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PDAT5 CV > 24 - Warfarin > Flashcards

24 - Warfarin Flashcards

1
Q

Warfarin
LAB MONITORING

A

Baseline:

  • *INR / risks of beeding**
  • *BMP** (renal fxn)
  • *CBC**

LFT @ baseline & every 12 months

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2
Q

Warfarin Drug-Disease State Interactions:

TUBE FEEDINGS

A

TUBE FEEDINGS

changes in absorption or vit K content

↓Warfarin sensitivity

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3
Q

Frequency of INR Monitoring for:

Dose held today in patient with significant supratherapeutic INR

A

Check INR within:

1 - 2 Days

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4
Q

Warfarin Dose Adjustment
Reading after >7 days of continuous dosing

INR 4.1 - 5

A

4.1 - 5

HOLD up to 2 Daily Doses
&
↓Weekly dose by 10-20%

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5
Q

Warfarin Dose Adjustment
Reading after >7 days of continuous dosing

INR 3.1 - 4

A

3.1 - 4

HOLD 1 daily dose
&
↓Weekly dose by 5-20%

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6
Q

MANAGEMENT OF HIGH INRS & BLEEDING

INR 4.5 - 10

w/o bleeding

A

Monitor INR / CBC / Bleeding

no Vit K treatment

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7
Q

Warfarin Contrainidcations

A

Pregnancy
first 3 months

Active major Bleeding

Unsupervised patients with:
Senility / Alcoholism / Psychosis / lack of cooperation

Malignant Hypertension

Lumbar Block Anesthesia

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8
Q

Frequency of INR Monitoring for:

Routine follow-up of medically for stable patients

A

Check INR within:

4 - 6 Weeks

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9
Q

Warfarin Drug-Disease State Interactions:

RENAL DISEASE

A

RENAL DISEASE

↓CYP2C9 Activity

↓Warfarin Dose Requirement

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10
Q

Warfarin Drug-Disease State Interactions

  • *Conditions that**
  • *↓warfarin sensitivity** –> require ↑Warfarin Dose
  • *↓INR**
A
  • *Chronic Alcoholism**
  • *↑**warfarin metabolism –> ↑warfarin dose
  • *Tube Feedings**
  • *↓**warfarin sensitivity, changes in absorption / vit K content
  • *HypoThyroidism**
  • *↓catabolism of clotting factors –> ↑warfarin dose**

Smoking & Chewing Tobacco
induce CYP1A2 –> ↑warfarin dose

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11
Q

Warfarin Drug-Disease State Interactions:

LIVER DISEASE

A

LIVER DISEASE

↓clotting factors & ↓warfarin clearance

↑INR

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12
Q

Frequency of INR Monitoring for:

Routine follow-up of medically unstable or unreliable patients​

A

Check INR within:

1 -2 Weeks

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13
Q

Warfarin Drug-Disease State Interactions:

HYPERThyroidism

A

HYPERThyroidism

↑catabolism of clotting factors

↑Warfarin Sensitivity

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14
Q

Warfarin Drug-Disease State Interactions:

HEART FAILURE

A

HEART FAILURE

hepatic congestion -> ↓warfarin metabolism

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15
Q

Warfarin Dose Adjustment
Reading after >7 days of continuous dosing

INR 1.5-1.9

A

1.5 - 1.9

may give extra daily dose
&
↑Weekly dose by 5-15%

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16
Q

Warfarin Drug-Disease State Interactions:

ACUTE ALCOHOL INGESTION

A

ACUTE ALCOHOL INGESTION

inhibits warfarin metabolism

↑INR

17
Q

Warfarin
Side Effects

A
  • *Fetal Hemorrhage_ & _Teratogenesis**
  • do NOT use in pregnant,* can be used postpartum okay lactation

WARFARIN INDUCED SKIN NECROSIS
Protein C & Protein S deficiency
within 1-10 days of start

Purple Toe Syndrome
develops 3-8 weeks after start

18
Q

Warfarin Dose Adjustment
Reading after >7 days of continuous dosing

INR <1.5

A

<1.5

Give extra daily dose times 1
&
↑Weekly dose by 10-20%

19
Q

When to use a
SMALLER INITIAL DOSE(<5mg)
for Warfarin

A

Increased Sensitivity to Warfarin

Older Adult / ↓Body Weight

CHF / Liver Disease / ESRD

Surgery / Diarrhea / Albumin <3

Malnourish / NPO

↑INR Meds

CYP2C9 or VKORC1 Varients

20
Q

Frequency of INR Monitoring for:

STABLE w/ current dose for 2 weeks ago

A

Check INR within:

2 - 4 Weeks

21
Q

Frequency of INR Monitoring for:

Dose Change Today

A

Check INR within:

1 - 2 Weeks

Dose change today

22
Q

MAJOR DRUG INTERACTIONS of WARFARIN:

↑ risk of bleeding = ↑ INR

A

BACTRIM** & **AMIODARONE
↓ warfarin dose by 50% & ↓ warfarin dose by 35-65%

Commonly Antibiotics = inhibit warfarin clearance = ↑ INR
Metronidazole** / **Quinolones** / **Antifungals** / **Erythromycin

STATINS** / **STEROIDS

Cimetidine / Omeprazole

Aspirin / NSAIDs

3G DIETARY SUPPLEMENTS
Garlic / Ginseng / Ginger

23
Q

Warfarin Drug-Disease State Interactions

Conditions that
↑warfarin sensitivity –> require ↓Warfarin Dose
↑INR

A
  • *Advanced Age**
  • *↓**vitamin K stores or ↓vit K clotting factors
  • *ACUTE Alcoholism**
  • inhibits warfarin metabolism* –> ↑INR
  • *Liver Disease**
  • *↓vit K clotting factors & ↓warfarin clearance –> ↑INR**
  • *Renal Disease**
  • *↓CYP2C9** activity

Heart Failure
hepatic congestion –> ↓warfarin metabolism

Cardiac Valve Replacement
↑warfarin sensitivity

HYPERthyroidism
↑catabolism of clotting factors –> ↑warfarin sensitivity

FEVER / DIARRHEA / ACUTE INFECTION / MALIGNANCY

24
Q

Warfarin Drug-Disease State Interactions:

HypoThyroidism

A

HypoThyroidism

↓catabolism of clotting factors

↑Warfarin Dose

25
Q

Warfarin Drug-Disease State Interactions:

SMOKING & TOBACCO

A

SMOKING & TOBACCO

Smoking : ↑CYP1A2

Chewing tobacco: Contains VIT K

↑Warfarin Requirements

26
Q

MANAGEMENT OF HIGH INRS & BLEEDING

INR >10

w/o bleeding

A

Give ORAL Vit K

27
Q

MANAGEMENT OF HIGH INRS & BLEEDING

Any INR

MAJOR BLEEDING

A

Rapid Reversal of AC w/ 4-factor Prothrombin

AND

Vitamin K** **5-10mg
slow IV injection

28
Q

Warfarin Drug-Disease State Interactions:

CHRONIC ALCOHOLISM

A

​CHRONIC ALCOHOLISM

↑Warfarin Metabolism

↑Warfarin DOSE

29
Q

Target INR

A

Almost Always:
2-3

Except for:
Mitral / Aortic Valve Replacement

  • *2.5-3.5
    (3) **
30
Q

Warfarin Drug-Disease State Interactions:

FEVER** or **DIARRHEA

A

FEVER** or **DIARRHEA

↑INR

Diarrhea = reduction in VITK secretion by GUT flora

Fever = Increased catabolism of clotting factors

31
Q

Warfarin

PK

A

Peak effect = 3-5 Days
depends on half life & time to deplete clotting factors
Factor 2 = longest half life

  • *S**(trong) Enantiomer = 2.7-3.8x more potent
  • *CYP2C9** > 3A4
  • 2C9 has a HIGHER impact on INR due to S being more potent*
  • *R-Enantiomer**
  • *1A2 > 3A4 > 2C19**
32
Q

Warfarin Drug-Disease State Interactions:

Acute Infection** or **Malignancy

A

Acute Infection** or **Malignancy

↑Warfarin Sensitivity

33
Q

Warfarin Drug-Disease State Interactions:

CARDIAC VALVE REPLACEMENT

A

CARDIAC VALVE REPLACEMENT

↑Warfarin Sensitivity

due to
HypoAlbuminemia & reduced oral intake

34
Q

Warfarin

MoA

A

SNOT - C+S

Interferes with conversion of:
Vitamin K Epoxide

Inhibits activation of:
Seven Nine 1O Two

Inhibits:

  • *Protein C** + S
  • natural inhibitors of coagulation cascade*
35
Q

MAJOR DRUG INTERACTIONS of WARFARIN:

↓ anticoagulant effectiveness​ = ↓ INR

A
  • *RIFAMPIN**
  • may require a HIGER dose of warfarin*

Barbiturates

Cholestyramine

Carbamazepine

ST. JOHNS WORT = CYP450 inducer

↑ warfarin metabolism –> ↓ anticoagulant effectiveness​ = ↓ INR

PDAT5 CV (30 decks)

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