Warfarin Prescribing

1
Warfarin Prescribing

• Prepared by Jennifer MacDonald
• Deputy Director of Pharmacy
• 27 October 2006

2
Warfarin Sodium

• 2 brands Coumadin (1 mg, 2 mg and 5 mg) and
  Marevan (1 mg, 3 mg and 5 mg) DONT
  SUBSTITUTE as not bioequivalent
• High risk medication (narrow therapeutic range)
• Too much bleed
• Too little clot
• Patients have variable responses to treatment
• Goal for initiation
• Rapidly attain a stable therapeutic INR without
  over-anticoagulation

3
Monitoring INR (International Normalised Ratio)

• Target INR 3.0 4.5 older mechanical heart
  valves
• 2.5 3.5 newer mechanical heart valves
• 2.0 3.0 other indications
• Determine INR on day 1 then daily or on
  alternate days until stable
• Dosage changes not reflected fully in INR for 2-3
  days

4
National Inpatient Medication Chart
2-3
PE

• The warfarin ordering section is printed in red
  as an extra alert to indicate that it is an
  anticoagulant (and a high-risk medicine).
• Standard dose time of 1600 hours (4pm) - allows
  the medical team caring for the patient to order
  the next dose based on INR results, rather than
  leaving it for after-hours staff to do PLUS INR
  tested 16 hours post (8am). As many patients take
  their Warfarin as an evening dose, there is a
  need for consistency between home and hospital to
  avoid confusion, additionally rural facilities in
  our area do not have INR results by 4pm,
  therefore we advise that where possible 4pm is a
  charting time and not an administration time.
• The indication and target INR should be included
  when warfarin is initially ordered.

5
National Inpatient Medication Chart
30/10
1.1
10
2-3
po
PE
MC
Imprest
RN CN
Dr Marevan
2310

• For each day of therapy, the following
  information should be documented
• INR result
• warfarin dose
• doctors initials (even if the dose is to be
  withheld)
• initials of nurse that administers the dose and
  the checking nurse
• Pharmacists will also annotate the chart when
  possible

6
Age Adjusted Warfarin Initiation Protocol

• Developed trialled by Haematology
  Pharmacology JHH QUMC approved
• Rapid achievement of a stable INR with minimal
  over-anticoagulation
• Coped with other variables shown to affect
  maintenance warfarin dosing, such as weight,
  gender, pharmacologic factors affecting
  clearance, and risk factors.
• NOTE does not replace thinking!!

7
Age Adjusted Warfarin Initiation Protocol

• Day 1 INR reflects pre-warfarin baseline. If
  gt1.4, reasons for coagulopathy should be
  assessed.
• Warfarin doses on Days 2-4 are based on INR
  measured 16hrs after the previous days dose
• Patients with low albumin may be particularly
  sensitive to the anti-coagulation effects of
  warfarin
• Consider decreasing dose by around one third if
  the patient has one or more of the following
• Severe congestive cardiac failure (ejection
  fraction lt30 and/or biventricular failure)
• Severe airways disease (oxygen/steroid dependent
  or dyspnoea at rest)
• Concurrent amiodarone

8
Age-adjusted warfarin initiation protocol
9
Safe warfarin prescribing

• Prescribe and sign EACH days doses
• Look up and write INR results on charts
• Include INR target indication when prescribing
• Use the Age Adjusted Warfarin protocol
• Endorse doses to be withheld as w/h and initial
  to indicate whose decision this was
• Do not use the eighth day column as the remainder
  of the chart is not in use on the 8th evening and
  Warfarin dose may therefore be missed

10
Case Study One

• 32 year old (65kg) patient Lisa Thrombus presents
  to hospital with severe leg pain and is diagnosed
  with a DVT
• She is commenced on warfarin po and enoxaparin
  100mg sc daily
• Her day 1 baseline INR is 1.1
• Fill out the chart provided to reflect this
  information

11
Case Study One
30/10
1.1
10
2-3
po
DVT
MC
RN CN
Dr Marevan
2310

• On day two you measure her INR at 8am (16 hours
  post dose) and the result returns as 1.8
• Fill out the chart provided to reflect this
  information, and provide a dose based on the age
  adjusted warfarin protocol

12
Case Study One
30/10
1.1
1.8
10
0.5
2-3
po
DVT
MC
MC
RN CN
Dr Marevan
2310

• On day three you measure her INR at 8am and the
  results return as 1.6
• Fill out the chart provided to reflect this
  information, and provide a dose based on the age
  adjusted warfarin protocol

13
Case Study One
30/10
1.1
1.8
1.6
10
0.5
10
2-3
po
DVT
MC
MC
MC
RN CN
RN CN
Dr Marevan
2310

• On day four you measure her INR at 8am and the
  results return as 2.5
• Fill out the chart provided to reflect this
  information, and provide a dose based on the age
  adjusted warfarin protocol

14
Case Study One
30/10
1.1
1.8
1.6
2.5
10
0.5
10
5
2-3
po
DVT
MC
MC
MC
MC
RN CN
RN CN
RN CN
Dr Marevan
2310

• A 4.5mg 5.5mg dose range is appropriate

15
Case Study Two

• 78 year old (85kg) patient Maurice Embolus
  presents to hospital with SOB and chest pain. He
  is diagnosed with a pulmonary embolus.
• He is commenced on warfarin and heparin 5000
  units IV bolus followed by IV infusion 1000-2000
  units/hr adjusted according to APTT until
  therapeutic
• His pre-warfarin baseline INR is 1.2
• Fill out the chart provided to reflect this
  information

16
Case Study Two
30/10
1.2
7.5
2-3
po
PE
MC
RN CN
Dr Marevan
2310

• On day two you measure his INR at 8am (16 hours
  post dose) and the result returns as 1.6
• Fill out the chart provided to reflect this
  information, and provide a dose based on the age
  adjusted warfarin protocol

17
Case Study Two
30/10
1.1
1.6
7.5
0.5
2-3
po
PE
MC
MC
RN CN
Dr Marevan
2310

• On day three you measure his INR at 8am and the
  results return as 2.2
• Fill out the chart provided to reflect this
  information, and provide a dose based on the age
  adjusted warfarin protocol

18
Case Study Two
30/10
1.1
1.8
2.2
7.5
0.5
3.5
2-3
po
PE
MC
MC
MC
RN CN
RN CN
Dr Marevan
2310

• On day four you measure his INR at 8am and the
  results return as 4.1
• Fill out the chart provided to reflect this
  information, and provide a dose based on the age
  adjusted warfarin protocol

19
Case Study Two
30/10
1.1
1.8
1.6
4.1
po
7.5
0.5
3.5
w/h
2-3
1
PE
MC
MC
MC
MC
MC
RN CN
RN CN
RN CN
Dr Marevan
2310

• Next days dose should be withheld then commence
  again in dose range 0.5mg 1.5mg