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Pharmacokinetics > Block 3 > Flashcards

Block 3 Flashcards

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1
Q

What drugs do CYP2D6 metabolize?

A

Antiarrhythmics

Antidepressants

Antipsychotics

BB (not atenolol)

Codeine + Tramadol

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2
Q

What are the PM alleles associated w/ CYP2D6?

A

CYP2D6 * 3,4,5,6

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3
Q

CYP2D6 PM + Codeine, what happens?

A

PM cant form active metabolite (morphine) and cannot experience pain relief

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4
Q

CYP2D6 UM + Codeine, what happens?

A

Increased rate of morphine metabolites and causes respiratory depression; fatal to newborns

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5
Q

CYP2D6 PM + Antipsychotics, what happens?

A

Increased extrapyramidal side effects

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6
Q

CYP2D6 PM + Tamoxifen, what happens?

A

PM cant form metabolites and their treatment outcomes are worse

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7
Q

PM of CYP2D6 are found in what population?

A

Whites and Asians

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8
Q

What drugs do CYP2C9 metabolize

A

Phenytoin

Warfarin

NSAIDs

ARBs

Glipizide and Glyburide

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9
Q

What are the PM alleles associated w/ CYP2C9?

A

CYP2C9 * 2,3,5

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10
Q

Reduced function of CYP2C9 is found in what population?

A
  • 2 and *3 is found in whites, much less prevalent in blacks and asians
  • 5 is found only in blacks
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11
Q

(R or S) - Warfarin is associated with 60-70% of its anticoagulant effect

A

S-warfarin; that is the one metabolized by CYP2C9 and differences w/ genotype impact the dose

R-warfarin is metabolized by CYP3A4 and 1A2

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12
Q

What is the key factor in explaining the variability in warfarin dose?

A

Vitamin K oxidoreductase complex 1 gene (VKORC1)

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13
Q

What variation would put someone in the NM, IM, and PM section for CYP2C9?

A

NM = 1/1

IM = 1/2 or 1/3

PM = 2/2 or 2/3

Side effects are more prevalent in phenytoin with variant alleles

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14
Q

What are the alleles associated with CYP2C19?

A

CYP2C19 *2,3,17

-only *2 and *3 are associated w/ PM

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15
Q

What populations groups are affected by CYP2C19?

A

*2 and *3 occur in whites and asians

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16
Q

CYP2C19 PM + PPI, what happens?

A

Higher concentration, therefore you expect increased % of AE

PPI have a wide safety margin and therefore work better to treat H.pylori infections

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17
Q

What antiplatelet Rx requires CYP2C19?

A

Clopidogrel (pro-drug)

CYP2C19 activates it to its active moiety, therefore PM dont get the effect of the drug

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18
Q

What is the most abundant CYP enzyme in the liver?

A

CYP3A4

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19
Q

CYP3A422
CYP3A41B
Por*28

Which one is associated w/ reduced activity?

A

CYP3A4*22

Other 2 are increased activity

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20
Q

Which variant of CYP3A5 contain partial loss expression compared to CYP3A5*1?

A

*3

Others are 6,8,9,10

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21
Q

Which variant of CYP3A5 require the highest and lowest dose?

A
  • 1/*1 = highest (lowest plasma concentration)

* 3/*3 = lowest dose (highest plasma concentration)

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22
Q

Which population group is affected by CYP3A5?

A

Blacks and whites

Blacks - Most are 1/1 or 1/3

Whites - Most are 3/3

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23
Q

What drug requires CYP3A5?

A

Tacrolimus

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24
Q

Cigarette smoking induces what CYP enzyme?

