will be slowed by PPIs

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5
Q

The rate of drug absorption from the stomach is (true or false):

less important than absorption from the small intest

A

True. In general the greater absorptive area of the small bowel accounts for a greater proportion of drug absorption

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6
Q

When considering absorption of drugs from the gastrointestinal (GI) tract

fentanyl is better absorbed from the small intestine than the stomach

A

True. The pH of the small bowel is higher than the stomach, so weak bases are better absorbed

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7
Q

When considering absorption of drugs from the gastrointestinal (GI) tract

thiopental cannot be administered through a GI tract route

A

False. Thiopental can be administered rectally; it is absorbed fairly well

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8
Q

When considering absorption of drugs from the gastrointestinal (GI) tract

atracurium cannot be given orally

A

True. Atracurium is a bis-quaternary molecule that is permanently charge and not absorbed from the GI tract

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9
Q

When considering absorption of drugs from the gastrointestinal (GI) tract

Neostigmine is better absorbed than physostigmine

A

False. Neostigmine is quaternary and charged, physostigmine is a tertiary amine

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10
Q

When considering absorption of drugs from the gastrointestinal (GI) tract

Ketoconazole absorption is increased in patients taking omeprazole

A

False. Ketoconazole is a weak base but is so lipophilic that oral preparations cannot dissolve in hydrophilic gastric juice unless they can be ionized. By increasing gastric pH PPIs reduce the degree of ionization and so the solubility of ketoconazole

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11
Q

Which of the following drugs bind more to alpha-1 acid glycoprotein than to albumin

A. diazepam
B. fentanyl
C. phenytoin
D. ibuprofen
E. lidocaine

A

B & E

In general acidic/neutral drugs bind to albumin and basic drugs or those with a quaternary nitrogen, to alpha-1 acid glycoprotein. Lidocaine and fentanyl are basic drugs, ibuprofen is acidic and diazepam/phenytoin are neutral - they are not water soluble

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12
Q

Which of the following are true of plasma protein binding of therapeutic drugs

displacement of protein-bound drug by a second drug will necessarily cause toxic effects

A

False. Toxic effects seen only if the therapeutic ratio is small and hepatic extractio ratio is very low

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13
Q

Which of the following are true of plasma protein binding of therapeutic drugs

drugs with a low hepatic extraction ratio and high degree of protein binding are most affected by changes in protein binding

A

True

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14
Q

Which of the following are true of plasma protein binding of therapeutic drugs

drugs that show flow-dependent hepatic extraction are unaffected by changes in protein binding

A

True

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15
Q

Which of the following are true of plasma protein binding of therapeutic drugs

the interaction between amiodarone and warfarin is entirely due to competition for plasma protein binding sites

A

False. This interaction is mainly due to a metabolic interaction: amiodarone inhibits CYP2C9

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16
Q

Which of the following are true of plasma protein binding of therapeutic drugs

the renal filtration rate of a drug is increased when plasma protein binding is decreased

A

True

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17
Q

Regarding the distribution of drugs through the body

the volume of distribution at steady state for a drug is dependent only on its lipid solubility

A

False. although lipid soluble drugs can have very large volumes of distribution, if a drug is rapidly metabolized then it will have a much smaller volume of distribution that might be expected from its lipid characteristics : eg remifentanil

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18
Q

Regarding the distribution of drugs through the body

in a one-compartment model, volume of distribution is directly proportional to drug clearance

A

True. volume of distribution is given by clearance divided by rate constant for elimination (Vd = Cl/k)

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19
Q

Regarding the distribution of drugs through the body

drugs with greater than 95% protein binding have a relatively small volume of distribuition

A

False. propofol has a very large volume of distribution but also is greater than 98% bound - so this is clearly untrue

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20
Q

Regarding the distribution of drugs through the body

volume of distribution at steady state is approximately equal to total body water for most drugs

A

False. volume of distribution varies greatly between drugs: large for propofol, small for atracurium

