Anticoagulation: an age-adjusted warfarin loading regimen was better than the Fennerty regimen

Clinical bottom line (level 2b)

  1. Patients loaded with an age-adjusted warfarin regimen compared with Fennerty's regimen were less likely to have a dose withheld (NNT = 3 at 8 days) and an INR of 4.0 or more (NNT = 4 at 8 days) .
  2. Patients on the age-adjusted regimen were more likely to have a stable INR after a week (NNT = 3 at 8 days).
Roberts et al: Australian and New Zealand Journal of Medicine 1999; 29 : 731-736
Expires June 2004

The study

Unblinded ?concealed quasi-randomised trial without intention-to-treat
Setting: 2 teaching hospitals, Australia

63 patients (aged mean 74, 70% male) starting warfarin

Excluded if
  • vitamin K supplementation within previous 2 weeks.
  • nasogastric or enteral feeds
  • commencing amiodarone at same time as warfarin
  • advanced malignancy
  • undergoing mitral or aortic valve replacement
  • prolonged diarrhoea (3 days or more)

    Note:
  • Patients had doses reduced by 33% if they had severe congestive heart failure (ejection fraction < 30% and/or biventricular failure), severe COPD (oxygen or steroid dependent or dyspnoea at rest) or concurrent amiodarone use.


Control Group: (n = 30, 28 analysed): Fennerty warfarin loading protocol
Experimental Group: (n = 37, 35 analysed): age-adjusted warfarin loading protocol
Patients received warfarin at 1600 daily, and had INR levels checked between 0800 and 0900 the next morning. The target INR was 2.0 to 3.0.
97% followed for 8 days
Outcome notes:

  • stable INR : 2.0 to 3.0 for 2 consecutive days

The evidence

Outcome Time to outcome CER EER RRR
(95% CI)		 ARR
(95% CI)		 NNT
(95% CI)
warfarin dose withheld 8 days 11
(39.3%)		 2
(5.71%)		 85%
(40% to 96%)		 33.6%
(13.9% to 52.3%)		 3
(2 to 7)
INR 4.0 or more 7 days 9
(32.1%)		 2
(5.71%)		 82%
(24% to 96%)		 26.4%
(7.50% to 45.4%)		 4
(2 to 13)
stable INR 8 days 9
(32.1%)		 0
(0.0%)		 100%
(% to %)		 32.1%
(14.8% to 49.4%)		 3
(2 to 7)

Comments

  1. Eight medical units were randomly assigned to either the Fennerty or age-adjusted regemin (50 patients). Surgical units used the age-adjusted regemin for 6 weeks followed by the Fennerty regimen (13 patients).

Citation

  1. Roberts GW, Druskeit T, Jorgensen LE, et al: comparison of an age adjusted warfarin dosing loading protocol with empirical dosing and Fennerty's protocol. Australian and New Zealand Journal of Medicine 1999; 29 : 731-736
Search Terms: ?
Contributor: Chris Ball, June 2001
Reviewer: Clare Wotton

Clinical Question.
Patient commencing anticoagulation with warfarin
Intervention or Exposure age-adjusting loading protocol
Comparison Fennerty loading protocol
Outcome stable INR, dose withheld, supratherapeutic INR