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Clinical Pharmacist, Pharmacy Department, Repatriation General Hospital, Daw Park, Australia
Research Pharmacist, Royal Danish School of Pharmacy, Copenhagen, Denmark
Research Pharmacist, Royal Danish School of Pharmacy
Director of Southpath, Flinders Medical Center, Bedford Park, Australia
Pharmacology Registrar, Clinical Pharmacology, Flinders Medical Center
Deputy Director, Pharmacy Department, Repatriation General Hospital
Senior Specialist Clinical Pharmacist, Division of Pharmacy, Flinders Medical Center
Reprints: Gregory W Roberts BPharm, Pharmacy Department, Repatriation General Hospital, Daws Road, Daw Park SA 5041, Australia, FAX 61-8-8374 0225, E-mail greg.roberts{at}rgh.sa.gov.au
OBJECTIVE: To examine the time taken to reach a stable international normalized ratio (INR), as well as the incidence of overanticoagulation of an age-adjusted warfarin initiation protocol.
METHODS: Inpatients and outpatients commencing warfarin therapy at 2 teaching hospitals were dosed according to the age-adjusted protocol. Data were collected prospectively.
MAIN OUTCOME MEASURES: Time to reach a stable INR of
2–3 and the number of patients experiencing an INR 
4 during the
first week of warfarin therapy.
RESULTS: Seventy-three patients were assessed; at the
completion of the 4-day titration protocol, 63% had achieved a stable INR.
After an additional 2 days of empiric dosage adjustment by the attending
physician, 86% of the subjects demonstrated a stable INR. Five patients (7%)
experienced an INR 4. These patients had a nonsignificant trend toward a
lower plasma albumin level compared with other patients (p = 0.057, Student's
t-test). The INR-driven dose adjustments on days 3 and 4 of this
protocol coped with other variables that have been shown to affect maintenance
warfarin dosing. These included weight, gender, pharmacologic factors
affecting clearance, and the presence of certain predesignated risk
factors.
CONCLUSIONS: The age-adjusted dosing protocol rapidly achieved a stable INR with minimal overanticoagulation. Patients with low serum albumin levels (<3.0 g/dL) may be sensitive to the effects of warfarin during the loading phase.
Key Words: elderly, loading dose, warfarin
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