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21
Q

Regarding the distribution of drugs through the body

non-depolarizing muscle relaxants have a smaller volume of distribution than induction agents

A

True. ndmrs are charged molecules and do not cross lipid membranes so have relatively small volumes of distribution

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22
Q

Which of the following describe the distribution of propofol

it has a volume of distribution of approximately 1.4 L/kg

A

False. Its Vd at steady state has variously been estimated to be as high as 20-60 L/kg, but lower values are found for short infusions. However, in general it has a volume of distribution of at least 4 L/kg

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23
Q

Which of the following describe the distribution of propofol

it is an acidic drug so binds to albumin in plasma

A

True

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24
Q

Which of the following describe the distribution of propofol

the volume of distribution is very large as it is essentially unionized at plasma pH

A

True

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25
Q

Which of the following describe the distribution of propofol

the initial volume of distribution in adults is age-dependent

A

False. None of the kinetic models identify age as an independent variable for predicting initial Vd

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26
Q

Which of the following describe the distribution of propofol

the volume of distribution is high because propofol is highly protein-bound

A

False. Vd is high because it is extremely lipid soluble and essentially unionized

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27
Q

The following are metabolites of atracurium

cisatracurium

A

False. this is just one of the 10 isomers of atracurium, not a metabolite

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28
Q

The following are metabolites of atracurium

desmethylatracurium

A

False

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29
Q

The following are metabolites of atracurium

laudanosine

A

True. a product of the minor (Hofmann) metabolic pathway

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30
Q

The following are metabolites of atracurium

3,17-dihydroxy atracurium

A

False. the aminosteroids are broken down by deacetylation at the 3 and 17 positions

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31
Q

The following are metabolites of atracurium

a monoquaternary alcohol derivative

A

True. a product of the major (ester hydrolysis) pathway

32
Q

Which of the following enzymes demonstrate important pharmacogenetic variation

A. CYP2E1
B. CYP2D6
C. CYP3A5
D. CYP2C9
E. CYP1A2

A

B & D

CYP2D6 - This is responsible for codeine conversion to morphine. 10% of Caucasians are poor metabolizers

CYP2C9 - This is responsible for the metabolism of S-warfarin

33
Q

Which of the following drugs have an oral bioavailability of more than 75%

A. aspirin
B. paracetamol
C. oramorph
D. diclofenac
E. ibuprofen

A

A. False. about 65%
B. True. about 90%
C. False. about 25%
D. False. about 50%
E. True. more than 80%

34
Q

The following routes of elimination are the major route for the named drug

lungs: sevoflurane

A

True. >95% excreted unchanged

35
Q

The following routes of elimination are the major route for the named drug

renal: benzylpenicillin

A

True. rapid excretion by tubular secretion

36
Q

The following routes of elimination are the major route for the named drug

red cell esterases: esmolol

A

True

37
Q

The following routes of elimination are the major route for the named drug

tissue esterases: remifentanil

A

True. plasma esterase activity also contributes, but tissue (especially muscle) esterases are most important

38
Q

The following routes of elimination are the major route for the named drug

non-enzymic plasma degradation: mivacurium

A

False. mivacurium is broken down by butyrylcholinesterase, cisatracurium and atracurium are degraded by the Hofmann process

39
Q

In a one-compartment model for the kinetics of a drug

if volume of distribution stays the same, clearance increases if the time constant decreases

A

True

40
Q

In a one-compartment model for the kinetics of a drug

the volume of distribution at steady state can be calculated using a single bolus dose of drug

A

True. There is just one volume to consider

41
Q

In a one-compartment model for the kinetics of a drug

the context sensitive half time is proportional to the duration of an infusion

A

False. the CSHT is always constant and equal to the half-life

42
Q

In a one-compartment model for the kinetics of a drug

after giving an intravenous bolus dose, the rate of elimination at a particular time is dependent only on the clearance

A

False. it is proportional to plasma concentration - an exponential relationship - whereas clearance is constant

