03. Pharmacokinetics Flashcards

1
Q

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

  • thiopental cannot be administered through a GI tract route.

T/F?

A

False. Can be given PR, absorbed well.

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2
Q

Neostigmine is better absorbed from the GI tract than physostigmine. T/F

A

False.

Neostigmine is quaternary and charged,
physostigmine is a tertiary amine

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3
Q

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

diazepam
fentanyl
phenytoin
ibuprofen
lidocaine
A

fentanyl and lidocaine.

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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4
Q

T/F:

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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5
Q

T/F: 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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6
Q

Forumla to calculate Vd in one-compartment model?

A

volume of distribution is given by clearance divided by rate constant for elimination

(Vd = Cl/k)

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7
Q

Which of these enzymes show the most significant pharmacogenetic variation?

CYP2E1
CYP2D6
CYP3A5
CYP2C9
CYP1A2
A

CYP 2D6 - metabolism of codeine conversion to morphine.

CYP 2C9 - metabolism of S-warfarin

26 + 29

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8
Q

Mivacurium elimination?

A

mivacurium is broken down by butyrylcholinesterase,

cisatracurium and atracurium are degraded by the Hofmann process

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9
Q

True or false:

For a ONE compartment model, 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

rate of elimination proportional to plasma concentration.

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10
Q

True or false:

in a ONE compartment model, the behaviour of the drug can be predicted as long as the clearance is known.

A

False.

To know the behaviour of a drug, you need to know:

  1. volume of distribution
  2. time constant (or rate constant for elimination)
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11
Q

In a 3 compartment model, what are the most important factors to determining the variability of the CSHT?

A
  • duration of the infusion.

- the ratio of elimination to redistribution.

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12
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.

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13
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).

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14
Q

In patients with hepatic failure and ascites:

The bioavailability of drugs with a moderate heptic extraction ratio is increased or decreased?

A

The bioavailability increases - metabolic capacity will be reduced as may hepatic flow.

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15
Q

Which of the following will increase hepatic extraction of propofol:

Dobutamine
Ciprofloxacin
Carbamezapine
Noradrenaline
Chronic alcohol intake
A

Dobutamine - increases hepatic blood flow.

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16
Q

Which of the following drugs readily cross the placenta

Select true or false for each of the following statements.

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

S-bupivacaine, fentanyl and isoflurane, diazepam