Warfarin therapy

Before starting treatment
- Counsel patient. Check that they are able to understand system:
  - Patient aware of potential problems with drug interactions, particularly aspirin.
  - Patient has a phone.
  - Patient can attend casualty for INR tests early morning or arrrange district nurse.
  - Patients must be aware of the importance of the tests.
  - Patient should take their warfarin dose at 6pm.
- Check baseline FBC, PT, APPT
Starting treatment
- Prescribe warfarin 1mg x100 (brown), 3mg x100 (blue), 5mg x100 (pink) on repeat prescription.
- Add current problem Warfarin monitoring which will contain INR results
- Initiate treatment with
  - Loading dose Saturday
  - Loading dose Sunday
  - INR Monday
- Suggested loading doses 10mg/10mg or 10mg/5mg for small patients or those on interacting medication.
- Give written instructions to the patient about starting doses and times (use System 6000 warfarin WP template).
- Give patient completed referral form and yellow book to go with first INR test and instruct patient that the laboratory will phone them on the Monday evening to advise them what dose to take.
Continuing treatment
- Use Wansbeck INR dosing service with yellow book for all patients.

INR	Indication	INR	Indication
2.0-3.0	DVT prophyllaxis (general)	2.0-3.0	Atrial fibrillation
2.0-3.0	DVT prophyllaxis (hip fractures)	2.0-3.0	Valvular heart disease
2.0-3.0	MI prevention of venous thromboembolism	2.0-4.0	Recurrent DVT/PE
2.0-3.0	DVT treatment	2.0-4.5	Arterial disease/MI
2.0-3.0	PE treatment	3.0-4.5	Mechanical prosthetic valves
2.0-3.0	TIA's	3.0-4.5	Recurrent systemic embolism
2.0-3.0	Tissue heart valves

No analgesic is entirely without analgesic risk.
All analgesic-warfarin interactions potentiate warfarin and raise the INR.
Patients in pain may not be eating: fasting also raises the INR.
Interactions can be accommodated if the interacting drug is taken regularly: avoid prn analgesic dosage.
Paracetamol and paracetamol/codeine combinations are least likely to upset warfarin control.
Co-proxamol is contraindicated in patients taking warfarin.
NSAID's should not be used when only simple pain relief is required.
When NSAID is clearly indicated (eg acute gout)
- reduce warfarin dose by 25-30%
- check INR in 2-4 days with drug details on request form.
All controlled drug analgesics have major interactions with warfarin. Check INR 2-4 days after starting dihydrocodeine, pethidine, buprenorphine and all morphine analogues - and 2-4 days after any change in dose.
Anticonvulsants (for neurogenic pain) may alter INR. Check INR 2-4 days after starting or each dose change.