43
Q

In a one-compartment model for the kinetics of a drug

the behaviour of the drug can be predicted as long as the clearance is known

A

False. you need two parameters to describe the behaviour of the drug: volume of distribution and time constant (or rate constant for elimination). Clearance simple gives you the ratio of these two values To describe behaviour completely, you need to know both parameters individually, not just the ratio

44
Q

If a drug given by continuous intravenous infusion behaves according to a three-compartment model

the volume of distribution at steady state is the most important determinant of the variability of the context sensitive half time

A

False. the duration of the infusion and the ratio of elimination to redistribution rather than Vdss are most important: if elimination is very rapid and redistribution from compartments 2 and 3 is slow, then CSHT will not vary as much as if elimination were rapid and redistribution also rapid

45
Q

If a drug given by continuous intravenous infusion behaves according to a three-compartment model

the second compartment has three rate constants associated with it

A

False. elimination occurs only from the first (central) compartment, so there are just two: k12 and k21

46
Q

If a drug given by continuous intravenous infusion behaves according to a three-compartment model

if the plasma level has reached steady state, then clearance out of the body can be calculated from the infusion rate and concentration

A

True

47
Q

If a drug given by continuous intravenous infusion behaves according to a three-compartment model

drug can be removed from the system from any of the three compartments

A

False. in the 3-C model, we adopt a mammilary, not a catenary model; elimination is allowed only from the central compartment

48
Q

If a drug given by continuous intravenous infusion behaves according to a three-compartment model

the effect compartment equilibrates with the central compartment

A

True

49
Q

When considering elimination of drug from the body

the rate of elimination is equal to the clearance

A

False. rate of elimination = clearance multiplied by drug concentration

50
Q

When considering elimination of drug from the body

if glomerular filtration rate doubles, then the amount of free drug excreted through the urine also doubles

A

False. urinary elimination depends also on tubular secretion

51
Q

When considering elimination of drug from the body

CYP450 enzymes are found only in hepatocytes

A

False. CYP450 enzymes are expressed in many tissues

52
Q

When considering elimination of drug from the body

hepatic enzymes involved in xenobiotic metabolism are exclusively associated with the smooth endoplasmic reticulum

A

False. there are CYP enzymes in the SER, but metabolic enzymes are also found in the cytoplasm (alcohol dehydrogenase) and associated with mitochondria (MAO)

53
Q

When considering elimination of drug from the body

more than 99% of the drug will have been eliminated after three half-lives

A

False. after 5 half-lives or 3 time constants

54
Q

For a simple one-compartment model

the half-life is longer than the time constant

A

False. the time constant is always longer than the half-life

55
Q

For a simple one-compartment model

the rate constant for elimination is found from the slope of the graph that plots log(concentration) against time

A

True

56
Q

For a simple one-compartment model

clearance is the ratio of the volume of distribution to the time constant

A

True. Clearance = Vd/tau = Vd x k, where tau is the time constant and k the rate constant for elimination

57
Q

For a simple one-compartment model

the volume of distribution multiplied by the rate constant for elimination divided by plasma concentration is equal to the clearance

A

False. this is the rate of elimination.

Rate of elimination (k) = Concentration (mg/ml) x clearance (ml/min)

Clearance = Vd x k

58
Q

For a simple one-compartment model

the shape of the curve that describes the rise of drug concentration with time on starting a constant rate infusion is a negative exponential

A

True. wash-in curves are negative exponentials because the rate at which concentration changes decreases with time [ Css(1 - exp(-kt))]

59
Q

In patients with hepatic failure and acsites

the volume of distribution for hydrophilic drugs is reduced

A

False. In general Vd increases with ascites

60
Q

In patients with hepatic failure and acsites

the metabolism of all drugs is reduced

A

False. many drugs are affected, but not all

61
Q

In patients with hepatic failure and acsites

the bioavailability of drugs with a moderate heptic extraction ratio is increased

A

True. metabolic capacity will be reduced as may hepatic flow, so it is likely that bioavailability will be increased

62
Q

In patients with hepatic failure and acsites

the terminal elimination half-life for remifentanil is unaffected

A

True

63
Q

In patients with hepatic failure and acsites

the dose of non-depolarizing muscle relaxants required for intubation is increased

A

True. Maintenance doses may need reducing, but the increased initial Vd means a larger initial dose may be needed

64
Q

Which of the following will increase hepatic extraction of propofol. Explain why for each.

