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Clinically Based Concepts > module 3: clinical scenario metabolism > Flashcards

module 3: clinical scenario metabolism Flashcards

1
Q

why are drugs coated with enteric coatings?

A

to prevent them from breaking down while they are in an acidic environment, low surface area, and poor absorption from the stomach

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2
Q

what cells line the small intestines?

A

enterocytes

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3
Q

what is the purpose of villi and microvilli?

A

dramatically increase the surface area of the small intestine and aid in the absorption of food

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4
Q

what is the first barrier for a drug that enters your system?

A

enterocytes

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5
Q

what is the most prominent drug metabolizing enzyme in the enterocytes?

A

CYP3A4

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6
Q

list the three fractions a single dose of medication follows once swallowed?

A
  1. one fraction failed to make it into the enterocytes
  2. one fraction metabolized by CYP3A4 in the enterocytes
  3. remaining fraction made it through the enterocytes unscathed
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7
Q

what is the main function of the liver?

A

metabolize molecules for their removal from the body via kidneys

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8
Q

true or false: drugs can be directly removed in bile

A

true

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9
Q

true or false: for most drugs, liver metabolism typically activates them and makes them more soluble for their removal

A

false: inactivates

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10
Q

what comprises the hepatic portal network?

A

intestinal capillary network and portal vein

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11
Q

true or false: small amounts of the drug that weren’t metabolized in the enterocytes can still be metabolized as they circulate because enzymes like CYP3A4 are everywhere

A

true

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12
Q

define bioavailability

A

amount of a drug that’s available to the biological tissues of the body

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13
Q

what is the bioavailability of a drug administered IV and why?

A

100% because it enters the systemic circulation

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14
Q

what is the bioavailability of a drug administered orally: For example, if 60% of a drug makes it through the enterocytes without being metabolized, but 50% of that is metabolized by CYP3A4 in the liver.

A

30%

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15
Q

what are first pass effects?

A

very little reaches the systemic circulation

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16
Q

what is the most common way to bypass first pass effects?

A

administering drugs IV

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17
Q

how does administering drugs IM minimize first pass effects?

A

enters the circulation via lymphatic system

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18
Q

how does administering drugs sublingual minimize first pass effects?

A

enter the systemic system circulation through sublingual vessels

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19
Q

how can drugs be inhaled and enter the systemic circulation?

A

via pulmonary capillaries that are closely associated with alveoli in the lungs

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20
Q

what is the pathway of drugs once it reaches the systemic circulation?

A

vena cava -> heart -> aorta -> liver via hepatic artery

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21
Q

what is the portal triad?

A

how drugs enter the liver through the portal vein and hepatic artery in a bundle with the bile duct region

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22
Q

what is the functional unit of the liver?

A

liver acinus

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23
Q

where does metabolism of hydrophilic drugs occur?

A

cytosol

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24
Q

where do hydrophobic drugs metabolize?

A

smooth ER

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25
Q

what are phase I drug metabolizing enzymes?

A

enzymes that oxidize and/or reduce drugs

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26
Q

what are phase II drug metabolizing enzymes?

A

enzymes that add other groups to drugs

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27
Q

true or false: phase I and II designations reflect the order that drugs are metabolized

A

false

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28
Q

what are the enzymes of phase I?

A

cytochrome P450 identified with designation CYP

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29
Q

how is CYP denoted?

A

family
subfamily
isoform

30
Q

describe the isoform CYP2C9

A

phase I
- narrower range of substrates including the anticoagulant warfarin and ibuprofen

31
Q

what is the overall purpose of CYP?

A

oxidizing enzymes that involve the removal of electrons in the process of transferring oxygen containing species like hydroxyl groups to drugs

32
Q

phase II uses conjugation, what is that?

A

enzymes that most often add a molecule to a drug to make it more soluble in water

33
Q

why do we want to make drugs more water soluble?

A

so it can be excreted in the urine

34
Q

when is a drug considered to be metabolized?

A

after is has become altered by one or both sets of reactions

35
Q

what does 450 mean in cytochrome P450

A

spectrophotometric peak occurs at 450 nm under a particular set of conditions

36
Q

why are the CYP enzymes called oxidase?

A

they transfer oxygen to the drugs they metabolize

37
Q

how do CYP enzymes transfer oxygen?

A

electrons have to be removed from the drug and from the oxygen-containing functional groups to form a covalent bond between the drug and the oxygen species.