A

CYP1A2*1F; enhances clearance affected by this substrate

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25
What drugs do CYP1A2 metabolize?
Caffeine Theophylline Clozapine + Olanzapine Activates procarcinogens
26
P-glycoprotein is encoded by what gene?
ABCB1 gene
27
Which haplotype of ABCB1 is normal and which ones are abnormal?
Normal - CC (most renal/biliary excretion) Abnormal - CT (kind of impaired, therefore more drugs enter blood vessel) -TT (Totally impaired, therefore most of the drug enters blood vessel, most reduced renal/biliary excretion)
28
Warfarin class?
Oral anticoagulant; Vitamin K antagonist
29
Warfarin MOA?
Competitively inhibits C1 subunit of VKORC1 and interferes with clotting factors II, VII, IX, X. Also affects protein C + S
30
Warfarin indications?
Tx and prevent VTE Tx and prevent TE associated w/ A.Fib and cardiac valve replacement Reduce risk of death, MI, amd TE after MI
31
PK info on Warfarin?
Racemic mix of R and S enatiomer but the major one is S Highly protein bound (99%)
32
PD info on Warfarin?
Takes 24 - 72 hrs for onset Takes 2-5 days for duration Peak effect in 3-4 days
33
What population groups are highly affected by warfarin?
Geriatric + Asians Geriatric - have higher INR response (more sensitive) Asians - require lower initiation and maintenance dose
34
CI of warfarin?
Pregnant (unless you have a mechanical heart valve, Eclampsia, preeclampsia, and threatened abortion Unsupervised pt w/ high potential for noncompliance
35
AE of warfarin?
Major bleed + Skin necrosis
36
What RX/food decreases warfarin effect?
Rifampin Barbiturates Carbamazepine Phenytoin St. John's Wort
37
What RX/food increases warfarin effect?
ABx Antifungals Thyroid Rx Steroids Lipid drugs Grapefruit Amiodarone
38
What are the variants of VKORC1?
GG GA (intermediate warfarin sensitivity) AA (highly sensitive to warfarin)
39
What are the tablet colors and doses on warfarin?
1, 2, 2.5, 3, 4, 5, 6, 7.5, 10 Pink, Lavender, Green, Brown, Blue, Peach, Teal, Yellow, White **Please Let Greg Brown Bring Peaches To Your Wedding**
40
How do you calculate INR?
Patient's Prothrombin time / Mean prothrombin normal range Low = increased clot risk High = increased bleed risk Baseline INR ~1
41
INR goal (warfarin) of 2.5 to 3.5 is indicated for who?
Mechanical mitral valve replacement and dual aortic with mitral valve replacement If you see mechanical aortic valve, bioprosthetic, or rheumatic, its goal is 2-3
42
INR goal (warfarin) of 2-3 is indicated for who?
Stroke Tx and prevention VTE Antiphospholipid syndrome
43
Frequency of INR monitoring
Every 2-3 days during initiation and until INR is achieved Every 1-2 wks when INR is achieve TWICE or when there is dose adjustments Every 4 wks if INR has been stable for 2 consecutive readings Every 8-12 wks if INR has been stable for ≥6 months
44
What are the anticoagulation reversal Rx?
Vit. K + Kcentra
45
How is Vit. K administered?
PO or IV, NEVER IM
46
Anticoagulation reversal and INR <4.5 w/ no bleed, what should you do?
Vit. K NOT recommended Hold and/or reduce warfarin
47
Anticoagulation reversal and INR <10 w/ no bleed, what should you do?
Vit. K NOT recommended Hold AND reduce warfarin
48
Anticoagulation reversal and INR >10, what should you do?
Give low dose ORAL vit. K (2.5-5mg)
49
Anticoagulation reversal with MINOR bleed at any INR, what should you do?
HOLD warfarin May give low dose ORAL vit. K (2.5-5mg)
50
Anticoagulation reversal with MAJOR bleed at any INR, what should you do?
Give Kcentra instead of plasma May or may not give Vit. K 5-10mg IV slowly
51
Phenytoin class?
Anticonvulsant for tonic-clonic or partial seizures
52
What is the maintenance dose equation for phenytoin?
[Vmax * Css] / [S(F) * (Km+Css)]
53
What could increase Vmax and affect phenytoin MD dose calculations?
Enzyme induction (phenobarbital or carbamazepine administration)
54
What could decrease Vmax and affect phenytoin MD dose calculations?
Hepatic cirrhosis
55
What could increase Km and affect phenytoin MD dose calculations?
Competitive inhibition (cimetidine or chloramphenicol administration
56
What could decrease Km and affect phenytoin MD dose calculations?
Decreased plasma protein binding by having low serum albumin
57
How do you calculate Vmax and Km for someone on phenytoin w/ normal renal and hepatic function
Vmax = 7mg/kg/day Km = 4micrograms/mL
58
What are the ways to check steady-state of phenytoin?
Two levels are drawn a week apart within 10% value Wait 2-4 wks after dose change then obtain level
59
What routes should be avoided in phenytoin?
IM; painful and precipitates in muscle which gives it prolonged absorption
60
What is the max rate of IV phenytoin?
Do NOT exceed 50mg/min, it will cause hypotension
61
What is the equivalent rate of fosphenytoin and phenytoin?
100mg PE of fosphenytoin = 100mg phenytoin
62
Phenytoin vs Fosphenytoin, which one is water-soluble?
Fosphenytoin
63
Phenytoin vs Fosphenytoin, which one has less hypotension issues?
Fosphenytoin
64
What is the max rate of IV fosphenytoin?
150mg PE/min
65
What is the salt factor in phenytoin?
Assume 0.92 unless it is a suspension or chewable tablet, then its 1. 1 because of phenytoin acid form
66
What is the therapeutic unbound phenytoin levels? Total levels?
1-2 microgram/mL - unbound only 10-20 microgram/mL - unbound and bound** **standard monitoring method
67
What are some causes of protein binding changes in pt w/ phenytoin that can cause their unbound fraction to jump to 30-40%?
Hypoalbuminemia Liver or Kidney issue (endogenous) Certain drugs like warfarin, valproic acid, NSAIDs (exogenous)
68
How do you calculate loading dose of phenytoin?
LD = [Css*Vd] / (S)(F) Vd = 0.65/kg or 1.3/kg if obese

Pharmacokinetics (3 decks)

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