A. dobutamine
B. ciprofloxacin
C. carbamezepine
D. noradrenaline
E. chronic alcohol intake

A

A only, as it increases hepatic blood flow

B. False. ciprofloxacin inhibits CYP1A2, not those enzymes primarily responsible for propofol metabolism (CYP2B6 and CYP2C9). Though they may interact to produce QT prolongation
C. False. CYP inducer, but hepatic ER already approaches 1
D. False. cardiac output not necessarily increased, so hepatic flow not increased
E. False. propofol is not metabolized by CYP2E1

65
Q

A mammilary three-compartment model used to model effect-site targeting of drug concentration

elimination occurs from the effect site

A

False. The effect site is considered to have a negligible volume and so elimination from this compartment is not a part of the 3-C model

66
Q

A mammilary three-compartment model used to model effect-site targeting of drug concentration

the volume of the effect site is not included in the volume of distribution at steady state

A

True

67
Q

A mammilary three-compartment model used to model effect-site targeting of drug concentration

there are two inter-compartmental clearances included in the model

A

True. In a 3-C model there are three clearances to consider: two inter-compartment clearances and one out-of-system (body) clearance

68
Q

A mammilary three-compartment model used to model effect-site targeting of drug concentration

the t1/2keo describes the rate of equilibration between plasma and effect compartments

A

True. This parameter describes the lag between plasma concentration changes and effect compartment changes

69
Q

A mammilary three-compartment model used to model effect-site targeting of drug concentration

clearance from the system can be found from steady-state infusion rate and plasma concentration

A

True. Input = output principle applies for steady state infusions - the difficulty lies with knowing when steady-state has been reached

70
Q

When measuring bioavailability

drug behaviour must be fitted to a known model in order to calculate bioavailability

A

False. A non-model-based method is used: AUC(oral)/AUC(IV) if looking at oral bioavailability

71
Q

When measuring bioavailability

bioavailability refers only to oral compared with intravenous administration

A

False. Any route can be assessed for bioavailability compared with the standard route of administration (usually IV)

72
Q

When measuring bioavailability

oral bioavailability can be found by dividing clearance of the drug when given orally by the clearance found when given IV

A

False. Clearance should be the same for a drug whether it is given orally or intravenously: bioavailability is the ratio of the area under the concentration-time curve (AUC) for the oral route divided by the AUC for the IV route

73
Q

When measuring bioavailability

the same dose of drug must be given orally and intravenously to find oral bioavailability

A

True

74
Q

When measuring bioavailability

interindividual variability must be expected

A

True. Bioavailability of a given drug for a particular patient will differ depending on many factors including health problems and concurrent medication

75
Q

Which of the listed drugs have a volume of distribution at steady state greater than total body water

A. cisatracurium
B. neostigmine
C. atropine
D. noradrenaline
E. sevoflurane

A

C & E.

Permanently charged molecules do not distribute across lipid membranes so the muscle relaxants and neostigmine have small volumes of distribution. Atropine and sevoflurane are very lipid soluble and will distribute into lipid areas. Noradrenaline is ionized at body pH and modeling is consistent with rapid metabolism so calculated Vd is small

76
Q

Which of the following drugs readily cross the placenta

A. S-bupivacaine
B. diazepam
C. fentanyl
D. succinylcholine
E. isoflurane

A

All except D.

Lipid soluble drugs cross the placenta more rapidly than drugs that are ionized at plasma pH; permanently charged drugs do not cross the placenta so muscle relaxants will not affect the fetus

E-lfh FRCA Primary: Pharmacology - Pharmacokinetics (1 decks)

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