Anticoagulation

Question 1

Unfractionated Heparin (UFH) - Monitoring

Answer 1

• Check aPTT within 6hrs
  
  • Reference Range: 25-39s
  • Therapeutic Goal Range: 1.5-2.5 x control aPTT
    
    • 45-75 seconds (for control of 30s)
• Check Plateletes qod x 14 days or until UFH is stopped, whichever occurs first.
  
  • Monitoring for HIT (platelets < 100,000 or < 50% of baseline)

Question 2

Low Molecular Weight Heparin (LMWH) - Monitoring

Answer 2

• Routine monitoring is not necessary

Question 3

Warfarin - Monitoring

Answer 3

• INR Reference Range: around 1
• INR Goal Range: typically 2.0-3.0
  
  • 2.5-3.5 for certain prosthetic heart valves
• If INR can be obtained daily, check every day for five days.
• If INR cannot be obtained daily check at:
  
  • day 3/4
  • day 5-7
  • day 8-10
  • day 11-14

Question 4

Compare and contrast safety and efficacy of warfarin, dabigatran, and rivaroxaban.

Answer 4

Dabigatran and Rivaroxaban:

• are at least as effective as warfarin for stroke propylaxis
• have a faster onset than warfarin
• have fewer drug interactions than warfarin
• cause less intracranial bleeding than warfarin
• have a higher risk for GI bleeding than warfarin
• do not have an antidote
• require more srict adherence than warfarin
• are more risky to use for patients with renal insuffiency
• should not be used for patients with mechanical heart valves

Question 5

Compare the monthly cost of warfarin, dabigatran, and rivaroxaban.

Answer 5

Warfain: $80 per month including INR assessment

Dabigatran: $250 per month

Rivaroxaban: $230 per month

Question 6

What does aPTT stand for and what is the reference range?

Answer 6

activated partial thromboplastin time

25-39 seconds

Question 7

historical therapeutic range equation

Answer 7

1.5 - 2.5 X Control aPTT

Question 8

what does INR stand for?

Answer 8

International Normalized Ratio

Question 9

How do you calculate INR?

Answer 9

INR= PT patient/PT control

PT is the prothrombin time result.

goal range varies depending on indication

Question 10

Discuss the significance of CYP2C9 variants with regard to warfarin dosing and potential adverse effects.

Answer 10

CYP2C9 genotype is associated with

1) warfarin maintenance dose
2) time to stable warfarin dose
3) rate of above range INRs
4) bleeding events

Question 11

Define Pharmacogentics.

Answer 11

Study of variability in hereditary factors as it relates to drug response in different populations.

Question 12

Discuss the common clinically significant drug interactions that occur with warfarin and their management.

Answer 12

Sulfamethoxazole increases the anticoagulation effect by inhibiting cytochrome p450 which inhibits metabolism of warfarin. Aspririn and NSAIDS increase bleeding risk with their antiplatelet effects which makes it harder for platelets to stick together.

Question 13

For patients on Oral Anticoagulants (Dabigatran/Pradaxa, Rivaroxaban/Xarelto, and Apixaban/Eliquis) what kind of monitoring and follow-up is required?

Answer 13

No monitoring is required for anticoagulation, however, with Eliquis monitoring of renal function and subsequent adjustment of dose should be done prn.