38
Q

why are some CYP enzymes considered reductases?

A

both reduction and oxidation occur (redox reactions)

39
Q

why is cytochrome P450 considered heme containing enzymes?

A

the heme groups in the enzymes bind oxygen

40
Q

the heme group in the CYP enzymes is covalently linked to the amino acid _________ and contains an _______ atom that plays a critical role in these reactions.

A

cysteine
Fe

41
Q

what is cysteine important for in CYP enzymes?

A

transfer of the oxygen-containing functional groups to the drugs

42
Q

The Fe atom oscillates between being in what three oxidation states depending on the what is happening in the redox reactions?

A

Fe2+, Fe3+ , and Fe4+

43
Q

the reduced heme group in cytochrome P450 enzymes strongly bind to what?

A

carbon monoxide

44
Q

how did cytochrome P450 get its name?

A

they contain a heme group that binds carbon monoxide and maximally absorbs light at the specific wavelength of 450 nm.

45
Q

what happens when a drug binds near the heme of the CYP enzyme in the presence of oxygen?

A

the drug covalently binds one of the oxygen atoms in O2, the other O2 combines with two H+ to form water

46
Q

how does NADP+ become NADPH

A

when it becomes reduced it can hold onto H+ to form NADPH

47
Q

where and how does H+ come together to form water?

A

they can donate H+ to O2

48
Q

how many NAPHs are needed to complete the reaction of water formation?

A

2 because water has 2 H+

49
Q

when can NADPH donate its H+?

A

becomes oxidized and loses an electron

50
Q

what enzyme is needed to oxidize NADPH?

A

oxidase, CYP450 enzymes

51
Q

what is the result of the phase I reaction?

A
  • drug with a polar group and creation of water molecule
  • 2 NADPH2 oxidized to NADP+ and ready to be reduced again whenever electrons become available
52
Q

it is extremely important that NADP+ and NADPH are available to gain or donate an __________

A

electron

53
Q

what kind of enzymes are involved in the phase II drugs?

A

transferases

54
Q

what are the molecules that can be transferred?

A

acetyl
sulfur
glucuronosyl
methyl groups

55
Q

which of the transferred groups is hydrophobic?

A

methyl group

56
Q

what is a conjugation reaction?

A

when a molecule gets transferred to a drug

57
Q

what is the most prominent reaction handled by conjugative phase II enzymes?

A

glucuronidation

58
Q

how is the compound of bilirubin formed?

A

in the liver when heme groups are extracted from red blood cells being removed at the end of their normal lifespan

59
Q

what groups are transferred to bilirubin via a transferase enzyme?

A

glucuronosyl

60
Q

where does the glucuronosyl group come from?

A

UDP

61
Q

In the presence of the UGT enzyme, where is bilirubin conjugated and secreted into?

A

the bile and eventually released into the lumen of the small intestine.

62
Q

While in the small intestine, the glucuronidated bilirubin can be metabolized further by bacterial enzymes to form either ________ or _________.

A

stercobilin
urobilinogen

63
Q

Some of the urobilinogen is reabsorbed in the ______________, excreted by the ______, and forms urobilin when exposed to the air.

A

small intestines
kidneys

64
Q

what is stercobilin?

A

breakdown product of bilirubin that leaves through the gastrointestinal tract and is the compound that causes feces to be brown.

  • a biomarker used to document fecal contamination in rivers
65
Q

what gives urine its yellow color?

A

urobilinogen

66
Q

What happens if the UGT enzyme isn’t present?

A

bilirubin can’t be properly conjugated and metabolized

67
Q

what are some symptoms of Gilbert’s syndrome?

A
  • yellow tinge of skin and whites of eyes
  • tired and weak
  • abdominal pain
68
Q

explain the bloodwork results of someone with Gilbert’s syndrome

A

they are unable to transfer glucuronate moiety to bilirubin (unconjugated bilirubin) so the bloodwork would reveal a high concentration of bilirubin (hyperbilirubinemia) lacking the glucuronosyl group

69
Q

what does isoniazid become when it is metabolized?

A

acetylisoniazid

70
Q

how does acetyl get added to isoniazid?

A

acetyl CoA

71
Q

what is the main function of acetyl CoA?

A
  • deliver an acetyl group to oxaloacetate to form citric acid in the citric acid cycle
  • vital for cellular metabolism
  • helps in many phase II reactions involving transfer of acetyl group

Clinically Based Concepts (10 decks)

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