Warfarin Prescribing

1
Warfarin Prescribing

• Presented by Sally Marotti
• Prepared by Jennifer MacDonald
• July 2008

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).
• 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
• initials of nurse that administers the dose and
  the checking nurse
• Pharmacists will also annotate the chart when
  possible

6
Warfarin Chart Audit

• 21 patients on warfarin at JHH who had 342 days
  of warfarin charted on 65 medication charts
• 16 doses were not given (5). 10 of these did not
  have the dose charted by the medical officer and
  nursing staff therefore did not administer
• 31 (9) doses did not have the dose signed by the
  medical officer
• 27 INR results were not documented on the charts
• Indication not recorded in 55, target INR not
  recorded in 15

7
Warfarin Chart Audit

• Time to therapeutic INR for some patients was
  excessive (12 days)
• The use of the eighth day of the chart for
  warfarin creates issues for other medications
  with pm dosing as nursing staff are unable to
  sign when administered
• Nomenclature and signing for doses to be withheld
  was poor (w/h, X, 0mg etc)

8
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!!

9
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

10
Age-adjusted warfarin initiation protocol
11
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 sign
• Do not use the eighth day column

12
CAPAC (Community Acute/Post Acute Care Service)

• Referral for anticoagulation in the community

Non-clinical exclusion criteria

• Less than 16 years of age (parent/guardian
  consent required if lt18)
• Resides outside CAPAC catchment area
• Not able to transfer and mobilise
  independently
• Patient unable to obtain adequate rest and
  nutritionNo access to telephone
• Home environment not safe for health care
  worker home visits
• Patient behaviours not safe for health care
  worker home visits
• Does not agree to CAPAC providing treatment
  at home

Clinical Exclusion Criteria - General
13
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

14
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

15
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

16
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

17
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

18
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

19
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

20
Case Study Two
30/10
1.1
1.6
7.5
0.5
2-3
po
DVT
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

21
Case Study Two
30/10
1.1
1.8
2.2
7.5
0.5
4
2-3
po
DVT
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

22
Case Study Two
30/10
1.1
1.8
1.6
4.1
7.5
0.5
4
w/h
2-3
1
po
DVT
MC
MC
MC
MC
MC
RN CN
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